Dump Validation

Hi everyone !!

I having some troubles with dump. I want the lib raise a error when some variables in object is missing.

I made the test bellow to explain and the assert failed because nothing is raised.

Is it a bug of dump?

` from marshmallow import Schema, fields

def test_dump():

class TesteClass:
    def __init__(self):
        self.variable_a = 1

class TesteSchemaClass(Schema):
    variable_a = fields.Integer(required=True)
    variable_b = fields.Integer(required=True)

teste = TesteClass()

schema = TesteSchemaClass()

data, error = schema.dump(teste)

assert len(error.keys()) == 1

`

[deckar01]

The correct way to do this is to dump the data, then load it. If the data types are wrong you will probably get errors during dump. This is how it always worked, you just get the real errors instead of ValidationErrors now. If the values are wrong, you will get ValidationErrors during the load operation.

[deckar01]

Schema.dump() also returns a dictionary of errors, which will include any ValidationErrors raised during serialization. However, required, allow_none, validate, @validates, and @validates_schema only apply during deserialization.

https://marshmallow.readthedocs.io/en/3.0/quickstart.html#validation

Not being able to trust the structure of the object is usually a sign that it is actually data that needs to be loaded. You can use schema.validate(data), but under the hood it is doing the same thing as schema.load(data), it just returns the errors instead of raising them.

https://marshmallow.readthedocs.io/en/3.0/api_reference.html#marshmallow.Schema.validate