$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¶

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.

Examples¶

Remove the First Item of an Array¶

Given the following document in a collection students:

{ _id: 1, scores: [ 8, 9, 10 ] }

The following example removes the first element (8) in the scores array:

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

After the operation, the updated document has the first item 8 removed from its scores array:

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

Remove the Last Item of an Array¶

Given the following document in a collection students:

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

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

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

After the operation, the updated document has the last item 10 removed from its scores array:

{ _id: 1, scores: [ 9 ] }

参见

db.collection.update(), db.collection.findAndModify()

← $addToSet $pullAll →