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db.collection.findAndModify()

Definition

db.collection.findAndModify(document)

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.

The findAndModify() method has the following form:

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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 embedded document fields:

Parameter	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.

Return Data

For remove operations, if the query matches a document, findAndModify() returns the removed document. If the query does not match a document to remove, findAndModify() returns null.

For update operations, findAndModify() returns one of the following:

• If the new parameter is not set or is false:
  • the pre-modification document if the query matches a document;
  • otherwise, null.
• If new is true:
  • the modified document if the query returns a match;
  • the inserted document if upsert: true and no document matches the query;
  • otherwise, null.

Changed in version 3.0: In previous versions, if for the update, sort is specified, and upsert: true, and the new option is not set or new: false, db.collection.findAndModify() returns an empty document {} instead of null.

Behavior

Upsert and Unique Index

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.

In the following example, no document with the name Andy exists, and multiple clients issue the following command:

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

Then, if these clients’ findAndModify() 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, 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, the multiple methods will exhibit one of the following behaviors:

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

Sharded Collections

When using findAndModify in a sharded environment, the query must contain the shard key for all operations against the shard cluster for the sharded collections.

findAndModify operations issued against mongos instances for non-sharded collections function normally.

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 the pre-modified version of the document. 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 method updates and returns an existing document in the people collection where the document matches the query criteria:

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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:

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   {
     "_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.

Upsert

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

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

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

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{ }

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

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null

Return New Document

The following method includes both the upsert: true option and the new:true option. The method 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.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:

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

Sort and Remove

By including a sort specification on the rating field, the following example removes from the people collection a single document with the state value of active and the lowest rating among the matching documents:

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db.people.findAndModify(
   {
     query: { state: "active" },
     sort: { rating: 1 },
     remove: true
   }
)

The method returns the deleted document:

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{
   "_id" : ObjectId("52fba867ab5fdca1299674ad"),
   "name" : "XYZ123",
   "score" : 1,
   "state" : "active",
   "rating" : 3
}

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