findAndModify

The findAndModify command 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 command has the following syntax:

{
  findAndModify: <string>,
  query: <document>,
  sort: <document>,
  remove: <boolean>,
  update: <document>,
  new: <boolean>,
  fields: <document>,
  upsert: <boolean>
}

The findAndModify command takes the following fields:

The findAndModify command returns a document, similar to the following:

{
   lastErrorObject: {
                        updatedExisting: <boolean>,
                        upserted: <boolean>,
                        n: <num>,
                        connectionId: <num>,
                        err: <string>,
                        ok: <num>
   }
   value: <document>,
   ok: <num>
}

The return document contains the following fields:

• The lastErrorObject field that returns the details of the command:
  • The updatedExisting field only appears if the command is either an update or an upsert.
  • The upserted field only appears if the command is an upsert.
• The value field that returns either:
  • the original (i.e. pre-modification) document if new is false, or
  • the modified or inserted document if new: true.
• The ok field that returns the status of the command.

Consider the following examples:

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

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

  This command 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 command 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 command returns a document with the following fields:

     • The lastErrorObject field that contains the details of the command, including the field updatedExisting which is true, and
     • The value field that contains the original (i.e. pre-modification) document selected for this update:

     {
       "lastErrorObject" : {
          "updatedExisting" : true,
          "n" : 1,
          "connectionId" : 1,
          "err" : null,
          "ok" : 1
       },
       "value" : {
          "_id" : ObjectId("50f1d54e9beb36a0f45c6452"),
          "name" : "Tom",
          "state" : "active",
          "rating" : 100,
          "score" : 5
       },
       "ok" : 1
     }
     

     To return the modified document in the value field, add the new:true option to the command.

     If no document match the query condition, the command returns a document that contains null in the value field:

     { "value" : null, "ok" : 1 }
     

  The mongo shell and many drivers provide a findAndModify() helper method. Using the shell helper, this previous operation can take the following form:

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

  However, the findAndModify() shell helper method returns just the unmodified document, or the modified document when new is true.

  {
     "_id" : ObjectId("50f1d54e9beb36a0f45c6452"),
     "name" : "Tom",
     "state" : "active",
     "rating" : 100,
     "score" : 5
  }
  

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

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

  If the command does not find a matching document, the command performs an upsert and returns a document with the following fields:

  • The lastErrorObject field that contains the details of the command, including the field upserted that contains the ObjectId of the newly inserted document, and
  • The value field that contains an empty document {} as the original document because the command included the sort option:

  {
    "lastErrorObject" : {
       "updatedExisting" : false,
       "upserted" : ObjectId("50f2329d0092b46dae1dc98e"),
       "n" : 1,
       "connectionId" : 1,
       "err" : null,
       "ok" : 1
    },
    "value" : {
  
    },
    "ok" : 1
  }
  

  If the command did not include the sort option, the value field would contain null:

  {
    "value" : null,
    "lastErrorObject" : {
       "updatedExisting" : false,
       "n" : 1,
       "upserted" : ObjectId("5102f7540cb5c8be998c2e99")
    },
    "ok" : 1
  }
  

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

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

  The command returns the newly inserted document in the value field:

  {
    "lastErrorObject" : {
       "updatedExisting" : false,
       "upserted" : ObjectId("50f47909444c11ac2448a5ce"),
       "n" : 1,
       "connectionId" : 1,
       "err" : null,
       "ok" : 1
    },
    "value" : {
       "_id" : ObjectId("50f47909444c11ac2448a5ce"),
       "name" : "Pascal",
       "rating" : 25,
       "score" : 1,
       "state" : "active"
    },
    "ok" : 1
  }
  

When the findAndModify command 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 issue the findAndModify command and these commands complete the find phase before any one starts the modify phase, these commands could insert the same document.

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

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

If all the commands 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, then the multiple findAndModify commands would observe one of the following behaviors:

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