How to Use $pop Operator in MongoDB: Syntax and Examples

The $pop operator in MongoDB removes the first or last element from an array field in a document. Use { $pop: { field: 1 } } to remove the last element and { $pop: { field: -1 } } to remove the first element.

Syntax

The $pop operator is used inside an update command to remove an element from an array.

• field: The name of the array field to modify.
• 1: Removes the last element of the array.
• -1: Removes the first element of the array.

mongodb

db.collection.updateOne(
  { <filter> },
  { $pop: { <field>: 1 } }  // removes last element
)

// or

db.collection.updateOne(
  { <filter> },
  { $pop: { <field>: -1 } } // removes first element
)

Example

This example shows how to remove the last and first element from an array field named scores in a document.

mongodb

db.students.insertOne({ name: "Alice", scores: [85, 90, 95] })

// Remove last element (95)
db.students.updateOne(
  { name: "Alice" },
  { $pop: { scores: 1 } }
)

// Document after update: { name: "Alice", scores: [85, 90] }

// Remove first element (85)
db.students.updateOne(
  { name: "Alice" },
  { $pop: { scores: -1 } }
)

// Document after update: { name: "Alice", scores: [90] }

Output

{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }
{ "name" : "Alice", "scores" : [ 85, 90 ] }
{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }
{ "name" : "Alice", "scores" : [ 90 ] }

Common Pitfalls

Common mistakes when using $pop include:

• Using values other than 1 or -1 which are ignored.
• Applying $pop on fields that are not arrays causes no change.
• Expecting $pop to remove multiple elements; it only removes one element per update.

mongodb

/* Wrong: Using 2 instead of 1 or -1 */
db.students.updateOne(
  { name: "Alice" },
  { $pop: { scores: 2 } }  // Ignored, no change
)

/* Correct: Use 1 or -1 */
db.students.updateOne(
  { name: "Alice" },
  { $pop: { scores: 1 } }  // Removes last element
)

Quick Reference

Usage	Value	Effect
Remove last element	1	Removes the last element from the array
Remove first element	-1	Removes the first element from the array

Key Takeaways

Use $pop with 1 to remove the last element of an array field.

Use $pop with -1 to remove the first element of an array field.

Only one element is removed per update operation with $pop.

Using values other than 1 or -1 for $pop has no effect.

Ensure the target field is an array before using $pop.