diff --git a/test/test_grpc_models_accessor.py b/test/test_grpc_models_accessor.py
index 3851857..729fac3 100644
--- a/test/test_grpc_models_accessor.py
+++ b/test/test_grpc_models_accessor.py
@@ -18,6 +18,7 @@
 from mock import patch, MagicMock
 from grpc_client.models_accessor import GRPCModelsAccessor
 from grpc_client.resources import RESOURCES
+from grpc_client.KEYS import TOSCA_KEYS
 
 class FakeObj:
     new = None
@@ -34,15 +35,26 @@
 
 mock_resources = {
     'username~pass': {
-        'test-model': FakeResource
+        'test-model': FakeResource,
+        'single-key': FakeResource,
+        'double-key': FakeResource
     }
 }
 
+mock_keys = {
+    'i-do-not-exists': ['name'],
+    'test-model': ['name'],
+    'empty-key': [],
+    'single-key': ['fake_key'],
+    'double-key': ['key_1', 'key_2'],
+}
+
 USERNAME = 'username'
 PASSWORD = 'pass'
 
 class GRPCModelsAccessor_Create_or_update_Test(unittest.TestCase):
 
+    @patch.dict(TOSCA_KEYS, mock_keys, clear=True)
     def test_unkown_user(self):
         """
         [GRPCModelsAccessor] get_model_from_classname: If a user does not have orm classes, raise
@@ -55,6 +67,7 @@
         self.assertEqual(e.exception.message, "[XOS-TOSCA] User 'username' does not have ready resources")
 
     @patch.dict(RESOURCES, mock_resources, clear=True)
+    @patch.dict(TOSCA_KEYS, mock_keys, clear=True)
     def test_unkown_module(self):
         """
         [GRPCModelsAccessor] get_model_from_classname: If a model is not know by the grpc api, raise
@@ -64,35 +77,92 @@
         }
         with self.assertRaises(Exception) as e:
             GRPCModelsAccessor.get_model_from_classname('i-do-not-exists', data, USERNAME, PASSWORD)
-        self.assertEqual(e.exception.message, "[XOS-TOSCA] The model you are trying to create (name: test, class: i-do-not-exists) is not know by xos-core")
+        self.assertEqual(e.exception.message, "[XOS-TOSCA] The model you are trying to create (class: i-do-not-exists, properties, {'name': 'test'}) is not know by xos-core")
+
+    def test_unkown_tosca_key(self):
+        """
+        [GRPCModelsAccessor] get_model_from_classname: If a model does not have a tosca_key, raise
+        """
+        data = {
+            "name": "test"
+        }
+        with self.assertRaises(Exception) as e:
+            GRPCModelsAccessor.get_model_from_classname('no-key', data, USERNAME, PASSWORD)
+        self.assertEqual(e.exception.message, "[XOS-TOSCA] Model no-key doesn't have a tosca_key specified")
+
+    @patch.dict(TOSCA_KEYS, mock_keys, clear=True)
+    def test_empty_tosca_key(self):
+        """
+        [GRPCModelsAccessor] get_model_from_classname: If a model does not have a tosca_key, raise
+        """
+        data = {
+            "name": "test"
+        }
+        with self.assertRaises(Exception) as e:
+            GRPCModelsAccessor.get_model_from_classname('empty-key', data, USERNAME, PASSWORD)
+        self.assertEqual(e.exception.message, "[XOS-TOSCA] Model empty-key doesn't have a tosca_key specified")
+
+    @patch.dict(TOSCA_KEYS, mock_keys, clear=True)
+    def test_tosca_key_are_defined(self):
+        """
+        [GRPCModelsAccessor] get_model_from_classname: a model should have a property for it's tosca_key
+        """
+        data = {
+            "name": "test",
+        }
+        with self.assertRaises(Exception) as e:
+            GRPCModelsAccessor.get_model_from_classname('single-key', data, USERNAME, PASSWORD)
+        self.assertEqual(e.exception.message, "[XOS-TOSCA] Model single-key doesn't have a property for the specified tosca_key ('fake_key')")
 
     @patch.object(FakeResource.objects, "filter")
     @patch.object(FakeResource.objects, "new", MagicMock(return_value=FakeModel))
+    @patch.dict(TOSCA_KEYS, mock_keys, clear=True)
+    def test_composite_key(self, mock_filter):
+        """
+        [GRPCModelsAccessor] get_model_from_classname: should use a composite key to lookup a model
+        """
+        data = {
+            "name": "test",
+            "key_1": "key1",
+            "key_2": "key2"
+        }
+        with patch.dict(RESOURCES, mock_resources, clear=True):
+            model = GRPCModelsAccessor.get_model_from_classname('double-key', data, USERNAME, PASSWORD)
+            mock_filter.assert_called_with(key_1="key1", key_2="key2")
+            self.assertEqual(model, FakeModel)
+
+    @patch.object(FakeResource.objects, "filter")
+    @patch.object(FakeResource.objects, "new", MagicMock(return_value=FakeModel))
+    @patch.dict(TOSCA_KEYS, mock_keys, clear=True)
     def test_new_model(self, mock_filter):
         """
         [GRPCModelsAccessor] get_model_from_classname: should create a new model
         """
         data = {
-            "name": "test"
+            "name": "test",
+            "fake_key": "key"
         }
         with patch.dict(RESOURCES, mock_resources, clear=True):
-            model = GRPCModelsAccessor.get_model_from_classname('test-model', data, USERNAME, PASSWORD)
-            mock_filter.assert_called_with(name="test")
+            model = GRPCModelsAccessor.get_model_from_classname('single-key', data, USERNAME, PASSWORD)
+            mock_filter.assert_called_with(fake_key="key")
             self.assertEqual(model, FakeModel)
 
     @patch.object(FakeResource.objects, "filter", MagicMock(return_value=[FakeExistingModel]))
+    @patch.dict(TOSCA_KEYS, mock_keys, clear=True)
     def test_existing_model(self):
         """
         [GRPCModelsAccessor] get_model_from_classname: should update an existing model
         """
         data = {
-            "name": "test"
+            "name": "test",
+            "fake_key": "key"
         }
         with patch.dict(RESOURCES, mock_resources, clear=True):
-            model = GRPCModelsAccessor.get_model_from_classname('test-model', data, USERNAME, PASSWORD)
+            model = GRPCModelsAccessor.get_model_from_classname('single-key', data, USERNAME, PASSWORD)
             self.assertEqual(model, FakeExistingModel)
 
     @patch.object(FakeResource.objects, "filter", MagicMock(return_value=['a', 'b']))
+    @patch.dict(TOSCA_KEYS, mock_keys, clear=True)
     def test_multiple_models(self):
         """
         [GRPCModelsAccessor] get_model_from_classname: should raise an exception if multiple instances are found
@@ -103,33 +173,7 @@
         with patch.dict(RESOURCES, mock_resources, clear=True):
             with self.assertRaises(Exception) as e:
                 GRPCModelsAccessor.get_model_from_classname('test-model', data, USERNAME, PASSWORD)
-            self.assertEqual(e.exception.message, "[XOS-Tosca] Model test has multiple instances, I can't handle it")
-
-    @patch.dict(RESOURCES, mock_resources, clear=True)
-    @patch.object(FakeResource.objects, "filter")
-    @patch.object(FakeResource.objects, "new")
-    def test_find_model_without_name_property(self, mock_new, mock_filter):
-        """
-        [GRPCModelsAccessor] get_model_from_classname: should lookup a model by the first property
-        """
-        data = {
-            'foo': 'bar',
-            'something': 'else'
-        }
-        GRPCModelsAccessor.get_model_from_classname('test-model', data, USERNAME, PASSWORD)
-        mock_filter.assert_called_with(foo="bar")
-        mock_new.assert_called()
-
-    @patch.dict(RESOURCES, mock_resources, clear=True)
-    @patch.object(FakeResource.objects, "new")
-    def test_model_without_properties(self, mock_new):
-        """
-        [GRPCModelsAccessor] get_model_from_classname: should create a new model if not properties are specified
-        """
-        data = {
-        }
-        GRPCModelsAccessor.get_model_from_classname('test-model', data, USERNAME, PASSWORD)
-        mock_new.assert_called()
+            self.assertEqual(e.exception.message, "[XOS-Tosca] Model of class test-model and properties {'name': 'test'} has multiple instances, I can't handle it")
 
 if __name__ == '__main__':
     unittest.main()
\ No newline at end of file
diff --git a/test/test_tosca_parser_e2e.py b/test/test_tosca_parser_e2e.py
index a4c8e29..87f3cf1 100644
--- a/test/test_tosca_parser_e2e.py
+++ b/test/test_tosca_parser_e2e.py
@@ -220,4 +220,4 @@
         with self.assertRaises(Exception) as e:
             parser.execute()
 
-        self.assertEqual(e.exception.message.message, "[XOS-TOSCA] Model Site:Open Networking Lab has property 'must-exist' but cannot be found")
+        self.assertEqual(e.exception.message.message, "[XOS-TOSCA] Model of class Site and properties {'name': 'Open Networking Lab'} has property 'must-exist' but cannot be found")
diff --git a/test/tosca/link.yaml b/test/tosca/link.yaml
new file mode 100644
index 0000000..f2c000f
--- /dev/null
+++ b/test/tosca/link.yaml
@@ -0,0 +1,160 @@
+
+# Copyright 2017-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+tosca_definitions_version: tosca_simple_yaml_1_0
+
+description: Persist xos-sample-gui-extension
+
+imports:
+  - custom_types/slice.yaml
+  - custom_types/network.yaml
+  - custom_types/networkslice.yaml
+  - custom_types/networktemplate.yaml
+  - custom_types/site.yaml
+  - custom_types/image.yaml
+  - custom_types/service.yaml
+  - custom_types/serviceinstance.yaml
+  - custom_types/serviceinstancelink.yaml
+
+topology_template:
+  node_templates:
+
+    service#mcord:
+      type: tosca.nodes.Service
+      properties:
+        name: mcord
+
+    test1:
+      type: tosca.nodes.ServiceInstance
+      properties:
+        name: test1
+
+    test2:
+      type: tosca.nodes.ServiceInstance
+      properties:
+        name: test2
+
+    link1:
+      type: tosca.nodes.ServiceInstanceLink
+      requirements:
+        - provider_service_instance:
+            node: test1
+            relationship: tosca.relationships.BelongsToOne
+        - subscriber_service_instance:
+            node: test2
+            relationship: tosca.relationships.BelongsToOne
+
+    link2:
+      type: tosca.nodes.ServiceInstanceLink
+      requirements:
+        - subscriber_service:
+            node: service#mcord
+            relationship: tosca.relationships.BelongsToOne
+        - provider_service_instance:
+            node: test2
+            relationship: tosca.relationships.BelongsToOne
+
+    # Site
+    mysite:
+      type: tosca.nodes.Site
+      properties:
+        must-exist: true
+        name: mysite
+
+    # Images
+    image#trusty-server-multi-nic:
+      type: tosca.nodes.Image
+      properties:
+        must-exist: true
+        name: trusty-server-multi-nic
+
+    # slices
+    slice#slice1:
+      type: tosca.nodes.Slice
+      properties:
+        name: mysite_slice1
+      requirements:
+        - site:
+            node: mysite
+            relationship: tosca.relationships.BelongsToOne
+        - default_image:
+            node: image#trusty-server-multi-nic
+            relationship: tosca.relationships.BelongsToOne
+
+    slice#slice2:
+      type: tosca.nodes.Slice
+      properties:
+        name: mysite_slice2
+      requirements:
+        - site:
+            node: mysite
+            relationship: tosca.relationships.BelongsToOne
+        - default_image:
+            node: image#trusty-server-multi-nic
+            relationship: tosca.relationships.BelongsToOne
+
+    # networks
+
+    shared_template:
+      type: tosca.nodes.NetworkTemplate
+      properties:
+        must-exist: true
+        name: shared_template
+
+    network#network1:
+      type: tosca.nodes.Network
+      properties:
+        name: network1
+      requirements:
+        - template:
+            node: shared_template
+            relationship: tosca.relationships.BelongsToOne
+        - owner:
+            node: slice#slice1
+            relationship: tosca.relationships.BelongsToOne
+
+    network#network2:
+      type: tosca.nodes.Network
+      properties:
+        name: network2
+      requirements:
+        - template:
+            node: shared_template
+            relationship: tosca.relationships.BelongsToOne
+        - owner:
+            node: slice#slice2
+            relationship: tosca.relationships.BelongsToOne
+
+    networkslice#slice1_network2:
+      type: tosca.nodes.NetworkSlice
+      requirements:
+        - network:
+            node: network#network2
+            relationship: tosca.relationships.BelongsToOne
+        - slice:
+            node: slice#slice1
+            relationship: tosca.relationships.BelongsToOne
+
+    networkslice#slice2_network1:
+      type: tosca.nodes.NetworkSlice
+      requirements:
+        - network:
+            node: network#network1
+            relationship: tosca.relationships.BelongsToOne
+        - slice:
+            node: slice#slice2
+            relationship: tosca.relationships.BelongsToOne
+