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MongoDB - Positional Operator ($)

Last Updated : 12 Jul, 2025

MongoDB provides a variety of array update operators to modify the values within array fields in documents. One such operator is the positional operator $. This operator allows us to update an element in an array without explicitly specifying the position of that element. In this article, We will learn about the Positional Operator($) in MongoDB in detail.

MongoDB provides different types of array update operators to update the values of the array fields in the documents and the positional operator() is one of them.

The $ operator can be used with arrays containing embedded documents which allows us to update fields within those nested documents efficiently.

Syntax:

{ "<array>.$" : value }

• We cannot use the $ operator with upsert operations. If we use $ operator with upsert operations, then the insert will use the $ as a field name in the inserted document.
  
• This operator cannot use for those queries which traverse more than one array because the replacement for the $ placeholder is a single value.
  
• When we use the $ operator with $unset operator then $ operator does not remove the matching item from the array, but rather sets it to null.
  
• When a query matches the array with the help of negation operators like $not, $ne, or $nin, then you cannot use the $ operator to update the values of that array. And if the negated part of the query is present inside of an $elemMatch expression then we can use the positional $ operator to update this field.
  
• When we use this operator with an update operation like db.collection.update() and db.collection.findAndModify() then the $ operator works as a placeholder for the first item that matches the query document and the array field is necessary to appear as a part of the query document.

In the following examples, we are working with called contributor which contains various information in terms of documents as shown below:

Output:

In this example, we are updating the first item whose value is "Python" to "Ruby" in the language field with the help of $ operator, because we don't know the position of the item in the array.

db.contributor.updateOne({name: "Rohit", language: "Python"}, 
                         {$set: {"language.$": "Ruby"}})

Output:

Here, the $ operator is working as a placeholder for the first match of the update query document.

Note: The array field must be the part of the query.

In this example, we are updating an array that contains embedded documents with the help of $ operator and to access embedded document fields we use dot notation. Or in other words, we are updating the value of tArticle field from 60 to 100.

db.contributor.updateOne({name: "Rohit", "articles.language": "C#"}, 
                         {$set: {"articles.$.tArticles": 100}})

Output:

In this example, we are updating the value of the tArticles field in the first embedded document that has a pArticles field with a value greater than 90.

db.contributor.updateOne({name: "Sumit", articles: {$elemMatch:
                                          {pArticles: {$gt: 30}}}},
                             {$set: {"articles.$.tArticles": 200}})

Output:

The MongoDB positional operator $ is a powerful tool for updating elements within arrays when the exact position is unknown. By acting as a placeholder for the first matching element, it simplifies the update process. However, it comes with limitations such as not being usable with upsert operations or queries involving negation operators. Understanding these nuances can help effectively use the $ operator for various array update operations in MongoDB.

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