model: reword error messages for assoc. sets

I want to print out precise messages, so I needed to replace the
standard dict with my very own implementation called Declarations
because otherwise I would have to add try..except everywhere. The class
Declarations just overwrites the method __getitem__ (the operator square
braces []) where I catch the KeyError exception and raise my own
KeyError exception with an appropriate message.

Author: filak-sap

pyodata/v2/model.py

@@ -560,10 +560,18 @@ def add_complex_type(self, ctype):
             collection_type_name = 'Collection({})'.format(ctype.name)
             self.complex_types[collection_type_name] = Collection(ctype.name, ctype)
 
+    class Declarations(dict):
+
+        def __getitem__(self, key):
+            try:
+                return super(Schema.Declarations, self).__getitem__(key)
+            except KeyError:
+                raise KeyError('There is no Schema Namespace {}'.format(key))
+
     def __init__(self):
         super(Schema, self).__init__()
 
-        self._decls = dict()
+        self._decls = Schema.Declarations()
 
     def __str__(self):
         return "{0}({1})".format(self.__class__.__name__, ','.join(self.namespaces))
@@ -725,13 +733,14 @@ def association_set_by_association(self, association_name, namespace=None):
             for association_set in list(self._decls[namespace].association_sets.values()):
                 if association_set.association_type.name == association_name:
                     return association_set
-            raise KeyError('Association set with association type {} does not exist in namespace {}'.format(
+            raise KeyError('Association Set for Association {} does not exist in Schema Namespace {}'.format(
                 association_name, namespace))
         for decl in list(self._decls.values()):
             for association_set in list(decl.association_sets.values()):
                 if association_set.association_type.name == association_name:
                     return association_set
-        raise KeyError('Association set with association type {} does not exist'.format(association_name))
+        raise KeyError('Association Set for Association {} does not exist in any Schema Namespace'.format(
+            association_name))
 
     def association_set(self, set_name, namespace=None):
         if namespace is not None:

tests/test_model_v2.py

@@ -204,6 +204,21 @@ def test_edmx_associations(schema):
     association_set = schema.association_set_by_association('CustomerOrders')
     assert str(association_set) == 'AssociationSet(CustomerOrder_AssocSet)'
 
+    # error handling: without namespace
+    with pytest.raises(KeyError) as typ_ex_info:
+        assert schema.association_set_by_association('FooBar')
+    assert typ_ex_info.value.args[0] == 'Association Set for Association FooBar does not exist in any Schema Namespace'
+
+    # error handling: with unknown namespace
+    with pytest.raises(KeyError) as typ_ex_info:
+        assert schema.association_set_by_association('FooBar', namespace='BLAH')
+    assert typ_ex_info.value.args[0] == 'There is no Schema Namespace BLAH'
+
+    # error handling: with namespace
+    with pytest.raises(KeyError) as typ_ex_info:
+        assert schema.association_set_by_association('FooBar', namespace='EXAMPLE_SRV')
+    assert typ_ex_info.value.args[0] == 'Association Set for Association FooBar does not exist in Schema Namespace EXAMPLE_SRV'
+
 
 def test_edmx_navigation_properties(schema):
     """Test parsing of navigation properties"""