Cloud Firestore automatically creates indexes to support the most common types of queries, but allows you to define custom indexes and index overrides as described in the Cloud Firestore guides.

You can create, modify and deploy custom indexes in the Firebase console, or using the CLI. From the CLI, edit your index configuration file, with default filenamefirestore.indexes.json, and deploy using the firebase deploy command.

An index configuration file defines one object containing an indexes array and an optional fieldOverrides array. Here's an example:

{
  // Required, specify compound indexes
  indexes: [
    {
      collectionGroup: "posts",
      queryScope: "COLLECTION",
      fields: [
        { fieldPath: "author", arrayConfig: "CONTAINS" },
        { fieldPath: "timestamp", order: "DESCENDING" }
      ]
    }
  ],

  // Optional, disable indexes or enable single-field collection group indexes
  fieldOverrides: [
    {
      collectionGroup: "posts",
      fieldPath: "myBigMapField",
      // We want to disable indexing on our big map field, and so empty the indexes array
      indexes: []
    }
  ]
}

Deploy an index configuration

Deploy your index configuration with the firebase deploy command. By default, firebase deploy pushes all code and assets related to a Firebase project. If you only want to deploy indexes, add the --only firestore:indexes flag.

If you make edits to the indexes using the Firebase console, make sure you also update your local indexes file.

For more on managing indexes, see the Cloud Firestore guides.

JSON format

Indexes

The schema for one object in the indexes array is as follows. Optional properties are identified with the ? character.

Note that Cloud Firestore document fields can only be indexed in one mode, thus a field object cannot contain both the order and arrayConfig properties.

  collectionGroup: string  // Labeled "Collection ID" in the Firebase console
  queryScope: string       // One of "COLLECTION", "COLLECTION_GROUP"
  fields: array
    fieldPath: string
    order?: string         // One of "ASCENDING", "DESCENDING"; excludes arrayConfig property
    arrayConfig?: string   // If this parameter used, must be "CONTAINS"; excludes order property

FieldOverrides

The schema for one object in the fieldOverrides array is as follows. Optional properties are identified with the ? character.

Note that Cloud Firestore document fields can only be indexed in one mode, thus a field object cannot contain both the order and arrayConfig properties.

  collectionGroup: string  // Labeled "Collection ID" in the Firebase console
  fieldPath: string
  ttl?: boolean            // Set specified field to have TTL policy and be eligible for deletion
  indexes: array           // Set empty array to disable indexes on this collectionGroup + fieldPath
    queryScope: string     // One of "COLLECTION", "COLLECTION_GROUP"
    order?: string         // One of "ASCENDING", "DESCENDING"; excludes arrayConfig property
    arrayConfig?: string   // If this parameter used, must be "CONTAINS"; excludes order property

TTL Policy

A TTL policy can be enabled or disabled using the fieldOverrides array as it follows:

// Optional, disable index single-field collection group indexes
fieldOverrides: [
  {
    collectionGroup: "posts",
    fieldPath: "ttlField",
    ttl: "true", // Explicitly enable TTL on this Field.
    // Disable indexing so empty the indexes array
    indexes: [],
  },
];

To keep the default indexing in the field and enable a TTL policy:

{
  "fieldOverrides": [
    {
      "collectionGroup": "yourCollectionGroup",
      "fieldPath": "yourFieldPath",
      "ttl": true,
      "indexes": [
        { "order": "ASCENDING", "queryScope": "COLLECTION_GROUP" },
        { "order": "DESCENDING", "queryScope": "COLLECTION_GROUP" },
        { "arrayConfig": "CONTAINS", "queryScope": "COLLECTION_GROUP" }
      ]
    }
  ]
}

For more information about time-to-live (TTL) policies review the official documentation.