TypeError: Object of type is not JSON serializable

Question

I'm wrote rest on the Flask using flask-marshmallow

models.py

class Application(db.Model):
    __tablename__ = 'applications'

    id = db.Column(db.String(), primary_key=True)
    name = db.Column(db.String())
    versions = db.relationship('Version', backref='application', lazy=True)

    def __repr__(self):
        return '<application {}>'.format(self.name)


class Version(db.Model):
    __tablename__ = 'versions'

    id = db.Column(db.String(), primary_key=True)
    file = db.Column(db.String(80), nullable=True)
    application_id = db.Column(db.Integer, db.ForeignKey('applications.id'))

shemas.py

class ApplicationDetailSchema(ma.Schema):
    class Meta:
        fields = ('id', 'name', 'versions')

routes.py

@bp.route("/<id>")
def application_detail(id):
    application = Application.query.get(id)
    result = application_detail_schema.dump(application)
    return jsonify(result)

TypeError: Object of type 'Version' is not JSON serializable

Answer 1

You probably want to use ModelSchema instead of Schema.

class ApplicationDetailSchema(ma.ModelSchema):
    class Meta:
        model = Application
        fields = ('id', 'name', 'versions')

ModelSchema dumps the related foreign key objects as a list of id(s) by default which is JSON serializable.