如何在Firebase中遍历子记录？获取users表sent_request的user_keys

It looks like you're trying to fetch the sent_request child nodes for a specific user but aren't getting the expected output. Let's break down what might be going wrong and how to fix it.

Common Issues in Your Current Code #

1. sent_request is an Object, Not an Array: Firebase Realtime Database stores collections as objects (with auto-generated or custom keys) rather than arrays. Your current code overwrites the empty sent_request array with this object, but logging it directly might not display the user keys in a readable format, or you may not be explicitly extracting the keys you need.
2. Missing Null/Undefined Checks: If the user has no sent requests, item.val().sent_request could be null or undefined, leading to unexpected behavior or errors.

Corrected Code #

Here's an updated version of your function that addresses these issues and properly extracts the user keys from sent_request:

getProfileData(emailID) {
  const ref = firebase.database().ref('users');
  ref.orderByChild("email").equalTo(emailID).once("value", (items) => {
    let sentRequestKeys = [];
    
    items.forEach((item) => {
      const sentRequests = item.val().sent_request;
      
      // Check if sent_request exists and is an object before processing
      if (sentRequests && typeof sentRequests === 'object') {
        // Convert the Firebase object into an array of user keys
        sentRequestKeys = Object.keys(sentRequests);
        
        // If you need access to the values associated with each key too, use this:
        // const sentRequestDetails = Object.entries(sentRequests);
        // sentRequestDetails.forEach(([key, value]) => {
        //   console.log(`User Key: ${key}, Request Data:`, value);
        // });
      }
    });
    
    console.log("Sent Request User Keys:", sentRequestKeys);
  }).catch((error) => {
    // Handle any database query errors (e.g., permission issues)
    console.error("Error fetching profile data:", error);
  });
}

Key Improvements #

• Explicit Key Extraction: Using Object.keys(sentRequests) converts the Firebase collection object into an array of user keys, which is likely what you're expecting to see.
• Null Safety: We add checks to ensure sentRequests exists and is an object before processing, preventing runtime errors.
• Error Handling: Added a .catch() block to log any issues that occur during the database query (like invalid permissions or incorrect paths).
• Readability: Renamed variables for clarity and added comments to explain each step.

Additional Notes #

• Since email addresses should be unique in your users table, you could also access the user directly with const user = Object.values(items.val())[0] instead of using forEach, but forEach remains safe if there's a chance of multiple matches (though you should enforce unique emails in your database rules).
• If your sent_request structure is intentionally an array (uncommon in Firebase, as arrays are not recommended for dynamic collections), you can skip the Object.keys() step and use sentRequests directly.

内容的提问来源于stack exchange，提问作者Shreyas Pednekar