Can I perform recursive queries?

[davidsims9t]

I have a database with a hierarchical recursive structure. This is what my schema looks like:

@schema.register
class HierarchyChild(SQLAlchemyNode):
    class Meta:
        model = HierarchyModel

@schema.register
class Hierarchy(SQLAlchemyNode):
    class Meta:
        model = HierarchyModel

    children = SQLAlchemyConnectionField(HierarchyChild)

Currently this returns nested results, however, it doesn't pass the parent context to the child node. Thanks in advanced!

[cliedeman]

Hi David

I had the same issue implementing a viewer pattern and then trying to use the parent context to filter child relations.

The root object is omitted from the call

As a workaround you can subclass SQLAlchemyConnectionField and replace the connection_resolver method with one that passes the root to the get_query method.

The current pattern I use is to override get_query and apply all my custom filters and ordering.

@syrusakbary Would you be open to a PR that added the root to the get query method?

Ciaran

[davidsims9t]

Thanks @cliedeman, I'll give that a try. Do you have an example of how to do this? I'm new to using Python.

[cliedeman]

from graphene.relay.connection import PageInfo
from graphql_relay.connection.arrayconnection import connection_from_list_slice

import graphene
from graphene import relay
from graphene_sqlalchemy import SQLAlchemyConnectionField, SQLAlchemyObjectType

class UserActivitiesConnectionField(SQLAlchemyConnectionField):
    def __init__(self):
        super().__init__(Activity)

    @classmethod
    def connection_resolver(cls, resolver, connection, model, root, args, context, info):
        """
        Override Default method so that we can pass the root to the get_query method
        """
        iterable = resolver(root, args, context, info)
        if iterable is None:
            iterable = cls.get_query(model, root, context, info, args)
        if isinstance(iterable, Query):
            _len = iterable.count()
        else:
            _len = len(iterable)
        return connection_from_list_slice(
            iterable,
            args,
            slice_start=0,
            list_length=_len,
            list_slice_length=_len,
            connection_type=connection,
            pageinfo_type=PageInfo,
            edge_type=connection.Edge,
        )

    # noinspection PyMethodOverriding
    @classmethod
    def get_query(cls, model: db_model.Activity, root: db_model.User, context, info, args):
        if not root:
            return []
        query.filter(model.user_id == root.id)
        return query

class User(SQLAlchemyObjectType):
    class Meta:
        model = db_model.User
        interfaces = (relay.Node,)

Where Activity is some nested graphql object that needs the root

[davidsims9t]

@cliedeman Thanks for posting this. I ended up using upgrading to graphene 1.0 and using a lambda function to create a recursive nested relational ship on my Hierarchy schema.

[cliedeman]

Glad you got it working
Would you mind pasting a sample for future readers?

[davidsims9t]

Sure thing. It was pretty simple actually. So I just used:

class Hierarchy(SQLAlchemyObjectType):
    class Meta:
        model = HierarchyModel
        interfaces = (relay.Node, )

    children = SQLAlchemyConnectionField(lambda: Hierarchy)

    def resolve_children(self, args, context, info):
        return HierarchyModel.query.filter(HierarchyModel.parent_tsn.in_([self.tsn])).all()

If I use just use Hierarchy without using lambda, Hierarchy is undefined.

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