What is the proper way to update a listfield of embedded documents in mongoengine?

Question

I am trying to define methods for performing checks and updates to a listfield of embedded documents in mongoengine. What is the proper way of doing what I'm trying to do. The code is below.

class Comment(EmbeddedDocument):
    created = DateTimeField()
    text = StringField()

class Post(Document):
    comments = ListField(EmbeddedDocumentField(Comment))

    def check_comment(self, comment):
        for existing_comment in self.comments:
            if comment.created == existing_comment.created and 
                comment.text == existing_comment.text:
                return True
        return False

    def add_or_replace_comment(self, comment):
        for existing_comment in self.comments:
            if comment.created == existing_comment.created:
                # how do I replace?

        # how do I add?

Is this even the correct way to go about something like this?

Answer 1

You could use an EmbeddedDocumentListField instead of a list of embedded documents. That way you get access to some handy methods like filter, create or update:

class Comment(EmbeddedDocument):
    created = DateTimeField()
    text = StringField()

class Post(Document):
    comments = EmbeddedDocumentListField(Comment)

    ...

    def add_or_replace_comment(self, comment):
        existing = self.comments.filter(created=comment.created)
        if existing.count() == 0:
             self.comments.create(comment)
        else:
             existing.update(comment)

(code not tested)

Answer 2

You need to find the index of the existing comment.

You can then overwrite the old comment with the new comment (where i is the index) eg:

post.comments[i] = new_comment

then just do a post.save() and mongoengine will convert that to a $set operation.

Alternatively, you could just write the $set eg:

Post.objects(pk=post.pk).update(set__comments__i=comment)