Mongoengine: How to increment a attribute inside a EmbeddedDocument in a EmbeddedDocumentListField

[BJKPriyanka]

class Related(EmbeddedDocument):
    type = StringField()
   volume = IntField()

class Main(Document):
   name = StringField()
   relatives = EmbeddedDocumentListField(Related)

I have a object for Main which has relatives. How can i increment the volume parameter of Related EmbeddedDocument from the Main object.

[JohnAD]

If I understand your question correctly:

doc = Main.objects.first()
doc.relatives.volume[0] += 1

The above assumes you have at least one item in relatives. To update any/all of them:

doc = Main.objects.first()
for r in doc.relatives:
    r.volume += 1

Just FYI, your original is title is more correct. volume is an _instance attribute_ of Related.

[JohnAD]

Also, if some volume attributes are missing or None, then you might do:

    if r.volume
        r.volume += 1
    else:
        r.volume = 1

or to be fancy:

     r.volume = 1 + r.volume or 0

[BJKPriyanka]

Thanks @JohnAD .

If i want to filter the relatives of type "parental" and then increment the volume of the filtered relatives. How can I do that?

I figured out how to filter the relatives based on type

doc.relatives.filter(type='parental')
I am confused how to go further to increment. I tried the following but it didn't help me:

doc.relatives.filter(type='parental').update(inc__volume =1)

[JohnAD]

The documentation for the update method of EmbeddedDocumentListField is very sparse and does not explain explain what **update means other than _"A dictionary of update values to apply to each embedded document."_

It implies that you can use update methods similar to other functions. But it actually only does replacement. So volume=1 works. It will think inc__volume is a field name rather than an instruction.

The only way to do what you want is with a loop.

for r in doc.relatives.filter(type='parental'):
    r.volume += 1

[JohnAD]

I just did a simple pull request to update the API documentation for added clarity.

[bagerard]

I believe this can be closed