firestore.indexes.json

{
  "indexes": [
    {
      "collectionGroup": "signUps",
      "queryScope": "COLLECTION_GROUP",
      "fields": [
        {
          "fieldPath": "eventId",
          "order": "ASCENDING"
        },
        {
          "fieldPath": "volunteerUid",
          "order": "ASCENDING"
        }
      ]
    }
  ],
  "fieldOverrides": [
    {
      "collectionGroup": "signUps",
      "fieldPath": "eventId",
      "ttl": false,
      "indexes": [
        {
          "order": "ASCENDING",
          "queryScope": "COLLECTION"
        },
        {
          "order": "DESCENDING",
          "queryScope": "COLLECTION"
        },
        {
          "arrayConfig": "CONTAINS",
          "queryScope": "COLLECTION"
        }
      ]
    },
    {
      "collectionGroup": "signUps",
      "fieldPath": "volunteerUid",
      "ttl": false,
      "indexes": [
        {
          "order": "ASCENDING",
          "queryScope": "COLLECTION"
        },
        {
          "order": "DESCENDING",
          "queryScope": "COLLECTION"
        },
        {
          "arrayConfig": "CONTAINS",
          "queryScope": "COLLECTION"
        }
      ]
    }
  ]
}