Flask Marshmallow serialize many to many relation with extra field

This schema gives you something quite similar to your specification:

from marshmallow import Schema, fieldsclass InterestSchema(Schema):    class Meta:        fields = ('id', 'name')        ordered = Trueclass OwnerInterestSchema(Schema):    interest = fields.Nested(InterestSchema)    class Meta:        fields = ('id', 'interest', 'active')        ordered = Trueclass OwnerSchema(Schema):    interests = fields.Nested(OwnerInterestSchema, many=True)    class Meta:        fields = ('id', 'name', 'mobile', 'interests')        ordered = True

You can then serialise your data like this (note that my model doesn't have exactly the same name as yours):

>>> from app.serialisation import OwnerSchema>>> from app.models import Owner>>> data = OwnerSchema().dump(Owner.query.get(1))>>> from marshmallow import pprint>>> pprint(data){"id": 1, "name": "John", "mobile": "07123456789", "interests": [{"interest": {"id": 1, "name": "Economics"}, "active": true}, {"interest": {"id": 2, "name": "Poetry"}, "active": true}, {"interest": {"id": 3, "name": "Sport"}, "active": false}]}

Let me just indent that output so you can see what's going on:

{  "id": 1,  "name": "John",  "mobile": "07123456789",  "interests": [    {      "interest": {        "id": 1,        "name": "Economics"      },      "active": true    },    {      "interest": {        "id": 2,        "name": "Poetry"      },      "active": true    },    {      "interest": {        "id": 3,        "name": "Sport"      },      "active": false    }  ]}

You can adapt this to use the model-plus-exclude paradigm if you want. And if you really want that "_embedded" field in your JSON, you probably need a custom field, as described here.

You could also use custom fields to flatten your interests and put the "active" field on the same level as "id" and "name", but I think that would be misleading.