MongoDB Documentation, Release 3.0.4 The update operation returns a WriteResult object which contains the status of the operation, including whether the db.collection.update() method modified an existing document or added a new document. The nMatched field shows that the operation matched 0 documents. The nUpserted of 1 shows that the update added a document. The nModified of 0 specifies that no existing documents were updated. The _id field shows the generated _id field for the added document. For more examples, see Update examples in the db.collection.update() reference page. The db.collection.findAndModify() and the db.collection.save() method can also modify exist- ing documents or insert a new one. See the individual reference pages for the methods for more information and examples. In MongoDB, the db.collection.remove() method removes documents from a collection. You can remove all documents from a collection, remove all documents that match a condition, or limit the operation to remove just a single document. This tutorial provides examples of remove operations using the db.collection.remove() method in the mongo shell. To remove all documents from a collection, pass an empty query document {} to the remove() method. The remove() method does not remove the indexes. The following example removes all documents from the inventory collection: db.inventory.remove({}) To remove all documents from a collection, it may be more efficient to use the drop() method to drop the entire collection, including the indexes, and then recreate the collection and rebuild the indexes. To remove the documents that match a deletion criteria, call the remove() method with the <query> parameter. The following example removes all documents from the inventory collection where the type field equals food : db.inventory.remove( { type : "food" } ) For large deletion operations, it may be more efficient to copy the documents that you want to keep to a new collection and then use drop() on the original collection. Chapter 3. MongoDB CRUD Operations 106 Remove Documents that Match a Condition Remove All Documents 3.3.4 Remove Documents Additional Examples and Methods WriteResult({ "nMatched" : 0, "nUpserted" : 1, "nModified" : 0, "_id" : ObjectId("53dbd7c8babeaec6342ed6c8") })