Why is post_load called after schema.validate()?

Hello,

I noticed that @post_load is called when calling schema_object.validate().

Then I went to the library code and saw this (everything seemed OK, because I was getting a feeling postprocessing will not take a place):

It was obvious I will need some debugging, so I went through the calling stacktrace and got surprised when I saw the marshalling module calls the deserialize method which calls schema_object.load(). I don’t think it is expected to have post_load called when you call schema_object.validate(), because in my case, we are performing some intensive operations, e.g. b64 decoding some string data and it takes some time. In this way, we have post_load called twice - the first time when a controller validates the input and the other when we actually load the data into a dict.

Of course, this is not a bug, but an open question.

[deckar01]

I was able to repro on 3.2.0. Here is a minimal repro case:

from marshmallow import Schema, fields, post_load

class Foo(Schema):
    bar = fields.Str()
    
    @post_load
    def test_post_load(self, data, **kwargs):
        assert False

class Test(Schema):
    foo = fields.Nested(Foo)

Test().validate({'foo': {'bar': 'test'}})
# AssertionError

This is an artifact of validation calling _do_load under the hood. Propagating postprocess through the field load calls would work, but this might be a good opportunity to consider separating validation from loading. There has been recurring interest in validating objects that have already been deserialized.

[deckar01]

I don’t think it is expected to have post_load called when you call schema_object.validate()

from marshmallow import Schema, fields, post_load

class Test(Schema):
    foo = fields.Str()
    
    @post_load
    def test_post_load(self, data):
        assert False

Test().validate({'foo': 'test'})
# {}

It doesn’t seem to be called in marshmallow 2 or 3.

Of course, this is not a bug, but an open question.

If post_load was being called during validate it would be a bug. I can’t reproduce that behavior.