db.collection.findAndModify()

The db.collection.findAndModify() method atomically modifies and returns a single document. By default, the returned document does not include the modifications made on the update. To return the document with the modifications made on the update, use the new option. The findAndModify() method is a shell helper around the findAndModify command.

db.collection.findAndModify( {
                               query: <document>,
                               sort: <document>,
                               remove: <boolean>,
                               update: <document>,
                               new: <boolean>,
                               fields: <document>,
                               upsert: <boolean>
                           } );

The db.collection.findAndModify() method takes a document parameter with the following subdocument fields:

The findAndModify() method returns either:

• the pre-modification document or,
• if the new: true option is set, the modified document.

Consider the following examples:

• The following method updates an existing document in the people collection where the document matches the query criteria:

  db.people.findAndModify( {
      query: { name: "Tom", state: "active", rating: { $gt: 10 } },
      sort: { rating: 1 },
      update: { $inc: { score: 1 } }
  } )
  

  This method performs the following actions:

  1. The query finds a document in the people collection where the name field has the value Tom, the state field has the value active and the rating field has a value greater than 10.

  2. The sort orders the results of the query in ascending order. If multiple documents meet the query condition, the method will select for modification the first document as ordered by this sort.

  3. The update increments the value of the score field by 1.

  4. The method returns the original (i.e. pre-modification) document selected for this update:

     {
       "_id" : ObjectId("50f1e2c99beb36a0f45c6453"),
       "name" : "Tom",
       "state" : "active",
       "rating" : 100,
       "score" : 5
     }
     

     To return the modified document, add the new:true option to the method.

     If no document matched the query condition, the method returns null:

     null
     

• The following method includes the upsert: true option to insert a new document if no document matches the query condition:

  db.people.findAndModify( {
      query: { name: "Gus", state: "active", rating: 100 },
      sort: { rating: 1 },
      update: { $inc: { score: 1 } },
      upsert: true
    } )
  

  If the method does not find a matching document, the method performs an upsert. Because the method included the sort option, it returns an empty document { } as the original (pre-modification) document:

  { }
  

  If the method did not include a sort option, the method returns null.

  null
  

• The following method includes both the upsert: true option and the new:true option to return the newly inserted document if a document matching the query is not found:

  db.people.findAndModify( {
      query: { name: "Pascal", state: "active", rating: 25 },
      sort: { rating: 1 },
      update: { $inc: { score: 1 } },
      upsert: true,
      new: true
    }
  )
  

The method returns the newly inserted document:

{
  "_id" : ObjectId("50f49ad6444c11ac2448a5d6"),
  "name" : "Pascal",
  "rating" : 25,
  "score" : 1,
  "state" : "active"
}

When findAndModify() includes the upsert: true option and the query field(s) is not uniquely indexed, the method could insert a document multiple times in certain circumstances. For instance, if multiple clients each invoke the method with the same query condition and these methods complete the find phase before any of methods perform the modify phase, these methods could insert the same document.

Consider an example where no document with the name Andy exists and multiple clients issue the following command:

db.people.findAndModify(
                         {
                           query: { name: "Andy" },
                           sort: { rating: 1 },
                           update: { $inc: { score: 1 } },
                           upsert: true
                         }
                       )

If all the methods finish the query phase before any command starts the modify phase, and there is no unique index on the name field, the commands may all perform an upsert. To prevent this condition, create a unique index on the name field. With the unique index in place, the multiple methods would observe one of the following behaviors:

• Exactly one findAndModify() would successfully insert a new document.
• Zero or more findAndModify() methods would update the newly inserted document.
• Zero or more findAndModify() methods would fail when they attempted to insert a duplicate. If the method fails due to a unique index constraint violation, you can retry the method. Absent a delete of the document, the retry should not fail.