$in

Compatibility

You can use $in for deployments hosted in the following environments:

• MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud

• MongoDB Enterprise: The subscription-based, self-managed version of MongoDB

• MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB

Syntax

To specify an $in expression, use the following prototype:

{ field: { $in: [<value1>, <value2>, ... <valueN> ] } }

For comparison of different BSON type values, see the specified BSON comparison order.

If the field holds an array, then the $in operator selects the documents whose field holds an array that contains at least one element that matches a value in the specified array (for example, <value1>, <value2>, and so on).

The $in operator compares each parameter to each document in the collection, which can lead to performance issues. To improve performance:

• It is recommended that you limit the number of parameters passed to the

  $in operator to tens of values. Using hundreds of parameters or more can negatively impact query performance.

• Create an index on the field you want to query.

Query Data on Atlas by Using Atlas Search

For data stored in MongoDB Atlas, you can use the Atlas Search in Operator operator when running $search queries. Running $in after $search is less performant than running $search with the in Operator operator.

To learn more about the Atlas Search version of this operator, see the in Operator operator in the Atlas documentation.

Examples

Use the $in Operator to Match Values

Consider the following example:

db.inventory.find( { qty: { $in: [ 5, 15 ] } } )

This query selects all documents in the inventory collection where the qty field value is either 5 or 15. Although you can express this query using the $or operator, choose the $in operator rather than the $or operator when performing equality checks on the same field.

Use the $in Operator to Match Values in an Array

The collection inventory contains documents that include the field tags, as in the following:

{ _id: 1, item: "abc", qty: 10, tags: [ "school", "clothing" ], sale: false }

Then, the following update() operation will set the sale field value to true where the tags field holds an array with at least one element matching either "appliances" or "school".

db.inventory.update(
                     { tags: { $in: ["appliances", "school"] } },
                     { $set: { sale:true } }
                   )

For additional examples in querying arrays, see:

• Query an Array

• Query an Array of Embedded Documents

For additional examples in querying, see:

• Query Documents

db.inventory.find( { tags: { $in: [ /^be/, /^st/ ] } } )