Infinite Loop caused by bidirectional relationships on child objects in included data

[mhxi]

The issue occurs while attempting to load an object with bidirectional relationships on child objects in the included data.

Below is a minimal example demonstrating the issue. When we try to load the root data object, we run into a RecursionError. It seems marshmallow-jsonapi goes into an infinite loop trying to load the included objects when the children have bidirectional relationships.

Simple Example:

from marshmallow_jsonapi import Schema
from marshmallow_jsonapi import fields


class RootSchema(Schema):

    id = fields.Str(required=True)
    baz = fields.Str()

    first_children = fields.Relationship(
        many=True,
        type_='first_children',
        schema='FirstChildSchema'
    )

    class Meta:
        type_ = 'root'


class FirstChildSchema(Schema):

    id = fields.Str(required=True)
    foo = fields.Str()

    root = fields.Relationship(
        many=True,
        type_='root',
        schema='RootSchema'
    )

    second_children = fields.Relationship(
        many=True,
        type_='second_children',
        schema='SecondChildSchema'
    )


    class Meta:
        type_ = 'first_children'

class SecondChildSchema(Schema):

    id = fields.Str(required=True)
    bar = fields.Str()

    first_children = fields.Relationship(
        many=True,
        type_='first_children',
        schema='FirstChildSchema'
    )

    class Meta:
        type_ = 'second_children'


data = {
    'data':{
        'type': 'root',
        'id':'root_id',
        'attributes':{
            'baz': 'qwerty'
        },
        'relationships': {
            'first_children': {
                'data': [{
                    'id': 'firstchild_id',
                    'type': 'first_children'
                }]
            }
        }
    },
    'included': [{
        'id': 'firstchild_id',
        'type':'first_children',
        'attributes':{
            'foo': 'qwerty'
        },
        'relationships': {
            'second_children': {
                'data': [{
                    'id': 'secondchild_id',
                    'type': 'second_children'
                }]
            },
            'root': {
                'id': 'root_id',
                'type': 'root'
            }
        }
    }, {
        'id': 'secondchild_id',
        'type':'second_children',
        'attributes':{
            'bar': 'qwerty'
        },
        'relationships': {
            'first_children': {
                'data': [{
                    'id': 'firstchild_id',
                    'type': 'first_children'
                }]
            }
        }
    }]
}

schema = RootSchema()
print(schema.load(data))

Error:
RecursionError: maximum recursion depth exceeded

python=3.7
marshmallow=3.2.1
marshmallow-jsonapi=0.22.0

[multimeric]

What's strange is that this bug doesn't happen if you remove all references to the SecondChildSchema, even though there's also a circular relationship between Root and FirstChild. It seems that this happens only when there are relationships between multiple included data resources.

I think this is because they access related related data in slightly different ways from when it's the root element that has relationships.

[multimeric]

I've looked into solving this, but it's not easy. The best way would be to store the ret value from Unmarshaller and storing it in a dictionary indexed by id and type, and then look up that dictionary whenever we try to deserialize a field. However the Unmarshaller class doesn't provide any hooks with which we can do this. I think we'd have to modify the base marshmallow library to do this.

[retr0h]

@TMiguelT ever figure this out?