diff --git a/HISTORY.rst b/HISTORY.rst
index 780d980..5dc0811 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -3,4 +3,4 @@ History
 =======
 
 
-* First release on PyPI.
+* 0.2.1 version usada en produccion.
diff --git a/facho/facho.py b/facho/facho.py
index 0970c2c..b64a6d4 100644
--- a/facho/facho.py
+++ b/facho/facho.py
@@ -389,94 +389,12 @@ class FachoXML:
 
     def get_element(self, xpath, multiple=False):
         xpath = self.fragment_prefix + self._path_xpath_for(xpath)
-        return self.builder.xpath(self.root, xpath, multiple=multiple)
-
-    def get_element_text(self, xpath, format_=str, multiple=False):
-        xpath = self.fragment_prefix + self._path_xpath_for(xpath)
-        # MACHETE(bit4bit) al usar ./ queda ../
-        xpath = re.sub(r'^\.\.+', '.', xpath)
-
-        elem = self.builder.xpath(self.root, xpath, multiple=multiple)
-        if multiple:
-            vals = []
-            for e in elem:
-                text = self.builder.get_text(e)
-                if text is not None:
-                    vals.append(format_(text))
-            return vals
-        else:
-            text = self.builder.get_text(elem)
-            if text is None:
-                return None
-            return format_(text)
-
-    def get_element_text_or_attribute(
-            self, xpath, default=None, multiple=False, raise_on_fail=False):
-        parts = xpath.split('/')
-        is_attribute = parts[-1].startswith('@')
-        if is_attribute:
-            attribute_name = parts.pop(-1).lstrip('@')
-            element_path = "/".join(parts)
-            try:
-                val = self.get_element_attribute(
-                    element_path, attribute_name, multiple=multiple)
-                if val is None:
-                    return default
-                return val
-            except KeyError as e:
-                if raise_on_fail:
-                    raise e
-                return default
-            except ValueError as e:
-                if raise_on_fail:
-                    raise e
-                return default
-        else:
-            try:
-                val = self.get_element_text(xpath, multiple=multiple)
-                if val is None:
-                    return default
-                return val
-            except ValueError as e:
-                if raise_on_fail:
-                    raise e
-                return default
-
-    def get_elements_text_or_attributes(self, xpaths, raise_on_fail=True):
-        """
-        returna el contenido o attributos de un conjunto de XPATHS
-        si algun XPATH es una tupla se retorna el primer elemento del mismo.
-        """
-        vals = []
-        for xpath in xpaths:
-            if isinstance(xpath, tuple):
-                val = xpath[0]
-            else:
-                val = self.get_element_text_or_attribute(
-                    xpath, raise_on_fail=raise_on_fail)
-            vals.append(val)
-        return vals
-
-    def exist_element(self, xpath):
-        elem = self.get_element(xpath)
-
-        # no se encontro elemento
+        elem = self.builder.xpath(self.root, xpath)
         if elem is None:
-            return False
+            raise AttributeError('xpath %s invalid' % (xpath))
 
-        # el placeholder no ha sido populado
-        if elem.get('facho_placeholder') == 'True':
-            return False
-
-        # el valor opcional no ha sido populado
-        if elem.get('facho_optional') == 'True':
-            return False
-
-        return True
-
-    def _remove_facho_attributes(self, elem):
-        self.builder.remove_attributes(
-            elem, ['facho_optional', 'facho_placeholder'])
+        text = self.builder.get_text(elem)
+        return str(text)
 
     def tostring(self, **kw):
         return self.builder.tostring(self.root, **kw)
diff --git a/facho/fe/form/__init__.py b/facho/fe/form/__init__.py
index 026eef8..7659e16 100644
--- a/facho/fe/form/__init__.py
+++ b/facho/fe/form/__init__.py
@@ -60,9 +60,10 @@ class AmountCollection(Collection):
 
 class Amount:
     def __init__(
-            self, amount: typing.Union[int, float, str, "Amount"],
-            currency: Currency = Currency('COP')):
-
+            self, amount: int or float or str,
+            currency: Currency = Currency('COP'),
+            precision=DECIMAL_PRECISION):
+        self.precision = precision
         # DIAN 1.7.-2020: 1.2.3.1
         if isinstance(amount, Amount):
             if amount < Amount(0.0):
@@ -76,9 +77,10 @@ class Amount:
 
             self.amount = Decimal(
                 amount, decimal.Context(
-                    prec=DECIMAL_PRECISION,
+                    prec=self.precision,
                     # DIAN 1.7.-2020: 1.2.1.1
-                    rounding=decimal.ROUND_HALF_EVEN))
+                    rounding=decimal.ROUND_HALF_EVEN)
+            )
             self.currency = currency
 
     def fromNumber(self, val):
@@ -96,20 +98,24 @@ class Amount:
     def __lt__(self, other):
         if not self.is_same_currency(other):
             raise AmountCurrencyError()
-        return round(self.amount, DECIMAL_PRECISION) < round(other, 2)
+        return round(self.amount, self.precision) < round(other, 2)
 
     def __eq__(self, other):
         if not self.is_same_currency(other):
             raise AmountCurrencyError()
-        return round(self.amount, DECIMAL_PRECISION) == round(
-            other.amount, DECIMAL_PRECISION)
+        return round(self.amount, self.precision) == round(
+            other.amount, self.precision)
 
     def _cast(self, val):
         if type(val) in [int, float]:
             return self.fromNumber(val)
         if isinstance(val, Amount):
             return val
-        raise TypeError("cant cast to amount")
+
+        if isinstance(val, Decimal):
+            return self.fromNumber(float(val))
+
+        raise TypeError("cant cast %s to amount" % (type(val)))
 
     def __add__(self, rother):
         other = self._cast(rother)
diff --git a/facho/fe/model/__init__.py b/facho/fe/model/__init__.py
new file mode 100644
index 0000000..6b10421
--- /dev/null
+++ b/facho/fe/model/__init__.py
@@ -0,0 +1,367 @@
+import facho.model as model
+import facho.model.fields as fields
+import facho.fe.form as form
+from facho import fe
+from .common import *
+from . import dian
+
+from datetime import date, datetime
+from collections import defaultdict
+from copy import copy
+import hashlib
+
+
+
+class PhysicalLocation(model.Model):
+    __name__ = 'PhysicalLocation'
+
+    address = fields.Many2One(Address, namespace='cac')
+    
+class PartyTaxScheme(model.Model):
+    __name__ = 'PartyTaxScheme'
+
+    registration_name = fields.Many2One(Name, name='RegistrationName', namespace='cbc')
+    company_id = fields.Many2One(ID, name='CompanyID', namespace='cbc')
+    tax_level_code = fields.Many2One(ID, name='TaxLevelCode', namespace='cbc', default='ZZ')
+
+
+class Party(model.Model):
+    __name__ = 'Party'
+
+    id = fields.Virtual(setter='_on_set_id')
+    name = fields.Many2One(PartyName, namespace='cac')
+
+    tax_scheme = fields.Many2One(PartyTaxScheme, namespace='cac')
+    location = fields.Many2One(PhysicalLocation, namespace='cac')
+    contact = fields.Many2One(Contact, namespace='cac')
+    
+    def _on_set_id(self, name, value):
+        self.tax_scheme.company_id = value
+        return value
+
+class AccountingCustomerParty(model.Model):
+    __name__ = 'AccountingCustomerParty'
+
+    party = fields.Many2One(Party, namespace='cac')
+
+class AccountingSupplierParty(model.Model):
+    __name__ = 'AccountingSupplierParty'
+
+    party = fields.Many2One(Party, namespace='cac')
+
+class Quantity(model.Model):
+    __name__  = 'Quantity'
+
+    code = fields.Attribute('unitCode', default='NAR')
+
+    def __setup__(self):
+        self.value = 0
+
+    def __default_set__(self, value):
+        self.value = value
+        return value
+
+    def __default_get__(self, name, value):
+        return self.value
+
+class Amount(model.Model):
+    __name__ = 'Amount'
+
+    currency = fields.Attribute('currencyID', default='COP')
+    value = fields.Amount(name='amount', default=0.00, precision=2)
+
+    def __default_set__(self, value):
+        self.value = value
+        return value
+
+    def __default_get__(self, name, value):
+        return self.value
+
+    def __str__(self):
+        return str(self.value)
+
+class Price(model.Model):
+    __name__ = 'Price'
+
+    amount = fields.Many2One(Amount, name='PriceAmount', namespace='cbc')
+    
+    def __default_set__(self, value):
+        self.amount = value
+        return value
+
+    def __default_get__(self, name, value):
+        return self.amount
+
+class Percent(model.Model):
+    __name__ = 'Percent'
+
+class TaxScheme(model.Model):
+    __name__ = 'TaxScheme'
+
+    id = fields.Many2One(ID, namespace='cbc')
+    name= fields.Many2One(Name, namespace='cbc')
+
+class TaxCategory(model.Model):
+    __name__ = 'TaxCategory'
+
+    percent = fields.Many2One(Percent, namespace='cbc')
+    tax_scheme = fields.Many2One(TaxScheme, namespace='cac')
+    
+class TaxSubTotal(model.Model):
+    __name__ = 'TaxSubTotal'
+
+    taxable_amount = fields.Many2One(Amount, name='TaxableAmount', namespace='cbc', default=0.00)
+    tax_amount = fields.Many2One(Amount, name='TaxAmount', namespace='cbc', default=0.00)
+    tax_percent = fields.Many2One(Percent, namespace='cbc')
+    tax_category = fields.Many2One(TaxCategory, namespace='cac')
+
+    percent = fields.Virtual(setter='set_category', getter='get_category')
+    scheme = fields.Virtual(setter='set_category', getter='get_category')
+
+    def set_category(self, name, value):
+        if name == 'percent':
+            self.tax_category.percent = value
+            # TODO(bit4bit) debe variar en conjunto?
+            self.tax_percent = value
+        elif name == 'scheme':
+            self.tax_category.tax_scheme.id = value
+
+        return value
+
+    def get_category(self, name, value):
+        if name == 'percent':
+            return value
+        elif name == 'scheme':
+            return self.tax_category.tax_scheme
+
+class TaxTotal(model.Model):
+    __name__ = 'TaxTotal'
+
+    tax_amount = fields.Many2One(Amount, name='TaxAmount', namespace='cbc', default=0.00)
+    subtotals = fields.One2Many(TaxSubTotal, namespace='cac')
+
+
+class AllowanceCharge(model.Model):
+    __name__ = 'AllowanceCharge'
+
+    amount = fields.Many2One(Amount, namespace='cbc')
+    is_discount = fields.Virtual(default=False)
+    
+    def isCharge(self):
+        return self.is_discount == False
+
+    def isDiscount(self):
+        return self.is_discount == True
+
+class Taxes:
+    class Scheme:
+        def __init__(self, scheme):
+            self.scheme = scheme
+
+    class Iva(Scheme):
+        def __init__(self, percent):
+            super().__init__('01')
+            self.percent = percent
+
+        def calculate(self, amount):
+            return form.Amount(amount) * form.Amount(self.percent / 100)
+    
+class InvoiceLine(model.Model):
+    __name__ = 'InvoiceLine'
+
+    id = fields.Many2One(ID, namespace='cbc')
+    quantity = fields.Many2One(Quantity, name='InvoicedQuantity', namespace='cbc')
+    taxtotal = fields.Many2One(TaxTotal, namespace='cac')
+    price = fields.Many2One(Price, namespace='cac')
+    amount = fields.Many2One(Amount, name='LineExtensionAmount', namespace='cbc')
+    allowance_charge = fields.One2Many(AllowanceCharge, 'cac')
+    tax_amount = fields.Virtual(getter='get_tax_amount')
+    
+    def __setup__(self):
+        self._taxs = defaultdict(list)
+        self._subtotals = {}
+
+    def add_tax(self, tax):
+        if not isinstance(tax, Taxes.Scheme):
+            raise ValueError('tax expected TaxIva')
+
+        # inicialiamos subtotal para impuesto
+        if not tax.scheme in self._subtotals:
+            subtotal = self.taxtotal.subtotals.create()
+            subtotal.scheme = tax.scheme
+            
+            self._subtotals[tax.scheme] = subtotal
+        
+        self._taxs[tax.scheme].append(tax)
+
+    def get_tax_amount(self, name, value):
+        total = form.Amount(0)
+        for (scheme, subtotal) in self._subtotals.items():
+            total += subtotal.tax_amount
+
+        return total
+
+    @fields.on_change(['price', 'quantity'])
+    def update_amount(self, name, value):
+        charge = form.AmountCollection(self.allowance_charge)\
+            .filter(lambda charge: charge.isCharge())\
+            .map(lambda charge: charge.amount)\
+            .sum()
+
+        discount = form.AmountCollection(self.allowance_charge)\
+            .filter(lambda charge: charge.isDiscount())\
+            .map(lambda charge: charge.amount)\
+            .sum()
+
+        total = form.Amount(self.quantity)  * form.Amount(self.price)
+        self.amount = total + charge - discount
+        
+        for (scheme, subtotal) in self._subtotals.items():
+            subtotal.tax_amount = 0
+
+        for (scheme, taxes) in self._taxs.items():
+            for tax in taxes:
+                self._subtotals[scheme].tax_amount += tax.calculate(self.amount)
+
+class LegalMonetaryTotal(model.Model):
+    __name__ = 'LegalMonetaryTotal'
+
+    line_extension_amount = fields.Many2One(Amount, name='LineExtensionAmount', namespace='cbc', default=0)
+
+    tax_exclusive_amount = fields.Many2One(Amount, name='TaxExclusiveAmount', namespace='cbc', default=form.Amount(0))
+    tax_inclusive_amount = fields.Many2One(Amount, name='TaxInclusiveAmount', namespace='cbc', default=form.Amount(0))
+    charge_total_amount = fields.Many2One(Amount, name='ChargeTotalAmount', namespace='cbc', default=form.Amount(0))
+    payable_amount = fields.Many2One(Amount, name='PayableAmount', namespace='cbc', default=form.Amount(0))
+
+    @fields.on_change(['tax_inclusive_amount', 'charge_total'])
+    def update_payable_amount(self, name, value):
+        self.payable_amount = self.tax_inclusive_amount + self.charge_total_amount
+
+
+class DIANExtensionContent(model.Model):
+    __name__ = 'ExtensionContent'
+    
+    dian = fields.Many2One(dian.DianExtensions, name='DianExtensions', namespace='sts')
+
+class DIANExtension(model.Model):
+    __name__ = 'UBLExtension'
+
+    content = fields.Many2One(DIANExtensionContent, namespace='ext')
+
+    def __default_get__(self, name, value):
+        return self.content.dian
+
+class UBLExtension(model.Model):
+    __name__ = 'UBLExtension'
+
+    content = fields.Many2One(Element, name='ExtensionContent', namespace='ext', default='')
+    
+class UBLExtensions(model.Model):
+    __name__ = 'UBLExtensions'
+
+    dian = fields.Many2One(DIANExtension, namespace='ext', create=True)
+    extension = fields.Many2One(UBLExtension, namespace='ext', create=True)
+
+class Invoice(model.Model):
+    __name__ = 'Invoice'
+    __namespace__ = fe.NAMESPACES
+
+    _ubl_extensions = fields.Many2One(UBLExtensions, namespace='ext')
+    # nos interesa el acceso solo los atributos de la DIAN
+    dian = fields.Virtual(getter='get_dian_extension')
+    
+    profile_id = fields.Many2One(Element, name='ProfileID', namespace='cbc', default='DIAN 2.1')
+    profile_execute_id = fields.Many2One(Element, name='ProfileExecuteID', namespace='cbc', default='2')
+    
+    id = fields.Many2One(ID, namespace='cbc')
+    issue = fields.Virtual(setter='set_issue')
+    issue_date = fields.Many2One(Date, name='IssueDate', namespace='cbc')
+    issue_time = fields.Many2One(Time, name='IssueTime', namespace='cbc')
+    
+    period = fields.Many2One(Period, name='InvoicePeriod', namespace='cac')
+
+    supplier = fields.Many2One(AccountingSupplierParty, namespace='cac')
+    customer = fields.Many2One(AccountingCustomerParty, namespace='cac')
+    legal_monetary_total = fields.Many2One(LegalMonetaryTotal, namespace='cac')
+    lines = fields.One2Many(InvoiceLine, namespace='cac')
+    
+    taxtotal_01 = fields.Many2One(TaxTotal)
+    taxtotal_04 = fields.Many2One(TaxTotal)
+    taxtotal_03 = fields.Many2One(TaxTotal)
+
+    def __setup__(self):
+        self._namespace_prefix = 'fe'
+        # Se requieren minimo estos impuestos para
+        # validar el cufe
+        self._subtotal_01 = self.taxtotal_01.subtotals.create()
+        self._subtotal_01.scheme = '01'
+        self._subtotal_01.percent = 19.0
+
+        self._subtotal_04 = self.taxtotal_04.subtotals.create()
+        self._subtotal_04.scheme = '04'
+        
+        self._subtotal_03 = self.taxtotal_03.subtotals.create()
+        self._subtotal_03.scheme = '03'
+
+    def cufe(self, token, environment):
+
+        valor_bruto = self.legal_monetary_total.line_extension_amount
+        valor_total_pagar = self.legal_monetary_total.payable_amount
+
+        valor_impuesto_01 = form.Amount(0.0)
+        valor_impuesto_04 = form.Amount(0.0)
+        valor_impuesto_03 = form.Amount(0.0)
+
+        for line in self.lines:
+            for subtotal in line.taxtotal.subtotals:
+                if subtotal.scheme.id == '01':
+                    valor_impuesto_01 += subtotal.tax_amount
+                elif subtotal.scheme.id == '04':
+                    valor_impuesto_04 += subtotal.tax_amount
+                elif subtotal.scheme.id == '03':
+                    valor_impuesto_03 += subtotal.tax_amount
+
+        pattern = [
+            '%s' % str(self.id),
+            '%s' % str(self.issue_date),
+            '%s' % str(self.issue_time),
+            valor_bruto.truncate_as_string(2),
+            '01', valor_impuesto_01.truncate_as_string(2),
+            '04', valor_impuesto_04.truncate_as_string(2),
+            '03', valor_impuesto_03.truncate_as_string(2),
+            valor_total_pagar.truncate_as_string(2),
+            str(self.supplier.party.id),
+            str(self.customer.party.id),
+            str(token),
+            str(environment)
+        ]
+
+        cufe = "".join(pattern)
+        h = hashlib.sha384()
+        h.update(cufe.encode('utf-8'))
+        return h.hexdigest()
+
+    @fields.on_change(['lines'])
+    def update_legal_monetary_total(self, name, value):
+        self.legal_monetary_total.line_extension_amount = 0
+        self.legal_monetary_total.tax_inclusive_amount = 0
+
+        for line in self.lines:
+            self.legal_monetary_total.line_extension_amount += line.amount
+            self.legal_monetary_total.tax_inclusive_amount += line.amount + line.tax_amount
+
+    def set_issue(self, name, value):
+        if not isinstance(value, datetime):
+            raise ValueError('expected type datetime')
+        self.issue_date = value.date()
+        self.issue_time = value
+
+    def get_dian_extension(self, name, _value):
+        return self._ubl_extensions.dian
+
+    def to_xml(self, **kw):
+        # al generar documento el namespace
+        # se hace respecto a la raiz
+        return super().to_xml(**kw)\
+            .replace("fe:", "")\
+            .replace("xmlns:fe", "xmlns")
diff --git a/facho/fe/model/common.py b/facho/fe/model/common.py
new file mode 100644
index 0000000..fa875ee
--- /dev/null
+++ b/facho/fe/model/common.py
@@ -0,0 +1,90 @@
+import facho.model as model
+import facho.model.fields as fields
+
+from datetime import date, datetime
+
+__all__ = ['Element', 'PartyName', 'Name', 'Date', 'Time', 'Period', 'ID', 'Address', 'Country', 'Contact']
+
+class Element(model.Model):
+    """
+    Lo usuamos para elementos que solo manejan contenido
+    """
+    __name__ = 'Element'
+
+class Name(model.Model):
+    __name__ = 'Name'
+
+class Date(model.Model):
+    __name__ = 'Date'
+
+    def __default_set__(self, value):
+        if isinstance(value, str):
+            return value
+        if isinstance(value, date):
+            return value.isoformat()
+
+    def __str__(self):
+        return str(self._value)
+
+class Time(model.Model):
+    __name__ = 'Time'
+
+    def __default_set__(self, value):
+        if isinstance(value, str):
+            return value
+        if isinstance(value, date):
+            return value.strftime('%H:%M:%S-05:00')
+
+    def __str__(self):
+        return str(self._value)
+
+class Period(model.Model):
+    __name__ = 'Period'
+
+    start_date = fields.Many2One(Date, name='StartDate', namespace='cbc')
+
+    end_date = fields.Many2One(Date, name='EndDate', namespace='cbc')
+
+class ID(model.Model):
+    __name__ = 'ID'
+
+    def __default_get__(self, name, value):
+        return self._value
+
+    def __str__(self):
+        return str(self._value)
+
+
+class Country(model.Model):
+    __name__ = 'Country'
+
+    name = fields.Many2One(Element, name='Name', namespace='cbc')
+
+class Address(model.Model):
+    __name__ = 'Address'
+
+    #DIAN 1.7.-2020: FAJ08
+    #DIAN 1.7.-2020: CAJ09
+    id = fields.Many2One(Element, name='ID', namespace='cbc')
+
+    #DIAN 1.7.-2020: FAJ09
+    #DIAN 1.7.-2020: CAJ10
+    city = fields.Many2One(Element, name='CityName', namespace='cbc')
+    
+
+class PartyName(model.Model):
+    __name__ = 'PartyName'
+    
+    name = fields.Many2One(Name, namespace='cbc')
+
+    def __default_set__(self, value):
+        self.name = value
+        return value
+
+    def __default_get__(self, name, value):
+        return self.name
+
+class Contact(model.Model):
+    __name__ = 'Contact'
+
+    email = fields.Many2One(Name, name='ElectronicEmail', namespace='cbc')
diff --git a/facho/fe/model/dian.py b/facho/fe/model/dian.py
new file mode 100644
index 0000000..dbbe3c2
--- /dev/null
+++ b/facho/fe/model/dian.py
@@ -0,0 +1,58 @@
+import facho.model as model
+import facho.model.fields as fields
+from .common import *
+
+class DIANElement(Element):
+    """
+    Elemento que contiene atributos por defecto.
+    
+    Puede extender esta clase y modificar los atributos nuevamente
+    """
+    __name__ = 'DIANElement'
+    
+    scheme_id = fields.Attribute('schemeID', default='4')
+    scheme_name = fields.Attribute('schemeName', default='31')
+    scheme_agency_name = fields.Attribute('schemeAgencyName', default='CO, DIAN (Dirección de Impuestos y Aduanas Nacionales)')
+    scheme_agency_id = fields.Attribute('schemeAgencyID', default='195')
+    
+class SoftwareProvider(model.Model):
+    __name__ = 'SoftwareProvider'
+
+    provider_id = fields.Many2One(Element, name='ProviderID', namespace='sts')
+    software_id = fields.Many2One(Element, name='SoftwareID', namespace='sts')
+
+class InvoiceSource(model.Model):
+    __name__ = 'InvoiceSource'
+
+    identification_code = fields.Many2One(Element, name='IdentificationCode', namespace='sts', default='CO')
+    
+class AuthorizedInvoices(model.Model):
+    __name__ = 'AuthorizedInvoices'
+
+    prefix = fields.Many2One(Element, name='Prefix', namespace='sts')
+    from_range = fields.Many2One(Element, name='From', namespace='sts')
+    to_range = fields.Many2One(Element, name='To', namespace='sts')
+    
+class InvoiceControl(model.Model):
+    __name__ = 'InvoiceControl'
+
+    authorization = fields.Many2One(Element, name='InvoiceAuthorization', namespace='sts')
+    period = fields.Many2One(Period, name='AuthorizationPeriod', namespace='sts')
+    invoices = fields.Many2One(AuthorizedInvoices, namespace='sts')
+
+class AuthorizationProvider(model.Model):
+    __name__ = 'AuthorizationProvider'
+
+
+    id = fields.Many2One(DIANElement, name='AuthorizationProviderID', namespace='sts', default='800197268')
+    
+class DianExtensions(model.Model):
+    __name__ = 'DianExtensions'
+
+    authorization_provider = fields.Many2One(AuthorizationProvider, namespace='sts', create=True)
+
+    software_security_code = fields.Many2One(Element, name='SoftwareSecurityCode', namespace='sts')
+    software_provider = fields.Many2One(SoftwareProvider, namespace='sts')
+    source = fields.Many2One(InvoiceSource, namespace='sts')
+    control = fields.Many2One(InvoiceControl, namespace='sts')
+
diff --git a/facho/model/__init__.py b/facho/model/__init__.py
new file mode 100644
index 0000000..dc3bfaf
--- /dev/null
+++ b/facho/model/__init__.py
@@ -0,0 +1,175 @@
+from .fields import Field
+from collections import defaultdict
+
+class ModelMeta(type):
+    def __new__(cls, name, bases, ns):
+        new = type.__new__(cls, name, bases, ns)
+
+        # mapeamos asignacion en declaracion de clase
+        # a attributo de objeto
+        if '__name__' in ns:
+            new.__name__ = ns['__name__']
+        if '__namespace__' in ns:
+            new.__namespace__ = ns['__namespace__']
+        else:
+            new.__namespace__ = {}
+            
+        return new
+
+class ModelBase(object, metaclass=ModelMeta):
+
+    def __new__(cls, *args, **kwargs):
+        obj = super().__new__(cls, *args, **kwargs)
+        obj._xml_attributes = {}
+        obj._fields = {}
+        obj._value = None
+        obj._namespace_prefix = None
+        obj._on_change_fields = defaultdict(list)
+        obj._order_fields = []
+        
+        def on_change_fields_for_function():
+            # se recorre arbol de herencia buscando attributo on_changes
+            for parent_cls in type(obj).__mro__:
+                for parent_attr in dir(parent_cls):
+                    parent_meth = getattr(parent_cls, parent_attr, None)
+                    if not callable(parent_meth):
+                        continue
+                    on_changes = getattr(parent_meth, 'on_changes', None)
+                    if on_changes:
+                        return (parent_meth, on_changes)
+            return (None, [])
+
+        # forzamos registros de campos al modelo
+        # al instanciar
+        for (key, v) in type(obj).__dict__.items():
+            if isinstance(v, fields.Field):
+                obj._order_fields.append(key)
+
+            if isinstance(v, fields.Attribute) or isinstance(v, fields.Many2One) or isinstance(v, fields.Function) or isinstance(v, fields.Amount):
+                if hasattr(v, 'default') and v.default is not None:
+                    setattr(obj, key, v.default)
+                if hasattr(v, 'create') and v.create == True:
+                    setattr(obj, key, '')
+
+                # register callbacks for changes
+                (fun, on_change_fields) = on_change_fields_for_function()
+                for field in on_change_fields:
+                    obj._on_change_fields[field].append(fun)
+
+
+        # post inicializacion del objeto
+        obj.__setup__()
+        return obj
+
+    def _set_attribute(self, field, name, value):
+        self._xml_attributes[field] = (name, value)
+
+    def __setitem__(self, key, val):
+        self._xml_attributes[key] = val
+
+    def __getitem__(self, key):
+        return self._xml_attributes[key]
+
+    def _get_field(self, name):
+        return self._fields[name]
+
+    def _set_field(self, name, field):
+        field.name = name
+        self._fields[name] = field
+
+    def _set_content(self, value):
+        default = self.__default_set__(value)
+        if default is not None:
+            self._value = default
+
+    def to_xml(self):
+        """
+        Genera xml del modelo y sus relaciones
+        """
+        def _hook_before_xml():
+            self.__before_xml__()
+            for field in self._fields.values():
+                if hasattr(field, '__before_xml__'):
+                    field.__before_xml__()
+                    
+        _hook_before_xml()
+
+        tag = self.__name__
+        ns = ''
+        if self._namespace_prefix is not None:
+            ns = "%s:" % (self._namespace_prefix)
+
+        pair_attributes = ["%s=\"%s\"" % (k, v) for (k, v) in self._xml_attributes.values()]
+
+        for (prefix, url) in self.__namespace__.items():
+            pair_attributes.append("xmlns:%s=\"%s\"" % (prefix, url))
+        attributes = ""
+        if pair_attributes:
+            attributes = " " + " ".join(pair_attributes)
+
+        content = ""
+
+        ordered_fields = {}
+        for name in self._order_fields:
+            if name in self._fields:
+                ordered_fields[name] = True
+            else:
+                for key in self._fields.keys():
+                    if key.startswith(name):
+                        ordered_fields[key] = True
+
+        for name in ordered_fields.keys():
+            value = self._fields[name]
+            # al ser virtual no adicinamos al arbol xml
+            if hasattr(value, 'virtual') and value.virtual:
+                continue
+
+            if hasattr(value, 'to_xml'):
+                content += value.to_xml()
+            elif isinstance(value, str):
+                content += value
+
+        if self._value is not None:
+            content += str(self._value)
+
+        if content == "":
+            return "<%s%s%s/>" % (ns, tag, attributes)
+        else:
+            return "<%s%s%s>%s</%s%s>" % (ns, tag, attributes, content, ns, tag)
+
+    def __str__(self):
+        return self.to_xml()
+
+
+class Model(ModelBase):
+    """
+    Model clase que representa el modelo
+    """
+
+    def __before_xml__(self):
+        """
+        Ejecuta antes de generar el xml, este
+        metodo sirve para realizar actualizaciones
+        en los campos en el ultimo momento
+        """
+        pass
+
+    def __default_set__(self, value):
+        """
+        Al asignar un valor al modelo atraves de una relacion (person.relation = '33')
+        se puede personalizar como hacer esta asignacion.
+        """
+        return value
+
+    def __default_get__(self, name, value):
+        """
+        Al obtener el valor atraves de una relacion (age = person.age)
+        Retorno de valor por defecto
+        """
+        return value
+
+    def __setup__(self):
+        """
+        Inicializar modelo
+        """
+        
diff --git a/facho/model/fields/__init__.py b/facho/model/fields/__init__.py
new file mode 100644
index 0000000..081f195
--- /dev/null
+++ b/facho/model/fields/__init__.py
@@ -0,0 +1,21 @@
+from .attribute import Attribute
+from .many2one import Many2One
+from .one2many import One2Many
+from .function import Function
+from .virtual import Virtual
+from .field import Field
+from .amount import Amount
+
+__all__ = [Attribute, One2Many, Many2One, Virtual, Field, Amount]
+
+def on_change(fields):
+    from functools import wraps
+    
+    def decorator(func):
+        setattr(func, 'on_changes', fields)
+
+        @wraps(func)
+        def wrapper(self, *arg, **kwargs):
+            return func(self, *arg, **kwargs)
+        return wrapper
+    return decorator
diff --git a/facho/model/fields/amount.py b/facho/model/fields/amount.py
new file mode 100644
index 0000000..6402d88
--- /dev/null
+++ b/facho/model/fields/amount.py
@@ -0,0 +1,35 @@
+from .field import Field
+from collections import defaultdict
+import facho.fe.form as form
+
+class Amount(Field):
+    """
+    Amount representa un campo moneda usando form.Amount
+    """
+
+    def __init__(self, name=None, default=None, precision=6):
+        self.field_name = name
+        self.values = {}
+        self.default = default
+        self.precision = precision
+        
+    def __get__(self, model, cls):
+        if model is None:
+            return self
+        assert self.name is not None
+ 
+        self.__init_value(model)
+        model._set_field(self.name, self)
+        return self.values[model]
+
+    def __set__(self, model, value):
+        assert self.name is not None
+        self.__init_value(model)
+        model._set_field(self.name, self)
+        self.values[model] = form.Amount(value, precision=self.precision)
+
+        self._changed_field(model, self.name, value)
+
+    def __init_value(self, model):
+        if model not in self.values:
+            self.values[model] = form.Amount(self.default or 0)
diff --git a/facho/model/fields/attribute.py b/facho/model/fields/attribute.py
new file mode 100644
index 0000000..383fb2f
--- /dev/null
+++ b/facho/model/fields/attribute.py
@@ -0,0 +1,29 @@
+from .field import Field
+
+class Attribute(Field):
+    """
+    Attribute es un atributo del elemento actual.
+    """
+    
+    def __init__(self, name, default=None):
+        """
+        :param name: nombre del atribute
+        :param default: valor por defecto del attributo
+        """
+        self.attribute = name
+        self.value = default
+        self.default = default
+
+    def __get__(self, inst, cls):
+        if inst is None:
+            return self
+
+        assert self.name is not None
+        return self.value
+
+    def __set__(self, inst, value):
+        assert self.name is not None
+        self.value = value
+        
+        self._changed_field(inst, self.name, value)
+        inst._set_attribute(self.name, self.attribute, value)
diff --git a/facho/model/fields/field.py b/facho/model/fields/field.py
new file mode 100644
index 0000000..7deec60
--- /dev/null
+++ b/facho/model/fields/field.py
@@ -0,0 +1,60 @@
+import warnings
+
+class Field:
+    def __set_name__(self, owner, name, virtual=False):
+        self.name = name
+        self.virtual = virtual
+
+    def __get__(self, inst, cls):
+        if inst is None:
+            return self
+        assert self.name is not None
+        return inst._fields[self.name]
+
+    def __set__(self, inst, value):
+        assert self.name is not None
+        inst._fields[self.name] = value
+
+    def _set_namespace(self, inst, name, namespaces):
+        if name is None:
+            return
+
+        #TODO(bit4bit) aunque las pruebas confirmar
+        #que si se escribe el namespace que es
+        #no ahi confirmacion de declaracion previa del namespace
+
+        inst._namespace_prefix = name
+
+    def _call(self, inst, method, *args):
+        call = getattr(inst, method or '', None)
+
+        if callable(call):
+            return call(*args)
+
+    def _create_model(self, inst, name=None, model=None, attribute=None, namespace=None):
+        try:
+            return inst._fields[self.name]
+        except KeyError:
+            if model is not None:
+                obj = model()
+            else:
+                obj = self.model()
+            if name is not None:
+                obj.__name__ = name
+
+            if namespace:
+                self._set_namespace(obj, namespace, inst.__namespace__)
+            else:
+                self._set_namespace(obj, self.namespace, inst.__namespace__)
+
+            if attribute:
+                inst._fields[attribute] = obj
+            else:
+                inst._fields[self.name] = obj
+
+            return obj
+
+    def _changed_field(self, inst, name, value):
+        for fun in inst._on_change_fields[name]:
+            fun(inst, name, value)
+            
diff --git a/facho/model/fields/function.py b/facho/model/fields/function.py
new file mode 100644
index 0000000..707fd55
--- /dev/null
+++ b/facho/model/fields/function.py
@@ -0,0 +1,36 @@
+from .field import Field
+
+class Function(Field):
+    """
+    Permite modificar el modelo cuando se intenta,
+    obtener el valor de este campo.
+
+    DEPRECATED usar Virtual
+    """
+    def __init__(self, field, getter=None, default=None):
+        self.field = field
+        self.getter = getter
+        self.default = default
+
+    def __get__(self, inst, cls):
+        if inst is None:
+            return self
+        assert self.name is not None
+
+        # si se indica `field` se adiciona
+        # como campo del modelo, esto es
+        # que se serializa a xml
+        inst._set_field(self.name, self.field)
+
+        if self.getter is not None:
+            value = self._call(inst, self.getter, self.name, self.field)
+
+            if value is not None:
+                self.field.__set__(inst, value)
+
+        return self.field
+
+    def __set__(self, inst, value):
+        inst._set_field(self.name, self.field)
+        self._changed_field(inst, self.name, value)
+        self.field.__set__(inst, value)
diff --git a/facho/model/fields/many2one.py b/facho/model/fields/many2one.py
new file mode 100644
index 0000000..966d4d2
--- /dev/null
+++ b/facho/model/fields/many2one.py
@@ -0,0 +1,62 @@
+from .field import Field
+from collections import defaultdict
+
+class Many2One(Field):
+    """
+    Many2One describe una relacion pertenece a.
+    """
+
+    def __init__(self, model, name=None, setter=None, namespace=None, default=None, virtual=False, create=False):
+        """
+        :param model: nombre del modelo destino
+        :param name: nombre del elemento xml
+        :param setter: nombre de methodo usado cuando se asigna usa como asignacion ejemplo model.relation = 3
+        :param namespace: sufijo del namespace al que pertenece el elemento
+        :param default: el valor o contenido por defecto
+        :param virtual: se crea la relacion por no se ve reflejada en el xml final
+        :param create: fuerza la creacion del elemento en el xml, ya que los elementos no son creados sino tienen contenido
+        """
+        self.model = model
+        self.setter = setter
+        self.namespace = namespace
+        self.field_name = name
+        self.default = default
+        self.virtual = virtual
+        self.relations = defaultdict(dict)
+        self.create = create
+
+    def __get__(self, inst, cls):
+        if inst is None:
+            return self
+        assert self.name is not None
+
+        if self.name in self.relations:
+            value = self.relations[inst][self.name]
+        else:
+            value = self._create_model(inst, name=self.field_name)
+        self.relations[inst][self.name] = value
+
+        # se puede obtener directamente un valor indicado por el modelo
+        if hasattr(value, '__default_get__'):
+            return value.__default_get__(self.name, value)
+        elif hasattr(inst, '__default_get__'):
+            return inst.__default_get__(self.name, value)
+        else:
+            return value
+        
+    def __set__(self, inst, value):
+        assert self.name is not None
+        inst_model = self._create_model(inst, name=self.field_name, model=self.model)
+        self.relations[inst][self.name] = inst_model
+
+        # si hay setter manual se ejecuta
+        # de lo contrario se asigna como texto del elemento
+        setter = getattr(inst, self.setter or '', None)
+        if callable(setter):
+            setter(inst_model, value)
+        else:
+            inst_model._set_content(value)
+            
+        self._changed_field(inst, self.name, value)
+
+
diff --git a/facho/model/fields/one2many.py b/facho/model/fields/one2many.py
new file mode 100644
index 0000000..8f7f339
--- /dev/null
+++ b/facho/model/fields/one2many.py
@@ -0,0 +1,86 @@
+from .field import Field
+from collections import defaultdict
+
+# TODO(bit4bit) lograr que isinstance se aplique
+# al objeto envuelto
+class _RelationProxy():
+    def __init__(self, obj, inst, attribute):
+        self.__dict__['_obj'] = obj
+        self.__dict__['_inst'] = inst
+        self.__dict__['_attribute'] = attribute
+
+    def __getattr__(self, name):
+        if (name in self.__dict__):
+            return self.__dict__[name]
+
+        rel = getattr(self.__dict__['_obj'], name)
+        if hasattr(rel, '__default_get__'):
+            return rel.__default_get__(name, rel)
+
+        return rel
+
+    def __setattr__(self, attr, value):
+        # TODO(bit4bit) hacemos proxy al sistema de notificacion de cambios
+        # algo burdo, se usa __dict__ para saltarnos el __getattr__ y evitar un fallo por recursion
+        rel = getattr(self.__dict__['_obj'], attr)
+        if hasattr(rel, '__default_set__'):
+            response = setattr(self._obj, attr, rel.__default_set__(value))
+        else:
+            response = setattr(self._obj, attr, value)
+
+        for fun in self.__dict__['_inst']._on_change_fields[self.__dict__['_attribute']]:
+            fun(self.__dict__['_inst'], self.__dict__['_attribute'], value)
+        return response
+
+class _Relation():
+    def __init__(self, creator, inst, attribute):
+        self.creator = creator
+        self.inst = inst
+        self.attribute = attribute
+        self.relations = []
+
+    def create(self):
+        n_relations = len(self.relations)
+        attribute = '%s_%d' % (self.attribute, n_relations)
+        relation = self.creator(attribute)
+        proxy = _RelationProxy(relation, self.inst, self.attribute)
+
+        self.relations.append(relation)
+        return proxy
+
+    def __len__(self):
+        return len(self.relations)
+
+    def __iter__(self):
+        for relation in self.relations:
+            yield relation
+
+class One2Many(Field):
+    """
+    One2Many describe una relacion tiene muchos.
+    """
+
+    def __init__(self, model, name=None, namespace=None, default=None):
+        """
+        :param model: nombre del modelo destino
+        :param name: nombre del elemento xml cuando se crea hijo
+        :param namespace: sufijo del namespace al que pertenece el elemento
+        :param default: el valor o contenido por defecto
+        """
+        self.model = model
+        self.field_name = name
+        self.namespace = namespace
+        self.default = default
+        self.relation = {}
+        
+    def __get__(self, inst, cls):
+        assert self.name is not None
+
+        def creator(attribute):
+            return self._create_model(inst, name=self.field_name, model=self.model, attribute=attribute, namespace=self.namespace)
+        
+        if inst in self.relation:
+            return self.relation[inst]
+        else:
+            self.relation[inst] = _Relation(creator, inst, self.name)
+            return self.relation[inst]
diff --git a/facho/model/fields/virtual.py b/facho/model/fields/virtual.py
new file mode 100644
index 0000000..e39b9dd
--- /dev/null
+++ b/facho/model/fields/virtual.py
@@ -0,0 +1,54 @@
+from .field import Field
+
+# Un campo virtual
+# no participa del renderizado
+# pero puede interactura con este
+class Virtual(Field):
+    """
+    Virtual es un campo que no es renderizado en el xml final
+    """
+    def __init__(self,
+                 setter=None,
+                 getter='',
+                 default=None,
+                 update_internal=False):
+        """
+        :param setter: nombre de methodo usado cuando se asigna usa como asignacion ejemplo model.relation = 3
+        :param getter: nombre del metodo usando cuando se obtiene, ejemplo: valor = mode.relation
+        :param default: valor por defecto
+        :param update_internal: indica que cuando se asigne algun valor este se almacena localmente
+        """
+        self.default = default
+        self.setter = setter
+        self.getter = getter
+        self.values = {}
+        self.update_internal = update_internal
+        self.virtual = True
+
+    def __get__(self, inst, cls):
+        if inst is None:
+            return self
+        assert self.name is not None
+
+        value = self.default
+        try:
+            value = self.values[inst]
+        except KeyError:
+            pass
+
+        try:
+            self.values[inst] = getattr(inst, self.getter)(self.name, value)
+        except AttributeError:
+            self.values[inst] = value
+
+        return self.values[inst]
+    
+    def __set__(self, inst, value):
+        if self.update_internal:
+            inst._value = value
+
+        if self.setter is None:
+            self.values[inst] = value
+        else:
+            self.values[inst] = self._call(inst, self.setter, self.name, value)
+        self._changed_field(inst, self.name, value)        
diff --git a/setup.py b/setup.py
index 226c7f8..185a93a 100644
--- a/setup.py
+++ b/setup.py
@@ -84,6 +84,10 @@ setup(
     test_suite='tests',
     tests_require=test_requirements,
     url='https://github.com/bit4bit/facho',
+<<<<<<< HEAD
     version='0.2.0',
+=======
+    version='0.2.1',
+>>>>>>> morfo
     zip_safe=False,
 )
diff --git a/tests/test_model.py b/tests/test_model.py
new file mode 100644
index 0000000..831460e
--- /dev/null
+++ b/tests/test_model.py
@@ -0,0 +1,601 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+# This file is part of facho.  The COPYRIGHT file at the top level of
+# this repository contains the full copyright notices and license terms.
+
+"""Tests for `facho` package."""
+
+import pytest
+
+import facho.model
+import facho.model.fields as fields
+
+def test_model_to_element():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+    person = Person()
+
+    assert "<Person/>" == person.to_xml()
+
+def test_model_to_element_with_attribute():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+        id = fields.Attribute('id')
+        
+    person = Person()
+    person.id =  33
+
+    personb = Person()
+    personb.id = 44
+
+    assert "<Person id=\"33\"/>" == person.to_xml()
+    assert "<Person id=\"44\"/>" == personb.to_xml()
+
+def test_model_to_element_with_attribute_as_element():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+        
+        id = fields.Many2One(ID)
+
+    person = Person()
+    person.id = 33
+    assert "<Person><ID>33</ID></Person>" == person.to_xml()
+
+def test_many2one_with_custom_attributes():
+    class TaxAmount(facho.model.Model):
+        __name__ = 'TaxAmount'
+
+        currencyID = fields.Attribute('currencyID')
+        
+    class TaxTotal(facho.model.Model):
+        __name__ = 'TaxTotal'
+
+        amount = fields.Many2One(TaxAmount)
+
+    tax_total = TaxTotal()
+    tax_total.amount = 3333
+    tax_total.amount.currencyID = 'COP'
+    assert '<TaxTotal><TaxAmount currencyID="COP">3333</TaxAmount></TaxTotal>' == tax_total.to_xml()
+
+def test_many2one_with_custom_setter():
+
+    class PhysicalLocation(facho.model.Model):
+        __name__ = 'PhysicalLocation'
+
+        id = fields.Attribute('ID')
+        
+    class Party(facho.model.Model):
+        __name__ = 'Party'
+
+        location = fields.Many2One(PhysicalLocation, setter='location_setter')
+
+        def location_setter(self, field, value):
+            field.id = value
+            
+    party = Party()
+    party.location = 99
+    assert '<Party><PhysicalLocation ID="99"/></Party>' == party.to_xml()
+
+def test_many2one_always_create():
+    class Name(facho.model.Model):
+        __name__ = 'Name'
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        name = fields.Many2One(Name, default='facho')
+
+    person = Person()
+    assert '<Person><Name>facho</Name></Person>' == person.to_xml()
+
+def test_many2one_nested_always_create():
+    class Name(facho.model.Model):
+        __name__ = 'Name'
+
+    class Contact(facho.model.Model):
+        __name__ = 'Contact'
+
+        name = fields.Many2One(Name, default='facho')
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        contact = fields.Many2One(Contact, create=True)
+
+    person = Person()
+    assert '<Person><Contact><Name>facho</Name></Contact></Person>' == person.to_xml()
+
+def test_many2one_auto_create():
+    class TaxAmount(facho.model.Model):
+        __name__ = 'TaxAmount'
+
+        currencyID = fields.Attribute('currencyID')
+        
+    class TaxTotal(facho.model.Model):
+        __name__ = 'TaxTotal'
+
+        amount = fields.Many2One(TaxAmount)
+
+    tax_total = TaxTotal()
+    tax_total.amount.currencyID = 'COP'
+    tax_total.amount = 3333
+    assert '<TaxTotal><TaxAmount currencyID="COP">3333</TaxAmount></TaxTotal>' == tax_total.to_xml()
+
+def test_field_model():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        id = fields.Many2One(ID)
+
+    person = Person()
+    person.id = ID()
+    person.id = 33
+    assert "<Person><ID>33</ID></Person>" == person.to_xml()
+
+def test_field_multiple_model():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        id = fields.Many2One(ID)
+        id2 = fields.Many2One(ID)
+
+    person = Person()
+    person.id = 33
+    person.id2 = 44
+    assert "<Person><ID>33</ID><ID>44</ID></Person>" == person.to_xml()
+
+def test_field_model_failed_initialization():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        id = fields.Many2One(ID)
+
+
+    person = Person()
+    person.id = 33
+    assert "<Person><ID>33</ID></Person>" == person.to_xml()
+
+def test_field_model_with_custom_name():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        id = fields.Many2One(ID, name='DID')
+
+
+    person = Person()
+    person.id = 33
+    assert "<Person><DID>33</DID></Person>" == person.to_xml()
+
+def test_field_model_default_initialization_with_attributes():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+
+        reference = fields.Attribute('REFERENCE')
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        id = fields.Many2One(ID)
+
+    person = Person()
+    person.id = 33
+    person.id.reference = 'haber'
+    assert '<Person><ID REFERENCE="haber">33</ID></Person>' == person.to_xml()
+
+def test_model_with_xml_namespace():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+        __namespace__ = {
+            'facho': 'http://lib.facho.cyou'
+        }
+
+    person = Person()
+    assert '<Person xmlns:facho="http://lib.facho.cyou"/>'
+
+def test_model_with_xml_namespace_nested():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+        __namespace__ = {
+            'facho': 'http://lib.facho.cyou'
+        }
+
+        id = fields.Many2One(ID, namespace='facho')
+        
+    person = Person()
+    person.id = 33
+    assert '<Person xmlns:facho="http://lib.facho.cyou"><facho:ID>33</facho:ID></Person>' == person.to_xml()
+
+def test_model_with_xml_namespace_nested_nested():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+        
+    class Party(facho.model.Model):
+        __name__ = 'Party'
+
+        id = fields.Many2One(ID, namespace='party')
+
+        def __default_set__(self, value):
+            self.id = value
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+        __namespace__ = {
+            'person': 'http://lib.facho.cyou',
+            'party': 'http://lib.facho.cyou'
+        }
+
+        id = fields.Many2One(Party, namespace='person')
+        
+    person = Person()
+    person.id = 33
+    assert '<Person xmlns:person="http://lib.facho.cyou" xmlns:party="http://lib.facho.cyou"><person:Party><party:ID>33</party:ID></person:Party></Person>' == person.to_xml()
+
+def test_model_with_xml_namespace_nested_one_many():
+    class Name(facho.model.Model):
+        __name__ = 'Name'
+
+    class Contact(facho.model.Model):
+        __name__ = 'Contact'
+
+        name = fields.Many2One(Name, namespace='contact')
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+        __namespace__ = {
+            'facho': 'http://lib.facho.cyou',
+            'contact': 'http://lib.facho.cyou'
+        }
+
+        contacts = fields.One2Many(Contact, namespace='facho')
+        
+    person = Person()
+    contact = person.contacts.create()
+    contact.name = 'contact1'
+
+    contact = person.contacts.create()
+    contact.name = 'contact2'
+
+    assert '<Person xmlns:facho="http://lib.facho.cyou" xmlns:contact="http://lib.facho.cyou"><facho:Contact><contact:Name>contact1</contact:Name></facho:Contact><facho:Contact><contact:Name>contact2</contact:Name></facho:Contact></Person>' == person.to_xml()
+
+def test_field_model_with_namespace():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+        __namespace__ = {
+            "facho": "http://lib.facho.cyou" 
+        }
+        id = fields.Many2One(ID, namespace="facho")
+
+
+    person = Person()
+    person.id = 33
+    assert '<Person xmlns:facho="http://lib.facho.cyou"><facho:ID>33</facho:ID></Person>' == person.to_xml()
+
+def test_field_hook_before_xml():
+    class Hash(facho.model.Model):
+        __name__ = 'Hash'
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Many2One(Hash)
+
+        def __before_xml__(self):
+            self.hash = "calculate"
+            
+    person = Person()
+    assert "<Person><Hash>calculate</Hash></Person>" == person.to_xml()
+
+
+def test_field_function_with_attribute():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Function(fields.Attribute('hash'), getter='get_hash')
+
+        def get_hash(self, name, field):
+            return 'calculate'
+        
+    person = Person()
+    assert '<Person hash="calculate"/>'
+
+def test_field_function_with_model():
+    class Hash(facho.model.Model):
+        __name__ = 'Hash'
+
+        id = fields.Attribute('id')
+        
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Function(fields.Many2One(Hash), getter='get_hash')
+
+        def get_hash(self, name, field):
+            field.id = 'calculate'
+
+        
+    person = Person()
+    assert person.hash.id == 'calculate'
+    assert '<Person/>'
+   
+
+def test_field_function_setter():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Attribute('hash')
+        password = fields.Virtual(setter='set_hash')
+
+        def set_hash(self, name, value):
+            self.hash = "%s+2" % (value)
+
+    person = Person()
+    person.password = 'calculate'
+    assert '<Person hash="calculate+2"/>' == person.to_xml()
+
+def test_field_function_only_setter():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Attribute('hash')
+        password = fields.Virtual(setter='set_hash')
+
+        def set_hash(self, name, value):
+            self.hash = "%s+2" % (value)
+
+    person = Person()
+    person.password = 'calculate'
+    assert '<Person hash="calculate+2"/>' == person.to_xml()
+    
+def test_model_set_default_setter():
+    class Hash(facho.model.Model):
+        __name__ = 'Hash'
+
+        def __default_set__(self, value):
+            return "%s+3" % (value)
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Many2One(Hash)
+
+    person = Person()
+    person.hash = 'hola'
+    assert '<Person><Hash>hola+3</Hash></Person>' == person.to_xml()
+
+
+def test_field_virtual():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        age = fields.Virtual()
+
+    person = Person()
+    person.age = 55
+    assert person.age == 55
+    assert "<Person/>" == person.to_xml()
+
+
+def test_field_inserted_default_attribute():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Attribute('hash', default='calculate')
+
+
+    person = Person()
+    assert '<Person hash="calculate"/>' == person.to_xml()
+
+def test_field_function_inserted_default_attribute():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Function(fields.Attribute('hash'), default='calculate')
+
+    person = Person()
+    assert '<Person hash="calculate"/>' == person.to_xml()
+
+def test_field_inserted_default_many2one():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+
+        key = fields.Attribute('key')
+        
+        def __default_set__(self, value):
+            self.key = value
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        id = fields.Many2One(ID, default="oe")
+
+    person = Person()
+    assert '<Person><ID key="oe"/></Person>' == person.to_xml()
+
+def test_field_inserted_default_nested_many2one():
+    class ID(facho.model.Model):
+        __name__ = 'ID'
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        id = fields.Many2One(ID, default="ole")
+
+    person = Person()
+    assert '<Person><ID>ole</ID></Person>' == person.to_xml()
+
+def test_model_on_change_field():
+    class Hash(facho.model.Model):
+        __name__ = 'Hash'
+
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        react = fields.Attribute('react')
+        hash = fields.Many2One(Hash)
+
+        @fields.on_change(['hash'])
+        def on_change_react(self, name, value):
+            assert name == 'hash'
+            self.react = "%s+4" % (value)
+
+    person = Person()
+    person.hash = 'hola'
+    assert '<Person react="hola+4"><Hash>hola</Hash></Person>' == person.to_xml()
+
+def test_model_on_change_field_attribute():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        react = fields.Attribute('react')
+        hash = fields.Attribute('Hash')
+
+        @fields.on_change(['hash'])
+        def on_react(self, name, value):
+            assert name == 'hash'
+            self.react = "%s+4" % (value)
+
+    person = Person()
+    person.hash = 'hola'
+    assert '<Person react="hola+4" Hash="hola"/>' == person.to_xml()
+
+def test_model_one2many():
+    class Line(facho.model.Model):
+        __name__ = 'Line'
+
+        quantity = fields.Attribute('quantity')
+        
+    class Invoice(facho.model.Model):
+        __name__ = 'Invoice'
+
+        lines = fields.One2Many(Line)
+
+    invoice = Invoice()
+    line = invoice.lines.create()
+    line.quantity = 3
+    line = invoice.lines.create()
+    line.quantity = 5
+    assert '<Invoice><Line quantity="3"/><Line quantity="5"/></Invoice>' == invoice.to_xml()
+
+
+def test_model_one2many_with_on_changes():
+    class Line(facho.model.Model):
+        __name__ = 'Line'
+
+        quantity = fields.Attribute('quantity')
+        
+    class Invoice(facho.model.Model):
+        __name__ = 'Invoice'
+
+        lines = fields.One2Many(Line)
+        count = fields.Attribute('count', default=0)
+        
+        @fields.on_change(['lines'])
+        def refresh_count(self, name, value):
+            self.count = len(self.lines)
+
+    invoice = Invoice()
+    line = invoice.lines.create()
+    line.quantity = 3
+    line = invoice.lines.create()
+    line.quantity = 5
+
+    assert len(invoice.lines) == 2
+    assert '<Invoice count="2"><Line quantity="3"/><Line quantity="5"/></Invoice>' == invoice.to_xml()
+
+def test_model_one2many_as_list():
+    class Line(facho.model.Model):
+        __name__ = 'Line'
+
+        quantity = fields.Attribute('quantity')
+        
+    class Invoice(facho.model.Model):
+        __name__ = 'Invoice'
+
+        lines = fields.One2Many(Line)
+
+    invoice = Invoice()
+    line = invoice.lines.create()
+    line.quantity = 3
+    line = invoice.lines.create()
+    line.quantity = 5
+
+    lines = list(invoice.lines)
+    assert len(list(invoice.lines)) == 2
+
+    for line in lines:
+        assert isinstance(line, Line)
+    assert '<Invoice><Line quantity="3"/><Line quantity="5"/></Invoice>' == invoice.to_xml()
+
+
+def test_model_attributes_order():
+    class Line(facho.model.Model):
+        __name__ = 'Line'
+
+        quantity = fields.Attribute('quantity')
+        
+    class Invoice(facho.model.Model):
+        __name__ = 'Invoice'
+
+        line1 = fields.Many2One(Line, name='Line1')
+        line2 = fields.Many2One(Line, name='Line2')
+        line3 = fields.Many2One(Line, name='Line3')
+
+
+    invoice = Invoice()
+    invoice.line2.quantity = 2
+    invoice.line3.quantity = 3
+    invoice.line1.quantity = 1
+
+    assert '<Invoice><Line1 quantity="1"/><Line2 quantity="2"/><Line3 quantity="3"/></Invoice>' == invoice.to_xml()
+
+
+def test_field_amount():
+    class Line(facho.model.Model):
+        __name__ = 'Line'
+
+        amount = fields.Amount(name='Amount', precision=1)
+        amount_as_attribute = fields.Attribute('amount')
+
+        @fields.on_change(['amount'])
+        def on_amount(self, name, value):
+            self.amount_as_attribute = self.amount
+
+    line = Line()
+    line.amount = 33
+
+    assert '<Line amount="33.0"/>' == line.to_xml()
+        
+
+def test_model_setup():
+    class Line(facho.model.Model):
+        __name__ = 'Line'
+
+        amount = fields.Attribute(name='amount')
+
+        def __setup__(self):
+            self.amount = 23
+
+    line = Line()
+    assert '<Line amount="23"/>' == line.to_xml()
diff --git a/tests/test_model_invoice.py b/tests/test_model_invoice.py
new file mode 100644
index 0000000..f4b98df
--- /dev/null
+++ b/tests/test_model_invoice.py
@@ -0,0 +1,119 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+# This file is part of facho.  The COPYRIGHT file at the top level of
+# this repository contains the full copyright notices and license terms.
+
+"""Nuevo esquema para modelar segun decreto"""
+
+from datetime import datetime
+
+import pytest
+from lxml import etree
+import facho.fe.model as model
+import facho.fe.form as form
+from facho import fe
+import helpers
+
+def simple_invoice():
+    invoice = model.Invoice()
+    invoice.dian.software_security_code = '12345'
+    invoice.dian.software_provider.provider_id = 'provider-id'
+    invoice.dian.software_provider.software_id = 'facho'
+    invoice.dian.control.prefix = 'SETP'
+    invoice.dian.control.from_range =  '1000'
+    invoice.dian.control.to_range = '1000'
+    invoice.id = '323200000129'
+    invoice.issue = datetime.strptime('2019-01-16 10:53:10-05:00', '%Y-%m-%d %H:%M:%S%z')
+    invoice.supplier.party.id = '700085371'
+    invoice.customer.party.id = '800199436'
+
+    line = invoice.lines.create()
+    line.add_tax(model.Taxes.Iva(19.0))
+
+    # TODO(bit4bit) acoplamiento temporal
+    # se debe crear primero el subotatl
+    # para poder calcularse al cambiar el precio
+    line.quantity = 1
+    line.price = 1_500_000
+
+    return invoice
+
+def test_simple_invoice_cufe():
+    token = '693ff6f2a553c3646a063436fd4dd9ded0311471'
+    environment = fe.AMBIENTE_PRODUCCION
+    invoice = simple_invoice()
+    assert invoice.cufe(token, environment) == '8bb918b19ba22a694f1da11c643b5e9de39adf60311cf179179e9b33381030bcd4c3c3f156c506ed5908f9276f5bd9b4'
+
+def test_simple_invoice_sign_dian(monkeypatch):
+    invoice = simple_invoice()
+
+    xmlstring = invoice.to_xml()
+    p12_data = open('./tests/example.p12', 'rb').read()
+    signer = fe.DianXMLExtensionSigner.from_bytes(p12_data)
+
+    with monkeypatch.context() as m:
+        helpers.mock_urlopen(m)
+        xmlsigned = signer.sign_xml_string(xmlstring)
+    assert "Signature" in xmlsigned
+
+
+def test_dian_extension_authorization_provider():
+    invoice = simple_invoice()
+    xml = fe.FeXML.from_string(invoice.to_xml())
+    provider_id = xml.get_element('/fe:Invoice/ext:UBLExtensions/ext:UBLExtension/ext:ExtensionContent/sts:DianExtensions/sts:AuthorizationProvider/sts:AuthorizationProviderID')
+
+    assert provider_id.attrib['schemeID'] == '4'
+    assert provider_id.attrib['schemeName'] == '31'
+    assert provider_id.attrib['schemeAgencyName'] == 'CO, DIAN (Dirección de Impuestos y Aduanas Nacionales)'
+    assert provider_id.attrib['schemeAgencyID'] == '195'
+    assert provider_id.text == '800197268'
+
+def test_invoicesimple_xml_signed_using_fexml(monkeypatch):
+    invoice = simple_invoice()
+
+    xml = fe.FeXML.from_string(invoice.to_xml())
+
+    signer = fe.DianXMLExtensionSigner('./tests/example.p12')
+
+    print(xml.tostring())
+    with monkeypatch.context() as m:
+        import helpers
+        helpers.mock_urlopen(m)
+        xml.add_extension(signer)
+
+    elem = xml.get_element('/fe:Invoice/ext:UBLExtensions/ext:UBLExtension[2]/ext:ExtensionContent/ds:Signature')
+    assert elem.text is not None
+
+def test_invoice_supplier_party():
+    invoice = simple_invoice()
+    invoice.supplier.party.name = 'superfacho'
+    invoice.supplier.party.tax_scheme.registration_name = 'legal-superfacho'
+    invoice.supplier.party.contact.email = 'superfacho@etrivial.net'
+    
+    xml = fe.FeXML.from_string(invoice.to_xml())
+
+    name = xml.get_element('/fe:Invoice/cac:AccountingSupplierParty/cac:Party/cac:PartyName/cbc:Name')
+    assert name.text == 'superfacho'
+
+    name = xml.get_element('/fe:Invoice/cac:AccountingSupplierParty/cac:Party/cac:PartyTaxScheme/cbc:RegistrationName')
+    assert name.text == 'legal-superfacho'
+
+    name = xml.get_element('/fe:Invoice/cac:AccountingSupplierParty/cac:Party/cac:Contact/cbc:ElectronicEmail')
+    assert name.text == 'superfacho@etrivial.net'
+
+def test_invoice_customer_party():
+    invoice = simple_invoice()
+    invoice.customer.party.name = 'superfacho-customer'
+    invoice.customer.party.tax_scheme.registration_name = 'legal-superfacho-customer'
+    invoice.customer.party.contact.email = 'superfacho@etrivial.net'
+
+    xml = fe.FeXML.from_string(invoice.to_xml())
+
+    name = xml.get_element('/fe:Invoice/cac:AccountingCustomerParty/cac:Party/cac:PartyName/cbc:Name')
+    assert name.text == 'superfacho-customer'
+
+    name = xml.get_element('/fe:Invoice/cac:AccountingCustomerParty/cac:Party/cac:PartyTaxScheme/cbc:RegistrationName')
+    assert name.text == 'legal-superfacho-customer'
+
+    name = xml.get_element('/fe:Invoice/cac:AccountingCustomerParty/cac:Party/cac:Contact/cbc:ElectronicEmail')
+    assert name.text == 'superfacho@etrivial.net'