Mongoengine: `pull` not working for EmbeddedDocumentListField, only working for ListFields

[kushalmitruka]

Hi,
I am using mongoengine. I have came across a weird issue when I was trying to use pull and push for ListFields and EmbeddedDocumentListFields. I realised it is a issue in mongoengine (according to me). The issue is one cannot do a pull query from a EmbeddedDocumentListField but can do the same in ListField.

I traced down this issue and found in mongoengine.queryset.transform.update() has a different logic to handle pull among UPDATE_OPERATORS in case key has . , Under this condition only ListField are allowed to reform key with . operator due to which a query like - embfield__emb_list_field will result in {'emb_field': {'emb_list_field': whereas it should be {'emb_field.emb_list_field':.

Let me know if this is a bug or I am making some mistake and if its a bug can i submit a patch to fix this

[erdenezul]

Can you provide sample of your code in order to get error and understand your problem fully. If you show the code sample, someone would be able to help.

[kushalmitruka]

Hi, I am glad that you replied. Below is the code snippet which I was using and found this issue.

class Identity(document.EmbeddedDocument):
    class Address(document.EmbeddedDocument):
          pincode = fields.StringField()
          city = fields.StringField()

    registeration_number = fields.StringField()
    address = fields.EmbeddedDocumentListField(fields.EmbeddedDocumentField())

class Company(documents.Document):
    company_ids = fields.EmbeddedDocumentField(Identity)

Now I an performing certain operations where I came across this issue -
comp = Company.objects.first()
add_1 = Identity.Address()
comp.update(push__company_ids__address=add_1) <-- Runs fine
comp.update(pull__company_ids__address=add_1) <-- throws Operation Error

This is the Exact Error which I get -
OperationError: Update failed (Cannot apply $pull to a non-array value)

After running debugger I found that in mongoengine/queryset/base in update funtion. the update dict that gets created is -
{'$pull': {'company_ids': {'address': SON(Address Object)}}

Also for list field of such cases it creates -
{$pull: {'company_ids.address': SON(Address Object)}

In case the address field in Identity class is ListField both Push and Pull runs fine.

[erdenezul]

mongo_update value for push operation
{'company_ids.address': SON([('pincode', u'1234'), ('city', u'UB')])}}
mongo_update value for pull operation
{'$pull': {'company_ids': {'address': SON([('pincode', u'1234'), ('city', u'UB')])}}}

In my opinion, these values are supposed to be same, then it is considered as a bug.
You should send PR, let the contributors decide if it's merge or drop. Otherwise, you will be fine in case that of using ListField :)

[kushalmitruka]

@erdenezul , Raised the PR : https://github.com/MongoEngine/mongoengine/pull/1765

[bagerard]

Looks like PR got merged, can we close this?