Update Operators

The following operators are available for use in update operations such as db.collection.updateMany() and db.collection.findAndModify().

Syntax

Specify update operators in the following form:

{
   <operator1>: { <field1>: <value1>, ... },
   <operator2>: { <field2>: <value2>, ... },
   ...
}

Behavior

Update operators process document fields with string-based names in lexicographic order. Fields with numeric names are processed in numeric order.

Consider this example $set command:

{ $set: { "a.2": <new value>, "a.10": <new value>, } }

"a.2" is processed before "a.10" because 2 comes before 10 in numeric order.

Array Update Modifiers

The following modifiers change how the $push and $addToSet operators update arrays:

Name	Description
`$each`	Modifies the `$push` and `$addToSet` operators to append multiple items for array updates.
`$position`	Modifies the `$push` operator to specify the position in the array to add elements.
`$slice`	Modifies the `$push` operator to limit the size of updated arrays.
`$sort`	Modifies the `$push` operator to reorder documents stored in an array.

Array Update Operators

The following operators modify the contents of an array:

Name	Description
`$addToSet`	Adds elements to an array only if they do not already exist in the set.
`$pop`	Removes the first or last item of an array.
`$pull`	Removes all array elements that match a specified query.
`$pullAll`	Removes all matching values from an array.
`$push`	Adds an item to an array.

Bitwise Update Operators

The following operator performs a bitwise update of an integer value:

Name	Description
`$bit`	Performs bitwise `AND`, `OR`, and `XOR` updates of integer values.

Field Update Operators

The following operators modify fields in a document:

Name	Description
`$currentDate`	Sets the value of a field to current date, either as a Date or a Timestamp.
`$inc`	Increments the value of the field by the specified amount.
`$min`	Only updates the field if the specified value is less than the existing field value.
`$max`	Only updates the field if the specified value is greater than the existing field value.
`$mul`	Multiplies the value of the field by the specified amount.
`$rename`	Renames a field.
`$set`	Sets the value of a field in a document.
`$setOnInsert`	Sets the value of a field if an update results in an insert of a document. Has no effect on update operations that modify existing documents.
`$unset`	Removes the specified field from a document.

Positional Update Operators

The following operators act as placeholders to identify which array elements to update:

Name	Description
`$`	Acts as a placeholder to update the first element that matches the query condition.
`$[]`	Acts as a placeholder to update all elements in an array for the documents that match the query condition.
`$[<identifier>]`	Acts as a placeholder to update all elements that match the `arrayFilters` condition for the documents that match the query condition.

Updates with Aggregation Pipeline

To create expressive update statements, such as conditional updates based on current field values or single-field updates that use the value of another field, you can perform updates with an aggregation pipeline.

For syntax and examples, see Updates with Aggregation Pipeline.

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