findAndModify¶

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Definition
Output
Behavior
Examples

Definition¶

findAndModify¶

The findAndModify command 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:

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

The findAndModify command takes the following fields:

Field	Type	Description
`query`	document	Optional. The selection criteria for the modification. The `query` field employs the same query selectors as used in the `db.collection.find()` method. Although the query may match multiple documents, `findAndModify` will only select one document to modify.
`sort`	document	Optional. Determines which document the operation modifies if the query selects multiple documents. `findAndModify` modifies the first document in the sort order specified by this argument.
`remove`	Boolean	Must specify either the `remove` or the `update` field. Removes the document specified in the `query` field. Set this to `true` to remove the selected document . The default is `false`.
`update`	document	Must specify either the `remove` or the `update` field. Performs an update of the selected document. The `update` field employs the same update operators or `field: value` specifications to modify the selected document.
`new`	Boolean	Optional. When `true`, returns the modified document rather than the original. The `findAndModify` method ignores the `new` option for `remove` operations. The default is `false`.
`fields`	document	Optional. A subset of fields to return. The `fields` document specifies an inclusion of a field with `1`, as in: `fields: { <field1>: 1, <field2>: 1, ... }`. See projection.
`upsert`	Boolean	Optional. Used in conjunction with the `update` field. When `true`, `findAndModify` creates a new document if no document matches the `query`, or if documents match the `query`, `findAndModify` performs an update. To avoid multiple upserts, ensure that the `query` fields are uniquely indexed. The default is `false`.
`findAndModify`	string	The collection against which to run the command.

Output¶

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 specifies an update or an update with upsert: true; i.e. the field does not appear for a remove.
- The upserted field only appears if the update with the upsert: true operation results in an insertion.
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.

Note

If the findAndModify finds no matching document, then:

for update or remove operations, lastErrorObject does not appear in the return document and the value field holds a null.
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```
{ "value" : null, "ok" : 1 }
```
for update with upsert: true operation that results in an insertion, if the command also specifies new is false and specifies a sort, the return document has a lastErrorObject, value, and ok fields, but the value field holds an empty document {}.
for update with upsert: true operation that results in an insertion, if the command also specifies new is false but does not specify a sort, the return document has a lastErrorObject, value, and ok fields, but the value field holds a null.

Behavior¶

Upsert and Unique Index¶

When the findAndModify command includes the upsert: true option and the query field(s) is not uniquely indexed, the command could insert a document multiple times in certain circumstances.

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

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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 each perform an upsert, creating multiple duplicate documents.

To prevent the creation of multiple duplicate documents, create a unique index on the name field. With the unique index in place, then the multiple findAndModify commands will exhibit one of the following behaviors:

Exactly one findAndModify successfully inserts a new document.
Zero or more findAndModify commands update the newly inserted document.
Zero or more findAndModify commands fail when they attempt 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.

Sharded Collections¶

When using findAndModify in a sharded environment, the query must contain the shard key for all operations against the shard cluster. findAndModify operations issued against mongos instances for non-sharded collections function normally.

Concurrency¶

This command obtains a write lock on the affected database and will block other operations until it has completed; however, typically the write lock is short lived and equivalent to other similar update() operations.

Comparisons with the `update` Method¶

When updating a document, findAndModify and the update() method operate differently:

By default, both operations modify a single document. However, the update() method with its multi option can modify more than one document.
If multiple documents match the update criteria, for findAndModify, you can specify a sort to provide some measure of control on which document to update.

With the default behavior of the update() method, you cannot specify which single document to update when multiple documents match.
By default, findAndModify method returns an object that contains the pre-modified version of the document, as well as the status of the operation. To obtain the updated document, use the new option.

The update() method returns a WriteResult object that contains the status of the operation. To return the updated document, use the find() method. However, other updates may have modified the document between your update and the document retrieval. Also, if the update modified only a single document but multiple documents matched, you will need to use additional logic to identify the updated document.
You cannot specify a write concern to findAndModify to override the default write concern whereas, starting in MongoDB 2.6, you can specify a write concern to the update() method.

When modifying a single document, both findAndModify and the update() method atomically update the document. See Atomicity and Transactions for more details about interactions and order of operations of these methods.

Examples¶

Update and Return¶

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

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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:

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

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:

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{
  "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:

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{ "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:

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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 only the unmodified document, or if new is true, the modified document.

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

`upsert: true`¶

The following findAndModify command includes the upsert: true option for the update operation to either update a matching document or, if no matching document exists, create a new document:

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

If the command finds a matching document, the command performs an update.

If the command does not find a matching document, the update with upsert: true operation results in an insertion 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:

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{
  "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:

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

Return New Document¶

The following findAndModify command includes both upsert: true option and the new:true option. The command either updates a matching document and returns the updated document or, if no matching document exists, inserts a document and returns the newly inserted document in the value field.

In the following example, no document in the people collection matches the query condition:

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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:

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{
  "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
}

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findAndModify¶

Definition¶

Output¶

Behavior¶

Upsert and Unique Index¶

Sharded Collections¶

Concurrency¶

Comparisons with the update Method¶

Examples¶

Update and Return¶

upsert: true¶

Return New Document¶

Comparisons with the `update` Method¶

`upsert: true`¶