Update Documents¶

This page provides examples of how to update documents in MongoDB. The examples use the following methods in the mongo shell:

db.collection.updateOne(<filter>, <update>, <options>)
db.collection.updateMany(<filter>, <update>, <options>)
db.collection.replaceOne(<filter>, <replacement>, <options>)

The examples on this page use the inventory collection. To create and/or populate the inventory collection, run the following in the mongo shell:

db.inventory.insertMany( [
   { item: "canvas", qty: 100, size: { h: 28, w: 35.5, uom: "cm" }, status: "A" },
   { item: "journal", qty: 25, size: { h: 14, w: 21, uom: "cm" }, status: "A" },
   { item: "mat", qty: 85, size: { h: 27.9, w: 35.5, uom: "cm" }, status: "A" },
   { item: "mousepad", qty: 25, size: { h: 19, w: 22.85, uom: "cm" }, status: "P" },
   { item: "notebook", qty: 50, size: { h: 8.5, w: 11, uom: "in" }, status: "P" },
   { item: "paper", qty: 100, size: { h: 8.5, w: 11, uom: "in" }, status: "D" },
   { item: "planner", qty: 75, size: { h: 22.85, w: 30, uom: "cm" }, status: "D" },
   { item: "postcard", qty: 45, size: { h: 10, w: 15.25, uom: "cm" }, status: "A" },
   { item: "sketchbook", qty: 80, size: { h: 14, w: 21, uom: "cm" }, status: "A" },
   { item: "sketch pad", qty: 95, size: { h: 22.85, w: 30.5, uom: "cm" }, status: "A" }
]);

You can run the operation in the web shell below:

Update Documents in a Collection¶

To update a document, MongoDB provides update operators, such as $set, to modify field values. To use the update operators, pass to the update methods an update document of the form:

{
  <update operator>: { <field1>: <value1>, ... },
  <update operator>: { <field2>: <value2>, ... },
  ...
}

Some update operators, such as $set, will create the field if the field does not exist. See the individual update operator reference for details.

Update Documents via `db.collection.updateOne()`¶

The following example uses the db.collection.updateOne() method on the inventory collection to update the first document where item equals "paper".

db.inventory.updateOne(
   { item: "paper" },
   {
     $set: { "size.uom": "cm", status: "P" },
     $currentDate: { lastModified: true }
   }
)

The update operation:

uses the $set operator to update the value of the size.uom field to "cm" and the value of the status field to "P",
uses the $currentDate operator to update the value of the lastModified field to the current date. If lastModified field does not exist, $currentDate will create the field. See $currentDate for details.

For more information and examples, see db.collection.updateOne().

Update Documents via `db.collection.updateMany()`¶

New in version 3.2.

The following example uses the db.collection.updateMany() method on the inventory collection to update all documents where qty is less than 50.

db.inventory.updateMany(
   { "qty": { $lt: 50 } },
   {
     $set: { "size.uom": "in", status: "P" },
     $currentDate: { lastModified: true }
   }
)

The update operation:

uses the $set operator to update the value of the size.uom field to "in" and the value of the status field to "P",
uses the $currentDate operator to update the value of the lastModified field to the current date. If lastModified field does not exist, $currentDate will create the field. See $currentDate for details.

For more information and examples, see db.collection.updateMany().

Replace the Document¶

To replace the entire content of a document except for the _id field, pass an entirely new document as the second argument to db.collection.replaceOne(). When replacing a document, the replacement document must consist of only <field> : <value> pairs; i.e. do not include update operators expressions.

The replacement document can have different fields from the original document. In the replacement document, you can omit the _id field since the _id field is immutable; however, if you do include the _id field, it must have the same value as the current value.

Replace a Document via `db.collection.replaceOne`¶

The following example uses the db.collection.replaceOne() method on the inventory collection to replace the first document matches the filter item equals "paper":

db.inventory.replaceOne(
   { item: "paper" },
   { item: "paper", instock: [ { warehouse: "A", qty: 60 }, { warehouse: "B", qty: 40 } ] }
)

Behavior¶

Atomicity¶

All write operations in MongoDB are atomic on the level of a single document. For more information on MongoDB and atomicity, see Atomicity and Transactions.

`_id` Field¶

Once set, you cannot update the value of the _id field nor can you replace an existing document with a replacement document that has a different _id field value.

Document Size¶

When performing update operations that increase the document size beyond the allocated space for that document, the update operation relocates the document on disk.

Field Order¶

MongoDB preserves the order of the document fields following write operations except for the following cases:

The _id field is always the first field in the document.
Updates that include renaming of field names may result in the reordering of fields in the document.

Changed in version 2.6: Starting in version 2.6, MongoDB actively attempts to preserve the field order in a document. Before version 2.6, MongoDB did not actively preserve the order of the fields in a document.

`Upsert` Option¶

If db.collection.updateOne(), db.collection.updateMany(), or db.collection.replaceOne() includes upsert : true and no documents match the specified filter, then the operation creates a new document and inserts it. If there are matching documents, then the operation modifies or replaces the matching document or documents.

For details on the new document created, see the individual reference pages for the methods.

Write Acknowledgement¶

With write concerns, you can specify the level of acknowledgement requested from MongoDB for write operations. For details, see Write Concern.

[1]	You can use the `DBQuery.shellBatchSize` to change the number of iteration from the default value `20`. See Working with the mongo Shell for more information.