Implementing Composite Indexing in Firestore
1. What Is a Composite Index?
A composite index in Firestore is an index that includes multiple fields (two or more) in a specific order.
It allows Firestore to efficiently run complex queries such as:
Filtering on multiple fields
Combining filters with sort operations
Using inequality (<, <=, !=, >=) with orderBy
Querying on different fields that cannot be handled by built-in single-field indexes
Firestore automatically creates indexes for simple queries, but composite indexes must be added manually when a query needs them.
2. When Do You Need a Composite Index?
If you run a Firestore query that requires a composite index, Firestore returns an error like:
“FAILED_PRECONDITION: The query requires an index.”
The error includes a direct link to create the required composite index in the Firebase console.
Examples that require composite indexes:
A. Query with multiple where conditions
db.collection('products')
.where('category', '==', 'electronics')
.where('inStock', '==', true)
B. Filter + orderBy
db.collection('events')
.where('date', '>=', someDate)
.orderBy('date')
.orderBy('priority')
C. Using != or in with orderBy
db.collection('users')
.where('status', '!=', 'inactive')
.orderBy('status')
3. How to Create a Composite Index (Firestore Console)
Method 1: Use the Automatic Index Link (recommended)
Run the query in your app.
When Firestore throws a “requires index” error, click the link in the error message.
It takes you to the Firebase Console with pre-filled fields.
Click “Create Index”.
Wait for the index to build (typically a few seconds to minutes).
Method 2: Create Manually Through Firebase Console
Go to:
Firebase Console → Firestore Database → Indexes → Composite Indexes
Click “Add Index”.
Choose:
The collection
Fields to index
Sort direction: ASCENDING, DESCENDING, or ARRAY_CONTAINS
Add any filter fields and orderBy fields in the correct order.
Click Create.
4. Creating Composite Indexes via firestore.indexes.json (for deployment)
If you're using the Firebase CLI (recommended for teams), define indexes in the config file.
Example firestore.indexes.json
{
"indexes": [
{
"collectionGroup": "products",
"queryScope": "COLLECTION",
"fields": [
{ "fieldPath": "category", "order": "ASCENDING" },
{ "fieldPath": "price", "order": "DESCENDING" }
]
},
{
"collectionGroup": "events",
"queryScope": "COLLECTION",
"fields": [
{ "fieldPath": "date", "order": "ASCENDING" },
{ "fieldPath": "priority", "order": "ASCENDING" }
]
}
]
}
Deploy with:
firebase deploy --only firestore:indexes
5. Rules for Composite Indexes
✔ Ordering matters
Indexes must match the exact order of fields in the query.
✔ Inequality filters require an orderBy on the same field
Example:
.where('age', '>=', 18)
.orderBy('age')
✔ Limit, offset, and cursor queries still require appropriate indexes
Firestore applies pagination after indexing.
6. Best Practices
✔ Create indexes only when needed
Too many indexes can slow writes and increase storage cost.
✔ Use the provided error link
It ensures the index definition matches the query requirements exactly.
✔ Periodically remove unused indexes
From Indexes → Usage, delete unused ones to improve performance.
✔ Use collectionGroup indexes for queries across subcollections
7. Summary
Composite indexes in Firestore enable efficient querying when:
Filtering on multiple fields
Combining filtering and sorting
Using inequality or array operators
You can create them through:
Firebase Console (automatic or manual)
firestore.indexes.json via Firebase CLI
Composite indexes ensure your queries run quickly and reliably, especially for complex datasets.
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