Using MongoDB

Remove Data

Learning Objectives

Remove documents that match a condition, or all documents
Drop a collection
Restore example data from the command line using mongoimport
mongoimport expects one document per line (not a valid JSON file)

You can use the remove() method to remove documents from a collection. The method takes a conditions document that determines the documents to remove. To specify a remove condition, use the same structure and syntax as the query conditions.

Let’s remove the fake material we may have upserted during a recent exercise:

db.materials.remove({material_id: "mp-NaN"})

WriteResult({ "nRemoved" : 1 })

Let’s proceed to destroy our materials collection (dont’ worry – we’ll reload everything at the beginning of the next topic).

First, let’s delete all one-element compounts:

db.materials.remove({"nelements": 1})

WriteResult({ "nRemoved" : 419 })

We’re impatient. Let’s just remove everything by specifying an empty conditions document:

db.materials.remove({})

WriteResult({ "nRemoved" : 65721 })

db.materials.count()

I’m glad we have a backup!

The remove() operation only removes the documents from the collection. The collection itself, as well as any indexes for the collection (we’ll go over indexes later), remain. To remove all documents from a collection, it may be more efficient to drop the entire collection, including the indexes, and then recreate the collection and rebuild the indexes. Use the drop() method to drop a collection, including any indexes.

db.materials.drop()

true

(Re)Importing Your Data

Now, let’s re-import the data to the materials collection on the swc database on the default host and port:

exit

bye

mongoimport mongo-novice-materials.json --db swc --collection materials --jsonArray

connected to: localhost
imported 66140 objects

mongo

MongoDB shell version: 3.2.3
connecting to: test

use swc

switched to db swc