AngularFire2中Firebase推送对象至数组的存储格式问题

Hey there! I get it—you want your Books node to use numeric indices (like 0: {...}, 1: {...}) to mimic an array for easier traversal, but right now Firebase is auto-generating those random push IDs. Let's walk through how to adjust your code and cover some important caveats.

Why Firebase Uses Push IDs (Quick Context) #

First, a quick note: Firebase's push IDs are designed to solve concurrent write conflicts—if multiple users add data at the same time, push IDs ensure no two entries overwrite each other. But if your use case specifically requires numeric indices (like single-user apps or controlled write flows), we can make that work.

Solution 1: Manual Numeric Indices (Single-User Scenarios) #

If you're only dealing with one user writing to the Books node at a time, you can fetch the current number of entries and use that as the next index:

// Assume your Firebase Realtime Database reference is set up as `db`
const booksRef = db.ref('Books');

// Step 1: Get the current count of books
booksRef.once('value')
  .then(snapshot => {
    const nextIndex = snapshot.numChildren(); // This gives you the length of the "array"
    const book_data = { 
      id: bookId, 
      name: bookData.name, 
      author: bookData.author, 
      genre: bookData.genre
      // Add any other fields you need
    };
    // Step 2: Write the book to the new index
    return booksRef.child(nextIndex).set(book_data);
  })
  .then(() => {
    console.log('Book added successfully at index!');
  })
  .catch(error => {
    console.error('Error adding book:', error);
  });

Solution 2: Concurrent-Safe Indices (Multi-User Scenarios) #

If multiple users might add books at the same time, the above approach can cause conflicts (two users could grab the same index and overwrite each other). For this, use Firebase's transaction to safely generate the next index:

const book_data = { 
  id: bookId, 
  name: bookData.name, 
  author: bookData.author, 
  genre: bookData.genre
};

booksRef.transaction(currentBooks => {
  if (!currentBooks) {
    // If Books node doesn't exist yet, initialize with the first book at index 0
    return { 0: book_data };
  } else {
    // Calculate next index from the number of existing entries
    const nextIndex = Object.keys(currentBooks).length;
    currentBooks[nextIndex] = book_data;
    return currentBooks;
  }
})
.then(result => {
  if (result.committed) {
    console.log('Book added safely (no conflicts)!');
  } else {
    console.log('Transaction aborted—another write happened at the same time');
  }
})
.catch(error => {
  console.error('Transaction failed:', error);
});

A Quick Alternative: Keep Push IDs, Traverse Easily #

Just a thought—you don't have to use numeric indices to traverse data easily. Firebase lets you loop through push ID entries just like an array:

booksRef.on('value', snapshot => {
  snapshot.forEach(childSnapshot => {
    const book = childSnapshot.val();
    // Process each book here (e.g., render to UI)
    console.log(`Book: ${book.name} by ${book.author}`);
  });
});

If you need ordered data, you can also add a timestamp or order field to each book and use orderByChild('timestamp') to sort results.

内容的提问来源于stack exchange，提问作者Carlos Martel Lamas