带有 mashmallow_sqlalchemy 和 flask_marshmallow 的嵌套字段

Question

我正在尝试获取嵌套的序列化输出，但我得到的只是多对一表主键的“多”端。

预期输出：

[{'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'}]

实际输出：

[{'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'}]

这些是我的文件。我尝试将part_numbers = ma.Nested(PartNumbers) 添加到Machine 内部models.py 架构中，但它并没有改变结果！

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

1. 在 Machine 类中定义 part_number：

   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')
   

2. 您必须在 MachineSchema 中明确定义 part_numbers：

   from marshmallow_sqlalchemy import fields
   class MachineSchema(SQLAlchemyAutoSchema):
     class Meta:
       model = Machines
     part_numbers = fields.Nested(PartNumbersSchema)
   

我假设 part_numbers 是单个对象（1:1 关系）。否则，您必须将 many=True 添加到 part_numbers。

更多详情：https://marshmallow.readthedocs.io/en/stable/nesting.html

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