Fixed bug when using a declarative function for the __tablename__

When specifying a function to dynamically define a tablename as a declared
attribute it became impossible to overwrite it using a manually defined name.

Look at the test to see the issue, with the original code this test would fail.

Author: RmStorm

gino/declarative.py

@@ -166,8 +166,9 @@ def _init_table(cls, sub_cls):
                     updates[k] = sub_cls.__attr_factory__(k, v)
                 elif isinstance(v, (sa.Index, sa.Constraint)):
                     inspected_args.append(v)
-        if table_name is None:
-            table_name = getattr(sub_cls, '__tablename__', None)
+        if getattr(sub_cls, '__tablename__', None) and \
+                not callable(getattr(sub_cls, '__tablename__')):
+            table_name = getattr(sub_cls, '__tablename__')
         if table_name is None:
             return
         sub_cls._column_name_map = column_name_map

tests/test_declarative.py

@@ -260,3 +260,20 @@ class Model(db.Model):
         select_col = db.Column(name=db.quoted_name('select', False))
         assert select_col.name == 'select'
         assert not select_col.name.quote
+
+
+async def test_overwrite_declared_table_name():
+    class MyTableNameMixin:
+        @db.declared_attr
+        def __tablename__(cls):
+            return cls.__name__.lower()
+
+    class MyTableWithoutName(MyTableNameMixin, db.Model):
+        id = db.Column(db.Integer, primary_key=True)
+
+    class MyTableWithName(MyTableNameMixin, db.Model):
+        __tablename__ = 'manually_overwritten_name'
+        id = db.Column(db.Integer, primary_key=True)
+
+    assert MyTableWithoutName.__table__.name == 'mytablewithoutname'
+    assert MyTableWithName.__table__.name == 'manually_overwritten_name'