Values in nested api model are null

[aklehm]

Hello,
I hope you can help me.
Im using python 3.9.0, Flask 1.1.2, flask-restplus 0.13.0, Flask_SQLAlchemy2.4.4 and SQLAlchemy 1.3.20.

I have a problem with a nested api model, which looks like this:

lightstate = api.model('LightState', {
    'red': fields.Integer(attribute='red', description='red part of the rgb light'),
    'green': fields.Integer(attribute='green', description='green part of the rgb light'),
    'blue': fields.Integer(attribute='blue', description='blue part of the rgb light'),
    'bri': fields.Integer(attribute='bri', description='brightness of the light')    
})
lights = api.model('Lights',{
    'id': fields.Integer(readOnly=True, description='The database id of the light'),
    'name': fields.String(required=True, description='light name'),
    'state': fields.Nested(lightstate)
})

This is my my request handler:

namespace = api.namespace('light'')

@namespace.route('/')
class Light(Resource):
    @api.marshal_with(lights)
    def get(self):
        light_data = Lights.query.all()
        return light_data

And my dto:

db = SQLAlchemy()

class Lights(db.Model):
    __bind_key__ = 'lights'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(255))
    red = db.Column(db.Integer)
    green = db.Column(db.Integer)
    blue = db.Column(db.Integer)
    bri = db.Column(db.Integer)

    def __init__(self, name, red, green, blue, bri):
        self.name = name
        self.red = red
        self.green = green
        self.blue = blue
        self.bri = bri

If I send a request, I'm getting this response with null values:

[
  {
    "id": 1,
    "name": "garden",
    "state": {
      "red": null,
      "green": null,
      "blue": null,
      "bri": null
    }
  },
  {
    "id": 2,
    "name": "pool",
    "state": {
      "red": null,
      "green": null,
      "blue": null,
      "bri": null
    }
  }
]

But if I remove the nested field from my api model 'lights' and add all fields, the values are not null.

lights = api.model('Lights', {
    'id': fields.Integer(readOnly=True, description='The database id of the light'),
    'name': fields.String(required=True, description='light name'),
    'red': fields.Integer(description='red part of the rgb light'),
    'green': fields.Integer(description='green part of the rgb light'),
    'blue': fields.Integer(description='blue part of the rgb light'),
    'bri': fields.Integer(description='brightness of the light')
})

[
  {
    "id": 1,
    "name": "garden",
    "red": 50,
    "green": 205,
    "blue": 50,
    "bri": 84
  },
  {
    "id": 2,
    "name": "pool",
    "red": 255,
    "green": 42,
    "blue": 255,
    "bri": 96
  }
]

I want to use the nested fields. How do I get the values in my response?

Thanks in advance

[KaiveYoung]

lights = api.model('Lights',{
  'id': fields.Integer(readOnly=True, description='The database id of the light'),
  'name': fields.String(required=True, description='light name'),
  'state': fields.Nested(lightstate,attribute=lambda x:x)
})

[aklehm]

Thanks for your answer. I will try.