MongoDB $push Operator

The $push operator in MongoDB adds values to an array field during updates, creating the field if it doesn’t exist, and can insert multiple values individually when used with $each.

• Appends a new value to the end of the array by default (can insert at a specific position using modifiers like $position).
• Automatically creates the array field if it is missing.
• Treats an input array as a single element unless $each is used.
• Supports adding multiple elements individually with the $each modifier.

Syntax

{ $push: { <field1>: <value1>, ... } }

• <field> can target an array field and supports dot notation for embedded/nested documents.
• <value> is the element to be added to the array.

Syntax with Modifiers

{ $push: { <field1>: { <modifier1>: <value1>, ... }, ... } }

• Modifiers like $each, $position, $sort, and $slice can be used with $push.

Processing Order with Modifiers

• First, items are added to the array at the specified position.
• Then, sorting is applied if $sort is specified.
• Next, the array is sliced if $slice is specified.
• Finally, the updated array is stored.

Note: Here the order in which the modifiers appear in the $push operator does not matter.

List of $push operator modifiers

Below are the modifiers in MongoDB that can be used with $push operator.

Examples of MongoDB $push Operator

In the following examples, we are working with

Database: GeeksforGeeks
Collection: contributor
Document: Two documents that contain the details of the contributor in the form of field-value pairs

Example 1: Append a Value to an Array

Appending a single value, i.e., "C++" to an array field, i.e., language field in the document that satisfies the condition(name: "Mateo").

db.contributor.updateOne({ name: "Mateo" }, { $push: { language: "C++" } })

Output:

Example 2: Append Multiple Values to an Array

Appending multiple values, i.e., ["C", "Ruby", "Go"] to an array field, i.e., language field in the document that satisfy the condition (name: "Luca").

db.contributor.updateOne({ name: "Luca" }, { $push: { language: { $each: ["C", "Ruby", "Go"] } } })

Output:

Example 3: Append Multiple Values to embedded document

Appending multiple values, i.e., [89, 76.4] to an array field, i.e., personal.semesterMarks field of a nested/embedded document.

db.contributor.updateOne(
 { name: "Luca" },
 {
 $push: {
 "personal.semesterMarks": {
 $each: [89, 76.4]
 }
 }
 }
)

Output:

Example 4: Use $push Operator with Multiple Modifiers

Adds multiple values to an array, then sorts and limits the array size by truncating elements after sorting or insertion in one atomic update.

db.contributor.updateOne(
 { name: "Mateo" },
 {
 $push: {
 language: {
 $each: ["C", "Go"],
 $sort: 1,
 $slice: 4
 }
 }
 }
)

Output:

• The $each modifier adds multiple elements to the language array.
• The $sort modifier sorts the modified language array in ascending order.
• The $slice modifier retains only the first four elements by index.

Usage of $push Operator

Here are some uses of $push operator:

• Append new elements to arrays at the last index without replacing the document.
• Initialize the array field automatically if it doesn’t exist.
• Add multiple values using $each, inserting each item at a new index.
• Control insertion position and ordering with $position, $sort, and limit array size with $slice.
• Use with updateOne(), updateMany(), and findOneAndUpdate() to perform atomic, in-place updates on matched documents.