How to make model flask marshmallow_sqlalchemy desrialize related object - flask

Question

I have this code:
import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session, sessionmaker, relationship, backref
engine = sa.create_engine("sqlite:///:memory:")
session = scoped_session(sessionmaker(bind=engine))
Base = declarative_base()
class Author(Base):
__tablename__ = "authors"
id = sa.Column(sa.Integer, primary_key=True)
name = sa.Column(sa.String, nullable=False)
books = relationship("Book", backref=backref("author", lazy="joined"),
foreign_keys="Book.author_id", lazy="dynamic")
def __repr__(self):
return "<Author(name={self.name!r})>".format(self=self)
class Book(Base):
__tablename__ = "books"
id = sa.Column(sa.Integer, primary_key=True)
title = sa.Column(sa.String)
author_id = sa.Column(sa.Integer, sa.ForeignKey("authors.id"))
Base.metadata.create_all(engine)
from marshmallow_sqlalchemy import SQLAlchemySchema, auto_field, SQLAlchemyAutoSchema
class AuthorSchema(SQLAlchemyAutoSchema):
class Meta:
model = Author
load_instance = True # Optional: deserialize to model instances
# dump_only = ("id",)
include_fk = True
class BookSchema(SQLAlchemyAutoSchema):
class Meta:
model = Book
load_instance = True
# dump_only = ("id",)
include_fk = True
author = Author(name="Chuck Paluhniuk")
author_schema = AuthorSchema()
book = Book(title="Fight Club", author=author)
book_schema = BookSchema()
session.add(author)
session.add(book)
session.commit()
dump_data_author = author_schema.dump(author)
print(dump_data_author)
dump_data_book = book_schema.dump(book)
print(dump_data_book)
When I run the code it prints:
{'id': 1, 'name': 'Chuck Paluhniuk'}
{'id': 1, 'author_id': 1, 'title': 'Fight Club'}
I want to change the code such that it prints:
{'id': 1, 'name': 'Chuck Paluhniuk', 'books': [{'id': 1, 'author_id': 1, 'title': 'Fight Club'}]}
{'id': 1, 'author_id': 1, 'title': 'Fight Club'}
How should I do this?
I want to have control over deserializing related objects.
I am also curious about some othe settings in the meta such load_only and dump_only and excelude, etc.

Answer 1

In my opinion, it is necessary to define nested fields in order to include relationships in the output in this way. You can define that the relationships are included automatically, but this only applies to the primary keys. In order not to use an override of a field, I have not included the relationships.
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from marshmallow_sqlalchemy import SQLAlchemyAutoSchema
from flask_marshmallow import Marshmallow
app = Flask(__name__)
db = SQLAlchemy(app)
ma = Marshmallow(app)
class Author(db.Model):
__tablename__ = "authors"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, nullable=False)
books = db.relationship("Book",
backref=db.backref("author", lazy="joined"),
foreign_keys="Book.author_id",
lazy="dynamic"
)
class Book(db.Model):
__tablename__ = "books"
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String)
author_id = db.Column(db.Integer, db.ForeignKey("authors.id"))
class BookSchema(SQLAlchemyAutoSchema):
class Meta:
model = Book
include_fk = True
load_instance = True
sqla_session = db.session
class AuthorSchema(SQLAlchemyAutoSchema):
class Meta:
model = Author
load_instance = True
# include_relationships = True # See below
sqla_session = db.session
books = ma.Nested(BookSchema, many=True)
with app.app_context():
db.drop_all()
db.create_all()
author = Author(name="Chuck Paluhniuk")
book = Book(title="Fight Club", author=author)
db.session.add(author)
db.session.add(book)
db.session.commit()
author_schema = AuthorSchema()
book_schema = BookSchema()
dump_data_author = author_schema.dump(author)
print(dump_data_author)
dump_data_book = book_schema.dump(book)
print(dump_data_book)
json = [
{'author_id': 1, 'title': 'Fight Club', 'id': 1}
]
schema = BookSchema(many=True)
print(schema.load(json))
json = [
{'books': [{'author_id': 1, 'title': 'Fight Club', 'id': 1}], 'name': 'Chuck Paluhniuk', 'id': 1}
]
schema = AuthorSchema(many=True)
print(schema.load(json))