Flask-SQLAlchemy and Flask-Restless not fetching grandchildren

flask, flask-restless, flask-sqlalchemy, python, sqlalchemy

Solution

postprocessors can be used to fetch grandchild.

def parent_post_get_many(result=None, search_params=None, **kw):
   for object in result['objects']:
      for child in object['children']:
         grandchild = Grandchild.query.get(child['grand_child_id'])
         child.update({'grandchild': grandchild})

api.create_api(Parent, postprocessors={'GET_MANY': [parent_post_get_many]})

Problem

Problem I am building an app on Flask, Flask-SQLAlchemy, and Flask-Restless. I have used restless to generate an API for a parent-child-grandchild relationship*. A GET on my child will correctly fetch the grandchild, but a GET on the parent will not fetch the grandchild for each child. *In fact, the parent-child relationship is a many-to-many, but same premise. Models ``` class Grandchild(db.Model): id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String, nullable=False) parent = db.relationship('Child', backref='grandchild') parent_child = db.Table('parent_child', db.Column('parent_id', db.Integer, db.ForeignKey('parent.id')), db.Column('child_id', db.Integer, db.ForeignKey('child.id')), db.Column('number', db.SmallInteger) ) class Child(db.Model): id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String, nullable=False) grandchild_id = db.Column(db.Integer, db.ForeignKey('grandchild.id'), nullable=False) class Parent(db.Model): id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String, nullable=False) children = db.relationship('Child', secondary=parent_child) api.create_api(Child, exclude_columns=['grandchild_id']) api.create_api(Parent) ``` GET: /api/child response ``` { "num_results": 1, "objects": [ { "id": 1, "name": "test" "grandchild": { "id": 1, "name": "test" } } ], "page": 1, "total_pages": 1 } ``` GET: /api/parent response ``` { "num_results": 1, "objects": [ { "children": [ { "id": 1, "name": "test", "grandchild_id": 1 } ], "id": 1, "name": "test" }], "page": 1, "total_pages": 1 } ```

Original source