$pop
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Definition
$popThe
$popoperator removes the first or last element of an array. Pass$popa value of-1to remove the first element of an array and1to remove the last element in an array.The
$popoperator 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 ] }