Autogenerating Nested fields by SQLAlchemyAutoSchema

Hi, I’m looking through the new SQLAlchemyAutoSchema and I’m failing to find a way to autogenerate Nested fields based on relationship. Even with include_relationships = True the generated fields appear to be fields.Related, not fields.Nested as I would have guessed. The autogenerating schemas will certainly cleanup my code quite a lot and having the option to generate Nested fields directly would be nice to have. Is such a feature considered? Or is it already included and I’m missing something?

Here’s a a fully runnable example showing the different behavior between schema generated by SQLAlchemyAutoSchema and one with manually added field author = fields.Nested(AuthorSchema). I’m primarily looking for the output of the nested version.

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship, joinedload
from sqlalchemy import Column, Integer, String, ForeignKey
from marshmallow_sqlalchemy import SQLAlchemyAutoSchema, auto_field, fields

engine = create_engine('sqlite:///test5.db', echo=False)
Session = sessionmaker(bind=engine)
session = Session()

Base = declarative_base()

class Author(Base):
    __tablename__ = 'authors'
    id = Column(Integer, primary_key=True)
    name = Column(String(255))

class Book(Base):
    __tablename__ = 'books'
    id = Column(Integer, primary_key=True)
    title = Column(String(255))
    author_id = Column(Integer, ForeignKey("authors.id"))
    author = relationship("Author", backref="books")

Base.metadata.create_all(engine)

class AuthorSchema(SQLAlchemyAutoSchema):
    class Meta:
        model = Author
        load_instance = True
        include_relationships = True

class BookSchema(SQLAlchemyAutoSchema):
    class Meta:
        model = Book
        load_instance = True
        include_relationships = True

class BookSchemaWithNested(SQLAlchemyAutoSchema):
    class Meta:
        model = Book
        load_instance = True
        include_relationships = True

    author = fields.Nested(AuthorSchema)

author = Author(name="Chuck Paluhniuk")
book = Book(title="Fight Club", author=author)
session.add(author)
session.add(book)
session.commit()

print(AuthorSchema().dump(author)) # {'books': [1], 'name': 'Chuck Paluhniuk', 'id': 1}
print(BookSchema().dump(book)) # {'id': 1, 'title': 'Fight Club', 'author': 1}
print(BookSchemaWithNested().dump(book)) # {'id': 1, 'title': 'Fight Club', 'author': {'books': [1], 'name': 'Chuck Paluhniuk', 'id': 1}}

book = session.query(Book).options(joinedload("author")).get(1)
print(BookSchema().dump(book)) # {'id': 1, 'title': 'Fight Club', 'author': 1}

print(BookSchema._declared_fields["author"]) # <fields.Related(default=<marshmallow.missing>, ...
print(BookSchemaWithNested._declared_fields["author"]) # <fields.Nested(default=<marshmallow.missing>, ...

[rchukkayapally]

mato2000 How did you solve this problem?

[mato2000]

Thanks for the reply! I was trying this example but it was slightly different and didn’t work. Fixed and now works. Thanks and sorry for bothering!