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$push

The $push operator appends a specified value to an array.

The $push operator has the form:

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

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

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.

If the field is absent in the document to update, $push adds the array field with the value as its element.

If the field is not an array, the operation will fail.

If the value is an array, $push appends the whole array as a single element. To add each element of the value separately, use the $each modifier with $push. For an example, see Append Multiple Values to an Array. For a list of modifiers available for $push, see Modifiers.

Starting in MongoDB 5.0, mongod no longer raises an error when you use an update operator like $push 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).

You can use the $push operator with the following modifiers:

Modifier
Description
Appends multiple values to the array field.
Limits the number of array elements. Requires the use of the $each modifier.
Orders elements of the array. Requires the use of the $each modifier.
Specifies the location in the array at which to insert the new elements. Requires the use of the $each modifier. Without the $position modifier, the $push appends the elements to the end of the array.

When used with modifiers, the $push operator has the form:

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

The processing of the $push operation with modifiers occur in the following order, regardless of the order in which the modifiers appear:

  1. Update array to add elements in the correct position.
  2. Apply sort, if specified.
  3. Slice the array, if specified.
  4. Store the array.

Create the students collection:

db.students.insertOne( { _id: 1, scores: [ 44, 78, 38, 80 ] } )

The following example appends 89 to the scores array:

db.students.updateOne(
{ _id: 1 },
{ $push: { scores: 89 } }
)

Example output:

{ _id: 1, scores: [ 44, 78, 38, 80, 89 ] }

Use $push with the $each modifier to append multiple values to the array field.

The following example appends each element of [ 90, 92, 85 ] to the scores array for the document where the name field equals joe:

db.students.updateOne(
{ name: "joe" },
{ $push: { scores: { $each: [ 90, 92, 85 ] } } }
)

Add the following document to the students collection:

db.students.insertOne(
{
"_id" : 5,
"quizzes" : [
{ "wk": 1, "score" : 10 },
{ "wk": 2, "score" : 8 },
{ "wk": 3, "score" : 5 },
{ "wk": 4, "score" : 6 }
]
}
)

The following $push operation uses:

  • the $each modifier to add multiple documents to the quizzes array,
  • the $sort modifier to sort all the elements of the modified quizzes array by the score field in descending order, and
  • the $slice modifier to keep only the first three sorted elements of the quizzes array.
db.students.updateOne(
{ _id: 5 },
{
$push: {
quizzes: {
$each: [ { wk: 5, score: 8 }, { wk: 6, score: 7 }, { wk: 7, score: 6 } ],
$sort: { score: -1 },
$slice: 3
}
}
}
)

After the operation only the three highest scoring quizzes are in the array:

{
"_id" : 5,
"quizzes" : [
{ "wk" : 1, "score" : 10 },
{ "wk" : 2, "score" : 8 },
{ "wk" : 5, "score" : 8 }
]
}
Tip
See also:
←  $pull$pullAll →
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