MongoDB list documents not in another list

Question

I have a document with many objects, and several aggregate processors that run on them. Lets say the name of the objects document is Objects. For one processor, I created another document called ProcessedObjects in which each instance is an object that contains one field "processedObjectPtr" which is a link to an object.

I would like to run the following basic loop :

for all objects that haven't been processed yet: 
    1 - process object
    2 - add object to processed object list

The part which I don't know how to do in MongoDB is to get the list of objects that haven't been processed yet. Theoretically I could mark the object itself as processed by adding another field to it, but when I will have many processors that will get ugly, which is why I prefer to keep the 'processed object list' in a separate document.

Is there an elegant way to do this, or will I have to add the processed metadata to the actual objects? I am using mongoengine, but any answer will do.

Thanks!

Answer 1

I ended up adding a 'processedFlags' list to my objects, so each processor could mark (via a flag) that it already processed this object, and also query which objects do not have the flag.