Nested fields with mashmallow_sqlalchemy and flask_marshmallow - flask-sqlalchemy

Question

I am trying to get a nested serialized output, but all I get is the 'many' side of the many-to-one's table's primary key.
Expected output:
[{'part_numbers':
{'part_number': '23103048', 'description': 'blue product'},
'machines': 2,
'percent_complete': 5.0,
'serial_number': '001',
'timestamp_created': 2020-03-12T15:4:23.135098},
{'part_numbers':
{'part_number': '44444009', 'description': 'red product'},
'machines': 1,
'percent_complete': 60.0,
'serial_number': '002',
'timestamp_created': '2020-03-12T15:44:23.135098'}]
Actual output:
[{'id': 3,
'machines': 2,
'percent_complete': 5.0,
'serial_number': '001',
'timestamp_created': 2020-03-12T15:4:23.135098},
{'id': 1,
'machines': 1,
'percent_complete': 60.0,
'serial_number': '0002',
'timestamp_created': '2020-03-12T15:44:23.135098'}]
These are my files. I have tried adding part_numbers = ma.Nested(PartNumbers) to the Machine schema inside models.py, but it didn't change the result!
my_app
|--- my_app
|--- \__init\__.py
|--- models.py
|--- views.py
models.py
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
from marshmallow_sqlalchemy import SQLAlchemyAutoSchema
db = SQLAlchemy()
ma = Marshmallow()
### Models ###
class Machine(db.Model):
id = db.Column(db.Integer, primary_key=True)
serial_number = db.Column(db.Text, unique=True)
percent_complete = db.Column(db.Float)
part_number_id = db.Column(db.Integer, db.ForeignKey('PartNumbers.id'))
timestamp_created = db.Column(db.DateTime, default=datetime.utcnow)
class PartNumbers(db.Model):
__tablename__ = 'PartNumbers'
id = db.Column(db.Integer, primary_key=True)
part_number = db.Column(db.Text, unique=True)
description = db.Column(db.Text)
machines = db.relationship('Machines', backref='machines', lazy='dynamic')
### Schemas ###
class PartNumbersSchema(SQLAlchemyAutoSchema):
class Meta:
model = PartNumbers
include_fk = True
class MachineSchema(SQLAlchemyAutoSchema):
class Meta:
model = Machines
include_relationships = True
__init__.py
from flask import Flask
from .models import db, ma
from .views import my_app
app = Flask(__name__)
db.init_app(app)
ma.init_app(app)
app.register_blueprint(my_app)
views.py
from flask import Blueprint
from .models import db, Machines, MachineSchema, PartNumbers
my_app = Blueprint("my_app", __name__)
machines_schema = MachineSchema(many=True)
#my_app.route('/')
def home()
machines = db.session.query(Machines).all()
return machines_schema.dump(machines)

Answer 1

Define part_number in the Machine class:
class Machine(db.Model):
id = db.Column(db.Integer, primary_key=True)
serial_number = db.Column(db.Text, unique=True)
percent_complete = db.Column(db.Float)
part_number_id = db.Column(db.Integer, db.ForeignKey('PartNumbers.id'))
timestamp_created = db.Column(db.DateTime, default=datetime.utcnow)
part_numbers = db.relationship('PartNumbers')
You have to define part_numbers in the MachineSchema explicitly:
from marshmallow_sqlalchemy import fields
class MachineSchema(SQLAlchemyAutoSchema):
class Meta:
model = Machines
part_numbers = fields.Nested(PartNumbersSchema)
I assumed part_numbers is a single object (1:1 relationship). Otherwise, you have to add many=True to part_numbers.
More details: https://marshmallow.readthedocs.io/en/stable/nesting.html
[edited to incorporate correction in comment]