Query on results of query in MongoDB

Question

I have a mongo database and several collections in it. I want to remove from collections all entiries that match, say, target_id. The trick is that I also have to remove entries "connected" to entries that match target_id.

For example

DB
Culture   (_id, owner_id)
Document  (_id, target_id)
Entity    (_id, target_id)
Field     (_id, entity_id)
Form      (_id, target_id)
Question  (_id, form_id)
Layout    (_id, question_id)

Now, I can easilily remove all documents by

db.Document.remove( {"_id": ObjectId(target_id)});

So the first tricky part, is that some entry in Culture collection may have owner_id = document_id. So before I remove entity entry I have to also remove culture entry.

Second problem is that I can't directly access by target_id entries in field collection, because those fields can be found by entity_id.

So I'd like to write a script/query to run from mongo shell providing target_id and then remove all entries directly or indirectly "referenced" by target_id. I haven't had experience beyong simple find/delete by id, so this query got be stuck.

As far as I understand I can do this step by step, say, first find all entities:

db.Entity.find({ "$where" : "{"target_id" : ObjectId(target_id)}" });

The second step is to remove all cultures that have owner_id = entity id of every entity from query above. How can I run

db.Culture.find({ "$where" : "{"owner_id" : ObjectId(entity_id)}" });

Where entity_id iterate over all enties the the first query?

seems your data is relational... mongo is not a good alternative for this kind of stuff. — tanaydin
– tanaydin, Commented Apr 10, 2013 at 13:14

Hertzel Guinness · Accepted Answer · 2013-04-10 11:25:54Z

1

IIUC, you are looking for the $in operator.

set1 = Find all ids you want to delete
set2 = Find all referenced ids of ids in set1
Remove all documents matching that ids with the in operator with set2
Remove all documents matching that ids with the in operator with set1

Do this repeatedly down the hierarchy...

Example:

db.Culture.find({"owner_id" : {"$in":[set_of_entityids]" }});

Note you get bson ids from queries, so you probably don't need to prefix with ObjectId

HTH

edited Apr 10, 2013 at 11:25

answered Apr 10, 2013 at 11:20

Hertzel Guinness

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2 Comments

Sammaye Over a year ago

What is IIUC? Is it some kind of slang

Hertzel Guinness Over a year ago

If I Understand Correctly :)

Devesh · Accepted Answer · 2013-04-10 11:22:39Z

0

One of the way of doing it using findAndMondify . You can update the document at the same time you will also get the Ids back . So you will mark the documents as ACTIVE = FALSE , and then get the Ids back in findAndModify . In the last just remove all the entries which is ACTIVE = FALSE. You can see how I have used in my application : http://devesh4blog.wordpress.com/2013/03/01/findandmodify-in-mongodb-a-practical-example/

answered Apr 10, 2013 at 11:22

Devesh

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