Firebase - 按孙节点键查询问题求助

Hey there! Let's work through this Firebase database structure and query issue. First, I can guess that your current setup probably nests user IDs inside each list, which makes it hard to reverse-engineer "all lists that include id1"—since Firebase Realtime Database (and Firestore, for that matter) doesn't support deep cross-queries efficiently.

Let's start with a common problematic structure (what I suspect you might have): #

{
  "lists": {
    "idList1": {
      "name": "Weekly Groceries",
      "users": {
        "id1": "Alice",
        "id3": "Charlie"
      }
    },
    "idList2": {
      "name": "Project Milestones",
      "users": {
        "id1": "Alice"
      }
    },
    "idList3": {
      "name": "Fitness Goals",
      "users": {
        "id2": "Bob"
      }
    }
  }
}

The problem here is that to find all lists with id1, you'd have to load every single list and check if users/id1 exists—super inefficient, especially as your dataset grows.

The Fix: Denormalize with a Reverse Index #

Firebase thrives when you structure data for the queries you actually need. For your use case, add a reverse index that maps user IDs directly to the lists they're part of. Here's the optimized structure:

{
  "lists": {
    "idList1": {
      "name": "Weekly Groceries",
      "users": {
        "id1": true,
        "id3": true
      }
    },
    "idList2": {
      "name": "Project Milestones",
      "users": {
        "id1": true
      }
    },
    "idList3": {
      "name": "Fitness Goals",
      "users": {
        "id2": true
      }
    }
  },
  "userToLists": {
    "id1": {
      "idList1": true,
      "idList2": true
    },
    "id2": {
      "idList3": true
    },
    "id3": {
      "idList1": true
    }
  }
}

This way, you get two key benefits:

• You can instantly fetch all list IDs for id1 from userToLists/id1
• You can still verify which users are in a list by checking the users node of each list

How to Query for id1's Lists (Realtime Database) #

Here's a JavaScript example to get exactly what you need (idList1 and idList2):

// Step 1: Get all list IDs associated with id1
firebase.database().ref('userToLists/id1').once('value')
  .then(snapshot => {
    const listIds = Object.keys(snapshot.val());
    // Step 2: Fetch details for each list ID
    const fetchListPromises = listIds.map(listId => 
      firebase.database().ref(`lists/${listId}`).once('value')
    );
    return Promise.all(fetchListPromises);
  })
  .then(listSnapshots => {
    const userLists = listSnapshots.map(snap => ({
      id: snap.key,
      ...snap.val()
    }));
    console.log('Lists for id1:', userLists);
    // Output will include idList1 and idList2 with their full details
  })
  .catch(err => console.error('Error fetching lists:', err));

If You're Using Firestore (Alternative) #

If you're on Firestore instead of Realtime Database, the approach is similar but uses collections and documents. Here's a recommended structure:

• A lists collection where each document has a userIds field (a map of { [userId]: true })
• (Optional) A userLists collection where each document (keyed by user ID) has an array or map of list IDs

To query lists containing id1 in Firestore:

firebase.firestore().collection('lists')
  .where('userIds.id1', '==', true)
  .get()
  .then(querySnapshot => {
    const userLists = [];
    querySnapshot.forEach(doc => {
      userLists.push({ id: doc.id, ...doc.data() });
    });
    console.log('Lists for id1:', userLists);
  })
  .catch(err => console.error('Error fetching lists:', err));

Key Takeaway #

Firebase NoSQL databases aren't designed like traditional SQL databases—you need to model your data around the queries you want to run. Adding a reverse index eliminates the need for inefficient full-dataset scans and makes your query fast and scalable.

内容的提问来源于stack exchange，提问作者ozzem