Creating schemas to validate, serialize, and deserialize users

Now we will create the Flask-Marshmallow schema that we will use to validate, serialize, and deserialize the previously declared User model. Open the models.py file within the service folder and add the following code after the existing lines. The code file for the sample is included in the restful_python_2_03_02 folder, in the Flask01/service/models.py file:

class UserSchema(ma.Schema): 
    id = fields.Integer(dump_only=True) 
    name = fields.String(required=True,  
        validate=validate.Length(3)) 
    url = ma.URLFor('service.userresource',  
        id='<id>',  
        _external=True) 

The code declares the UserSchema schema, specifically a subclass of the ma.Schema class. Remember that the previous code we wrote for the service/models.py file created a flask_marshmallow.Mashmallow...