Issue with metaclass and Schemas in Nested fields about flask_accepts

[sbrieuc]

I'm noticing that the issue occurs only when using the Schema class and not with an instance.

Does not work:

class Foo(Schema):
    pass

class Bar(SQLAlchemySchema):
    items = fields.Nested(Foo)

Works:

class Foo(Schema):
    pass

class Bar(SQLAlchemySchema):
    items = fields.Nested(Foo())

So I'm not sure of the direction to take here: always providing an instance of the schema will do the trick and we can leave it as it is, but I feel that it's not necessarily the best practice in term of memory usage. What do you think ?

[apryor6]

I totally agree that issubclass would be more suitable and would be more than happy to accept a PR. Just add a test that asserts behavior works as intended if you provide either type of Schema and we should be good to go.