MongoDB dropIndex() Method (original) (raw)

Last Updated : 05 Feb, 2025

Indexes are important in MongoDB for improving query performance, allowing the database to quickly find the documents that match query criteria. The dropIndex() method in MongoDB enables developers to manage their **collection’s indexes by removing unnecessary or outdated indexes. However, it’s important to note that we cannot drop the default index on the **_id**field using this method.

In this article, we’ll explain the dropIndex() method in detail, its **syntax, **usage, **examples, and important considerations to help us manage indexes in MongoDB efficiently

What is the dropIndex() Method in MongoDB?

MongoDB **dropIndex() method allows for the removal of specified indexes from a **collection, but it does not permit the deletion of the default index of the **_id field. Additionally, **hidden indexes can also be dropped using this method. Starting from MongoDB 4.4, if the specified index is still being built, the dropIndex() method will **abort the building process of the index, providing developers with greater control over **index management in MongoDB collections.

Key points about the dropIndex() method:

• It removes a **single index at a time.
• It cannot remove the default _id index, as MongoDB automatically creates and requires this index.
• Starting from MongoDB **4.4, if an index is still being built, dropIndex() can abort the building process.
• Starting from MongoDB **4.2, we cannot drop all non-_id indexes using the db.Collection_Name.dropIndex("*") method. Instead, use the dropIndexes() method to remove multiple indexes.

**Syntax:

db.Collection_Name.dropIndex(index : <document/string>)

**Key Terms

• **collection_name: The name of the collection whose index we want to drop.
• **index: The index to drop. This can be specified either as a string (index name) or as a document (index specification)

Return Value of dropIndex()

The dropIndex() method returns a document with the following fields:

• **nIndexesWas: The number of indexes before the index was dropped.
• **ok: A value of 1 indicating the operation was successful.

**Example of Using MongoDB dropIndex() Method

Let’s walk through a few practical examples using MongoDB’s dropIndex() method. In these examples, we are working with:

• **Database: gfg
• **Collection: student
• **Document: Three documents contains name and language that students use in coding

Sample Documents in the student Collection:

Create an Index on the name Field

First of all we created an index on the name field using **createIndex() method:

db.student.createIndex({name:2})

This creates an ascending index on the name field. Now, let’s check the created index using the getIndexes() method.

db.student.getIndexes()

**Output:

**Explanation:

• The first index is the default _id index.
• The second index is the new name_1 index we just created on the name field.

**Example 1: Drop the Index Using the Index Name

To remove the index created on the **name**field, we can use the **index name (name_1) with the dropIndex() method.

**Query:

db.student.dropIndex("name_1")

**Output:

**Explanation:

• The index named name_1 on the name field is successfully dropped.
• nIndexesWas shows that the number of indexes before dropping the index was 2, and ok: 1 indicates the operation was successful.

**Example 2: Drop the Index Using the Index Specification Document

We can also drop the index using the **index specification document instead of the index name.

1. First, create an index on the name field with descending order.

db.student.createIndex({ name: -1 })

2. Now, drop the index by specifying the index document.

db.student.dropIndex({ name: -1 })

**Output:

**Explanation:

• The index on the name field with descending order (name: -1) is successfully dropped using the index specification document.
• As before, nIndexesWas shows the number of indexes before the operation (2), and ok: 1 confirms the success of the operation.

Key TakeAways About MongoDB dropIndex()

• **Single Index Deletion: The dropIndex() method removes one index at a time. To drop multiple indexes, use the dropIndexes() method.
• **Cannot Drop _id Index: MongoDB does not allow dropping the default _id index, which is essential for document identification.
• **Hidden Indexes: Hidden indexes, which are not used in query execution by default, can also be dropped using this method.
• **Abort Index Building (MongoDB 4.4+): If an index is still being built, dropIndex() can be used to abort the process.
• dropIndexes() for All Non- _id Indexes (MongoDB 4.2+): From MongoDB 4.2 onwards, you cannot use dropIndex("*") to drop all non-_id indexes. Instead, use dropIndexes() to drop multiple indexes.

Conclusion

The dropIndex() method in MongoDB is a vital tool for index management, allowing developers to remove unnecessary or outdated indexes, optimize database performance, and free up storage. Understanding when and how to use dropIndex() efficiently is key to managing a MongoDB database. From simple index deletions to handling hidden indexes and aborted index builds (starting in MongoDB 4.4), this method provides essential functionality for maintaining your MongoDB collections.