How to remove a item from a list(ListField) by id

Question

structure：

{title: 'test', comments: [{id:1, title: ''}, {id: 8, title: ''}]}

i need remove the id=8 item, thanks.

Answer 1

Here is one example of the pull operator, using flask_mongoengine and assuming the parent object class is called Blog, and the comments are EmbeddedDocuments within Blog.

Blog.objects(id=blog_id).update_one(pull__comments___id=comment_id)

Notice the triple underscore in comments id. This is because if you want primary keys on Comments, you need to add one in your model declaration like this:

class Comment(db.EmbeddedDocument):
    _id = db.ObjectIdField(primary_key=True, default=lambda: ObjectId())
    ...

The lamba function will generate your primary keys for you.

Answer 2

Hi you can pull items from an array:

https://github.com/hmarr/mongoengine/blob/master/tests/queryset.py#L1374

See $pull: http://www.mongodb.org/display/DOCS/Updating#Updating-%24pull

Answer 3

You need to use $pull operator here :

http://www.mongodb.org/display/DOCS/Updating#Updating-%24pull

db.collection.update({'title':'test'},{$pull : { 'comments' : { 'id' : 8 }});