Chage AstToSqlAlchemyClauseVisitor to accept {namespace: entity} di…

…cts as requested in issue gorilla-co#24

odata_query/sqlalchemy/sqlalchemy_clause.py

@@ -1,6 +1,6 @@
 import operator
 from collections.abc import Collection
-from typing import Any, Callable, List, Optional, Type, Union
+from typing import Any, Callable, List, Optional, Type, Union, Dict
 
 from sqlalchemy.inspection import inspect
 from sqlalchemy.orm.attributes import InstrumentedAttribute
@@ -38,34 +38,45 @@ class AstToSqlAlchemyClauseVisitor(visitor.NodeVisitor):
     filter clause.
 
     Args:
-        root_model: The root model of the query.
+        root_model: The root model of the query. It can be either a single
+        sqlalchemy ORM entity, a collection of entities, or a dict mapping
+        namespace to entities.
     """
 
     def __init__(
-        self, root_model: Union[Type[DeclarativeMeta], List[Type[DeclarativeMeta]]]
+        self,
+        root_model: Union[
+            Type[DeclarativeMeta],
+            List[Type[DeclarativeMeta]],
+            Dict[str, Type[DeclarativeMeta]],
+        ],
     ):
-        if not isinstance(root_model, Collection):
-            root_model = [root_model]
-        self._models = {model.__name__: model for model in root_model}
+        if isinstance(root_model, dict):
+            self._models = root_model
+        else:
+            if not isinstance(root_model, Collection):
+                root_model = [root_model]
+            self._models = {model.__name__: model for model in root_model}
         self._models_set = {model.__name__ for model in root_model}
         self.join_relationships: List[InstrumentedAttribute] = []
 
     def visit_Identifier(self, node: ast.Identifier) -> ColumnClause:
         ":meta private:"
-        # check if the namespace is listed
-        namespaces = self._models_set.intersection(node.namespace)
-        for namespace in namespaces:
-            try:
-                return getattr(self._models[namespace], node.name)
-            except AttributeError:
-                # This is probably a hard error...
-                pass
-        # Check all the models. Duplicate names are are an issue
-        for model in self._models.values():
-            try:
-                return getattr(model, node.name)
-            except AttributeError:
-                pass
+
+        if node.namespace:
+            namespaces = self._models_set.intersection(node.namespace)
+            for namespace in namespaces:
+                try:
+                    return getattr(self._models[namespace], node.name)
+                except AttributeError:
+                    pass
+        else:
+            # Check all the models. Duplicate names are an issue
+            for model in self._models.values():
+                try:
+                    return getattr(model, node.name)
+                except AttributeError:
+                    pass
         raise ex.InvalidFieldException(node.name)
 
     def visit_Attribute(self, node: ast.Attribute) -> ColumnClause: