Make a Relay ConnectionField optimized to work with Query

[Fedalto]

Graphene has the graphene.relay.ConnectionField, which slices a list/iterable to build the edges inside the Relay connection.
But it doesn't play well with DB queries. It calls len() with Query doesn't have.

graphene-sqlalchemy should have a implementation of the ConnectionField that is aware of the sqlalchemy's Query and use it to slice directly in the DB.

For now, I'm using this workaround:

class RelayConnectionField(graphene.relay.ConnectionField):
    @classmethod
    def resolve_connection(cls, connection_type, args, resolved):
        if isinstance(resolved, Query):
            len_ = resolved.count()
            connection = connection_from_list_slice(
                resolved,
                args,
                connection_type=connection_type,
                edge_type=connection_type.Edge,
                pageinfo_type=PageInfo,
                slice_start=0,
                list_length=len_,
                list_slice_length=len_,
            )
            connection.iterable = resolved
            return connection
        else:
            return super().resolve_connection(connection_type, args, resolved)

[Fedalto]

Similar/same issue to graphql-python/graphene#589

[sebastiandev]

Isn't this already covered here ?

    @classmethod
    def connection_resolver(cls, resolver, connection, model, root, info, **args):
        iterable = resolver(root, info, **args)
        if iterable is None:
            iterable = cls.get_query(model, info, **args)
        if isinstance(iterable, Query):
            _len = iterable.count()
        else:
            _len = len(iterable)

[Fedalto]

Indeed it is.
But if I used it I receives an error here

graphene-sqlalchemy/graphene_sqlalchemy/fields.py

Lines 26 to 28 in 4827ce2

	assert issubclass(_type, SQLAlchemyObjectType), (
	"SQLAlchemyConnectionField only accepts SQLAlchemyObjectType types"
	)

as I'm sending a graphene.relay.Connection instead of a SQLAlchemyObjectType.
Maybe I'm using it incorrectly?

[sebastiandev]

Yeah you need a SQLAlchemyObjectType there, everything gets down to an ObjectType eventually
Show us your Query definition to have a better idea of whats going on

[Fedalto]

Following graphene 2.0 (https://github.com/graphql-python/graphene/blob/master/UPGRADE-v2.0.md#node-connections), I defined explicit Connections.
My code is very similar to the one described in the link:

class User(SQLAlchemyObjectType):
    class Meta:
        model = UserModel
    name = String()

class UserConnection(relay.Connection):
    class Meta:
        node = User

class Group(SQLAlchemyObjectType):
    class Meta:
        model = GroupModel
    # Here, it works with the RelayConnectionField I posted in the issue.
    # But breaks if I change to SQLAlchemyConnectionField
    user_connection = RelayConnectionField(UserConnection)

class Query(ObjectType):
    group = Field(Group)

It does, however, work if I send the SQLAlchemyObjectType directly, like

user_connection = SQLAlchemyConnectionField(User)

But how can I add custom data to the Connection itself?

[sebastiandev]

You are mixing RelayConnectionFields with SqlAlchemy, You have to extend from SQLAlchemyConnectionField. I cant take a look right now, but check this as here we add fields to connections for counting purposes:
#58 (comment)

[Fedalto]

@sebastiandev, thanks for the help.

SQLAlchemyConnectionField indeed does handle the Query.
My issue now is how to subclass a Connection to add custom data to it.
Seems a duplicate of #65 (and there's a PR to fix it already #94).
I'm closing this.

[github-actions]

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