Update Documents¶

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This page uses the following mongo shell methods:

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

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.

Note

Starting in MongoDB 4.2, MongoDB can accept an aggregation pipeline to specify the modifications to make instead of an update document. See the method reference page for details.

Update a Single Document¶

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.

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.

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.

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.

Write Acknowledgement¶

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

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