Flask-Restful - Return json with nested array

Question

My model consists in users and books. I want to nest all the books as an array of objects inside each user object, in order to show the books that each user owns. I'm trying to use marshal to nest the books as a list inside the users fields but nothing happens. In the response, there is only the array of users but no track of books and neither of an error. The idea is this:

books_fields = {
    'id': fields.Integer,
    'type' : fields.String,
    'created_at': fields.DateTime,
    'user_id' : fields.Integer
}

users_fields = {
    'id': fields.Integer,
    'name' : fields.String,
    'created_at': fields.DateTime,
    'books': fields.List(fields.Nested(books_fields))
}


users = session.query(model.Users).outerjoin(model.Cities)
         .filter_by(weather = args.weather).all()

for user in users:
    books = session.query(model.Books).outerjoin(model.Users)
             .filter_by(user_id = user.id).all()
    user.books = marshal(books, books_fields)


return {'users': marshal(users, users_fields)}, 200

The issue is that books don't appear.

Answer 1

I believe you need to manually create a dictionary for users. Marshal has never worked for me in this manner (this is assuming your books query is returning rows).

Try something like this:

books_fields = {
    'id': fields.Integer,
    'type' : fields.String,
    'created_at': fields.DateTime,
    'user_id' : fields.Integer
}

users_fields = {
    'id': fields.Integer,
    'name' : fields.String,
    'created_at': fields.DateTime,
    'books': fields.List(fields.Nested(books_fields))
}

users_dict = {}

users = session.query(model.Users).outerjoin(model.Cities)
         .filter_by(weather = args.weather).all()

for user in users:
    books_dict = {}
    books = session.query(model.Books).outerjoin(model.Users)
             .filter_by(user_id = user.id).all()
    for book in books:
        book_dict = {
            'id': book.id,
            'type': book.type,
            'created_at': book.created_at
        }
        books_dict.append(book_dict)

    user_dict = {
        'id': user.id,
        'name': user.name,
        'created_at': user.created_at,
        'books': books_dict
    }
    users_dict.append(user_dict)

return {'users': marshal(users_dict, users_fields)}, 200