Execute code before creating document in mongoengine

Question

How can I execute some code only when a document is created in mongoengine, not when updated.

class Account(Document):
    name = StringField(max_length=80, default=None)
    username = StringField(max_length=60, required=True)
    created_at = DateTimeField(default=datetime.now(), required=True)
    updated_at = DateTimeField(default=datetime.now(), required=True)

    meta = {
        'collection': 'accounts'
    }

Now I want to generate random username and assign it to the username field before a document is created.

Any help is appreciated. Thanks.

Answer 1

You should use one of the MongoEngine's signals - pre_save() sounds like a good fit. There are different ways to attach an event handler to a signal, here is one of them:

from mongoengine import signals

class Account(Document):
    # ...

    @classmethod
    def pre_save(cls, sender, document, **kwargs):
        document.username = "random username"

signals.pre_save.connect(Account.pre_save, sender=Account)