firestore.indexes.json

{
    "indexes": [
        {
            "collectionGroup": "chat_messages",
            "queryScope": "COLLECTION",
            "fields": [
                {
                    "fieldPath": "chat",
                    "order": "ASCENDING"
                },
                {
                    "fieldPath": "timestamp",
                    "order": "DESCENDING"
                }
            ]
        },
        {
            "collectionGroup": "chats",
            "queryScope": "COLLECTION",
            "fields": [
                {
                    "fieldPath": "users",
                    "arrayConfig": "CONTAINS"
                },
                {
                    "fieldPath": "last_message_time",
                    "order": "DESCENDING"
                }
            ]
        },
        {
            "collectionGroup": "participants",
            "queryScope": "COLLECTION",
            "fields": [
                {
                    "fieldPath": "activityRef",
                    "order": "ASCENDING"
                },
                {
                    "fieldPath": "created_at",
                    "order": "DESCENDING"
                }
            ]
        }
    ]
}