How to serialize SqlAlchemy result to JSON?

Question

Django has some good automatic serialization of ORM models returned from DB to JSON format.

How to serialize SQLAlchemy query result to JSON format?

I tried

Answer 1

I recommend using marshmallow. It allows you to create serializers to represent your model instances with support to relations and nested objects.

Here is a truncated example from their docs. Take the ORM model, Author:

class Author(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    first = db.Column(db.String(80))
    last = db.Column(db.String(80))

A marshmallow schema for that class is constructed like this:

class AuthorSchema(Schema):
    id = fields.Int(dump_only=True)
    first = fields.Str()
    last = fields.Str()
    formatted_name = fields.Method("format_name", dump_only=True)

    def format_name(self, author):
        return "{}, {}".format(author.last, author.first)

...and used like this:

author_schema = AuthorSchema()
author_schema.dump(Author.query.first())

...would produce an output like this:

{
        "first": "Tim",
        "formatted_name": "Peters, Tim",
        "id": 1,
        "last": "Peters"
}

Have a look at their full Flask-SQLAlchemy Example.

A library called marshmallow-sqlalchemy specifically integrates SQLAlchemy and marshmallow. In that library, the schema for the Author model described above looks like this:

class AuthorSchema(ModelSchema):
    class Meta:
        model = Author

The integration allows the field types to be inferred from the SQLAlchemy Column types.

marshmallow-sqlalchemy here.