Firestore: 9 FAILED_PRECONDITION: The query requires an index. You can create it here: https://console.firebase.google.com/...

Meaning

Click the link in the error (it pre-fills the index) or add it to firestore.indexes.json and deploy. Queries with equality on one field and range/order on another, or multiple orderBy, need composite indexes. Index builds take a few minutes.

Common causes

• Composite query without a composite index
• Range filter on one field with orderBy on another
• Index still building
• Index deleted or collection group scope wrong
• Query changed after deploy

Detailed fix by platform

Code examples

{
  "indexes": [{
    "collectionGroup": "orders",
    "queryScope": "COLLECTION",
    "fields": [
      { "fieldPath": "userId", "order": "ASCENDING" },
      { "fieldPath": "createdAt", "order": "DESCENDING" }
    ]
  }]
}

How to diagnose

1. Query — Filters and orderBy?
2. Index — Exists, built?
3. Scope — Collection vs group?

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