Stricter non-null fields for relationships

graphene_sqlalchemy/converter.py

@@ -59,6 +59,39 @@
 
 is_selectin_available = getattr(strategies, "SelectInLoader", None)
 
+"""
+Flag for whether to generate stricter non-null fields for many-relationships.
+
+For many-relationships, both the list element and the list field itself will be
+non-null by default. This better matches ORM semantics, where there is always a
+list for a many relationship (even if it is empty), and it never contains None.
+
+This option can be set to False to revert to pre-3.0 behavior.
+
+For example, given a User model with many Comments:
+
+    class User(Base):
+        comments = relationship("Comment")
+
+The Schema will be:
+
+    type User {
+        comments: [Comment!]!
+    }
+
+When set to False, the pre-3.0 behavior gives:
+
+    type User {
+        comments: [Comment]
+    }
+"""
+use_non_null_many_relationships = True
+
+
+def set_non_null_many_relationships(non_null_flag):
+    global use_non_null_many_relationships
+    use_non_null_many_relationships = non_null_flag
+
 
 def get_column_doc(column):
     return getattr(column, "doc", None)
@@ -160,7 +193,14 @@ def _convert_o2m_or_m2m_relationship(
     )
 
     if not child_type._meta.connection:
-        return graphene.Field(graphene.List(child_type), **field_kwargs)
+        # check if we need to use non-null fields
+        list_type = (
+            graphene.NonNull(graphene.List(graphene.NonNull(child_type)))
+            if use_non_null_many_relationships
+            else graphene.List(child_type)
+        )
+
+        return graphene.Field(list_type, **field_kwargs)
 
     # TODO Allow override of connection_field_factory and resolver via ORMField
     if connection_field_factory is None:

graphene_sqlalchemy/tests/test_converter.py

@@ -21,6 +21,7 @@
     convert_sqlalchemy_hybrid_method,
     convert_sqlalchemy_relationship,
     convert_sqlalchemy_type,
+    set_non_null_many_relationships,
 )
 from ..fields import UnsortedSQLAlchemyConnectionField, default_connection_field_factory
 from ..registry import Registry, get_global_registry
@@ -71,6 +72,16 @@ class Model(declarative_base()):
     )
 
 
+@pytest.fixture
+def use_legacy_many_relationships():
+    set_non_null_many_relationships(False)
+    try:
+        yield
+    finally:
+        set_non_null_many_relationships(True)
+
+
+
 def test_hybrid_prop_int():
     @hybrid_property
     def prop_method() -> int:
@@ -501,6 +512,30 @@ class Meta:
         True,
         "orm_field_name",
     )
+    # field should be [A!]!
+    assert isinstance(dynamic_field, graphene.Dynamic)
+    graphene_type = dynamic_field.get_type()
+    assert isinstance(graphene_type, graphene.Field)
+    assert isinstance(graphene_type.type, graphene.NonNull)
+    assert isinstance(graphene_type.type.of_type, graphene.List)
+    assert isinstance(graphene_type.type.of_type.of_type, graphene.NonNull)
+    assert graphene_type.type.of_type.of_type.of_type == A
+
+
+@pytest.mark.usefixtures("use_legacy_many_relationships")
+def test_should_manytomany_convert_connectionorlist_list_legacy():
+    class A(SQLAlchemyObjectType):
+        class Meta:
+            model = Pet
+
+    dynamic_field = convert_sqlalchemy_relationship(
+        Reporter.pets.property,
+        A,
+        default_connection_field_factory,
+        True,
+        "orm_field_name",
+    )
+    # field should be [A]
     assert isinstance(dynamic_field, graphene.Dynamic)
     graphene_type = dynamic_field.get_type()
     assert isinstance(graphene_type, graphene.Field)

graphene_sqlalchemy/tests/test_types.py

@@ -331,8 +331,10 @@ class Meta:
 
     pets_field = ReporterType._meta.fields["pets"]
     assert isinstance(pets_field, Dynamic)
-    assert isinstance(pets_field.type().type, List)
-    assert pets_field.type().type.of_type == PetType
+    assert isinstance(pets_field.type().type, NonNull)
+    assert isinstance(pets_field.type().type.of_type, List)
+    assert isinstance(pets_field.type().type.of_type.of_type, NonNull)
+    assert pets_field.type().type.of_type.of_type.of_type == PetType
     assert pets_field.type().description == "Overridden"