Add model relation field

Author: rmk135

domain_models/fields.py

@@ -111,3 +111,21 @@ def _converter(self, value):
         if not isinstance(value, datetime.datetime):
             raise TypeError('{0} is not valid date and time')
         return value
+
+
+class Model(Field):
+    """Model relation field."""
+
+    def __init__(self, related_model_cls, default=None):
+        """Initializer."""
+        super(Model, self).__init__(default=default)
+
+        self.related_model_cls = related_model_cls
+
+    def _converter(self, value):
+        """Convert raw input value of the field."""
+        if not isinstance(value, self.related_model_cls):
+            raise TypeError('{0} is not valid model instance, instance of '
+                            '{1} required'.format(value,
+                                                  self.related_model_cls))
+        return value

tests/test_fields.py

@@ -11,6 +11,10 @@
 from domain_models import errors
 
 
+class RelatedModel(model.DomainModel):
+    """Example model that is used for testing relations."""
+
+
 class ExampleModel(model.DomainModel):
     """Example model."""
 
@@ -29,6 +33,8 @@ class ExampleModel(model.DomainModel):
     date_field = fields.Date()
     datetime_field = fields.DateTime()
 
+    model_field = fields.Model(RelatedModel)
+
 
 class FieldTest(unittest.TestCase):
     """Base field tests."""
@@ -320,3 +326,34 @@ def test_set_incorrect(self):
 
         with self.assertRaises(TypeError):
             model.datetime_field = some_object
+
+
+class ModelTest(unittest.TestCase):
+    """Date and time field tests."""
+
+    def test_set_value(self):
+        """Test setting of correct value."""
+        model = ExampleModel()
+        related_model = RelatedModel()
+
+        model.model_field = related_model
+
+        self.assertEqual(model.model_field, related_model)
+
+    def test_reset_value(self):
+        """Test resetting of value."""
+        model = ExampleModel()
+        related_model = RelatedModel()
+
+        model.model_field = related_model
+        model.model_field = None
+
+        self.assertIsNone(model.model_field)
+
+    def test_set_incorrect(self):
+        """Test setting of incorrect value."""
+        model = ExampleModel()
+        some_object = object()
+
+        with self.assertRaises(TypeError):
+            model.model_field = some_object