MongoDB $push Operator
MongoDB $push operator appends a value to the already existing array within a document.
$push Operator in MongoDB
The $push operator in MongoDB is used to update the array in MongoDB. It inserts a new value into the array in the specific index.
If the mentioned field is absent in the document to update, the $push operator adds it as a new field and includes the mentioned value as its element.
If the value is an array, the $push operator appends the whole array as a single element. To add each element of the value separately, the $push operator can be used with the $each modifier.
Syntax
The syntax for using the $push operator is:
{ $push: { <field1>: <value1>, ... } }
Here, <field> can specify with dot notation in embedded/nested documents or an array.
We can also use the modifiers with the $push operator:
Syntax:
{ $push: { <field1>: { <modifier1>: <value1>, ... }, ... } }
The processing of the push operation with modifiers works in the following order:
- First update the array to add items in the correct position.
- Second, apply sort if specified.
- Third slice the array if specified.
- Fourth store the array.
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.
Modifier | Description |
---|---|
$each | It is used to append multiple values to the array field. |
$slice | It is used to limit the number of array items and require the use of the $each modifier. |
$sort | It is used to order items of the array and require the use of the $each modifier. |
$position | It is used to specify the location in the array at which to insert the new items and require the use of the $each modifier. If the $push operator does not use $position modifier, then this operator will append the items to the end of the array. |
MongoDB $push Operator
In the following examples, we are working with
Database: w3wiki
Collection: contributor
Document: two documents that contain the details of the contributor in the form of field-value pairs
Appending a single value to an array example using $push operator
In this example, we are appending a single value, i.e., “C++” to an array field, i.e., language field in the document that satisfy the condition(name: “Rohit”).
Query:
db.contributor.update({name: "Rohit"}, {$push: {language: "C++"}})
Output:
Appending multiple values to an array using $push operator
In this example, we are appending multiple values, i.e., [“C”, “Ruby”, “Go”] to an array field, i.e., language field in the document that satisfy the condition(name: “Sumit”).
Query:
db.contributor.update({name: "Sumit"}, {$push: {language: {$each: ["C", "Ruby", "Go"]}}})
Output:
Appending multiple values to an array in the nested/embedded document using $push operator:
In this example, we are appending multiple values, i.e., [89, 76.4] to an array field, i.e., personal.semesterMarks field of a nested/embedded document.
Query:
db.contributor.update({name: "Sumit"},
{$push: {"personal.semesterMarks": {$each: [89, 76.4]}}})
Output:
Using modifiers with $push operator example
In this example, we are using multiple modifiers like $each, $sort, and $slice with $push operator.
Query:
db.contributor.update({name: "Rohit"},
{$push: { language: { $each: ["C", "Go"],
$sort: 1, $slice: 4}}})
Here,
- The $each modifier is used to add multiple documents to the language array.
- The $sort modifier is used to sort all the items of the modified language array in ascending.
- The $slice modifier is used to keep only the first four sorted items of the language array.
Output:
KeyTakeAways About MongoDB $push Operator
- The $push operator in MongoDB is used append a new value into the array in the specific index.
- If the specified field in the $push operator is not present in the document, then this operator will add the array field with the value as its items.
- You can use this operator with methods like update(), findAndModify(), etc., according to your requirements.
- The $push operator inserts items at the end of the array.
- If the specified field in the $push operator is not an array, then this operation will fail.
- If the value of the $push the operator is an array, then this operator will append the whole array as a single element. And if you want to add each item of the value separately, then you can use $each modifier with $push the operator.