Question

There are a few posts here about this but not exactly what I’m after.

I have a document that contains a list of embedded documents:

{
   "_id": 1234
   "name": "joe"
   "comments": [
       {"type": "text", "content": "my content"},
       {"type": "image", "content": "my_content"}
       {"type": "image", "content": "my_content"}
   ]

}

I want to run one query that gets a set of documents then I was hoping to run a secondary query to search the “comments” list from that initial query set.

e.g p = db.people.find({"some":"condition"}) and then search the embedded docs like p.find({"type":"image"}

This obviously doesn’t work. Just wondering if there’s a way to do this without having to run 2 separate queries over the parent document collection again?

Answer 1

If you want to just find the items in a collection that satisfy a given condition and also satisfy {"type": "image"} in the comments array, you can do that in a single query:

p = db.people.find({"some": "condition", "comments.type": "image"})

See the dot notation page for more info.

If you do actually need the whole thing, and you’re interested in specific sub-items from said result, then the best method that I can think of is just to slurp in the result into a list, and check it in Python. Do any PyMongo gurus have anything to say on this? Note that, if your dataset is large, then this is not a good idea.

p = list(db.people.find({"some": "condition"})

# A little verbose, but...
image_p = [item for item in p
           if any(comment['type'] == 'image'
                  for comment in item['comments'])]

...