Embedded Documents issue with MongoEngine

Question

I am using MongoDB with Flask-MongoEngine as my ORM component to my web app.

I have structured the User document schema like so:

from ..core import db

class UserComics(db.EmbeddedDocument):
    favorites = db.SortedListField(db.StringField(), default=None)

class UserSettings(db.EmbeddedDocument):
    display_favs = db.BooleanField(default=False)
    default_cal = db.StringField(default=None)
    show_publishers = db.ListField(db.StringField(), default=None)

class UserTokens(db.EmbeddedDocument):
    refresh_token = db.StringField(default=None)
    access_token = db.StringField(default=None)
    expire_time = db.StringField(default=None)

class User(db.Document, UserMixin):
    # Save User document to this collection
    meta = {'collection': 'users_test'}

    userid = db.StringField()
    full_name = db.StringField()
    first_name = db.StringField()
    last_name = db.StringField()
    gender = db.StringField()
    birthday = db.StringField()
    email = db.EmailField()
    friends = db.ListField(db.StringField())
    date_creation = db.DateTimeField()
    last_login = db.DateTimeField()
    favorites = db.EmbeddedDocumentField(UserComics)
    settings = db.EmbeddedDocumentField(UserSettings)
    tokens = db.EmbeddedDocumentField(UserTokens)

However, When creating a new user like this (I have left out lines...):

def create_new_user(resp):
    newUser = User()
    ....
    newUser.settings.default_cal = resp['calendar']
    ....
    newUser.save()
    return

I run into this error:

AttributeError: 'NoneType' object has no attribute 'default_cal'

It seems to me that I am not using MongoEngines Embedded documents correctly but I do not know where I am going wrong.

Any help would be greatly appreciated!

Twocycle

Answer 1

Well you just have to create an embedded document object of the particular class, and then use it with the main document class, like so:

new_user = User()
user_settings = UserSettings()
user_settings.default_cal = resp['calendar']
new_user.settings = user_settings
# more stuff
new_user.save()

Note: Creating a new object only for the main document, does not automatically create the corresponding embedded document object(s), but while reading data ofcourse the case is different.

Edit:

As tbicr mentions below, we can also do this:

settings = db.EmbeddedDocumentField(UserSettings, default=UserSettings)

while declaring the field, that way we won't need to create the object as given in the first example.

Asshur

Or create embedded document by default: db.EmbeddedDocumentField(UserSettings, default=UserSettings). – Israelite

Thank you! This is exactly what I needed to know. Everything is working as expected now! – Twocycle