📋

Description

This error indicates that MongoDB could not locate an index required for a specific operation. It commonly occurs when querying, updating, or attempting to drop an index that does not exist or has been referenced incorrectly.

💬

Error Message

Index Not Found

🔍

Known Causes

4 known causes

⚠️

Index Does Not Exist

The specified index was never created on the collection, or it was previously dropped and is no longer available.

⚠️

Incorrect Index Name

The application code or administrative command references an index name that does not precisely match any existing index on the target collection.

⚠️

Wrong Collection or Database Context

The operation is being performed against a collection or database where the intended index does not reside, or the connection context is incorrect.

⚠️

Index Dropped Unexpectedly

The index might have been dropped by another process, user, or during a schema migration, making it unavailable for subsequent operations.

🛠️

Solutions

4 solutions available

1. Verify Index Existence easy

Check if the expected index actually exists in the collection.

1

Connect to your MongoDB instance using the `mongosh` shell.

mongosh

2

Switch to the database where the collection resides.

use your_database_name

3

List all indexes for the specific collection.

db.your_collection_name.getIndexes()

4

Examine the output to confirm if the required index (based on the field(s) used in your query) is present. The index name or the field(s) it covers should match what your query expects.

[
  { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_" },
  { "v" : 2, "key" : { "your_field" : 1 }, "name" : "your_field_1" }
]

2. Create the Missing Index easy

If the index is confirmed to be missing, create it.

1

Connect to your MongoDB instance using the `mongosh` shell.

mongosh

2

Switch to the database where the collection resides.

use your_database_name

3

Create the necessary index. Replace `your_collection_name`, `your_field`, and `1` (for ascending order, `-1` for descending) with your actual collection name, field name, and desired sort order.

db.your_collection_name.createIndex({ your_field: 1 })

4

For compound indexes, specify multiple fields.

db.your_collection_name.createIndex({ field1: 1, field2: -1 })

5

After creation, re-run your query. It should now find the index and execute successfully.

db.your_collection_name.find({ your_field: 'some_value' })

3. Review Query Logic for Index Usage medium

Ensure your query is structured in a way that can utilize an existing index.

1

Examine the query that is causing the 'Index Not Found' error. Identify the fields used in the `find()`, `sort()`, and `aggregate()` stages.

db.your_collection_name.find({ 'user.id': 123 }).sort({ 'timestamp': -1 })

2

Check if an index exists that covers all the fields in the `find()` clause and the first field in the `sort()` clause (for queries involving both). MongoDB can often use a single index for both filtering and sorting if it's structured appropriately.

db.your_collection_name.getIndexes()

3

If your query uses fields that are not part of any existing index, or if the index order doesn't match the query's needs, consider creating a new index that better aligns with your query patterns.

db.your_collection_name.createIndex({ 'user.id': 1, 'timestamp': -1 })

4

For more complex queries, especially those using aggregation pipelines, analyze the execution plan using `explain()` to understand how MongoDB is processing the query and identify potential index bottlenecks.

db.your_collection_name.aggregate([...]).explain('executionStats')

4. Check for Typographical Errors in Field Names easy

A simple typo in a field name can lead to an index not being found.

1

Carefully review the field names used in your query.

db.your_collection_name.find({ 'user_id': 123 })

2

Compare these field names with the actual field names in your MongoDB documents and the names of your existing indexes.

db.your_collection_name.findOne()

3

Pay attention to case sensitivity and underscores. For example, `userId` is different from `user_id`.

db.your_collection_name.getIndexes()

4

If a typo is found, correct it in your query and re-execute.

db.your_collection_name.find({ 'userId': 123 })

🔗

Related Errors

5 related errors

MongoDB Error 27: Index Not Found