TypeError: Object of type is not JSON serializable

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

4 Answers

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.

In order to use jsonify() you have to make serializable the class you need to jsonify. Add to that class a function similar to the following:

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')) def serialize(self): return {"id": self.id, "file": self.file, "application_id": self.application_id} 

And then jsonify de serializaed version of the object, and not the objetc itself:

jsonify(result.serialize()) 

This method work for me

class User(db.Model, Timestamp): id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String(20), nullable= False) email = db.Column(db.String(40), unique = True, nullable= False) def toDict(self): return dict(id=self.id, name=self.id email=self.email) 

and

return jsonify([s.toDict() for s in admins]) 

Try with json.dumps() and json.loads()