$pop

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Definition

Behavior
Examples

Definition

$pop

The $pop operator removes the first or last element of an array. Pass $pop a value of -1 to remove the first element of an array and 1 to remove the last element in an array.

The $pop operator has the form:

{ $pop: { <field>: <-1 | 1>, ... } }

To specify a <field> in an embedded document or in an array, use dot notation.

Behavior

Starting in MongoDB 5.0, update operators process document fields with string-based names in lexicographic order. Fields with numeric names are processed in numeric order. See Update Operators Behavior for details.

The $pop operation fails if the <field> is not an array.

If the $pop operator removes the last item in the <field>, the <field> will then hold an empty array.

Starting in MongoDB 5.0, mongod no longer raises an error when you use an update operator like $pop with an empty operand expression ( { } ). An empty update results in no changes and no oplog entry is created (meaning that the operation is a no-op).

Examples

Remove the First Item of an Array

Create the students collection:

db.students.insertOne( { _id: 1, scores: [ 8, 9, 10 ] } )

The following example removes the first element, 8, from the scores array:

db.students.updateOne( { _id: 1 }, { $pop: { scores: -1 } } )

The first element, 8, has been removed from the scores array:

{ _id: 1, scores: [ 9, 10 ] }

Remove the Last Item of an Array

Add the following document to the students collection:

db.students.insertOne( { _id: 10, scores: [ 9, 10 ] } )

The following example removes the last element, 10, from the scores array by specifying 1 in the $pop expression:

db.students.updateOne( { _id: 10 }, { $pop: { scores: 1 } } )

The last element, 10, has been removed from the scores array:

{ _id: 10, scores: [ 9 ] }