Firebase Equivalent To NOT IN array

I am very new to both Firebase and Ionic and I am really confused. Is there a way we can exclude those blocked items in the results using Firebase like NOT IN array? The blocked items that I am talking about are the items that are saved in another table.

Below is a very basic structure :

    -how should I implement this

Thanks in advance…

you can get the key of the specific post, add it to *blocked_posts and assign it a value of true. Then, you can check to see if each post is in the blocked_posts table with

let checkTheseKeys = firebase.database().ref('posts');
let blockedKeys = firebase.database().ref('blocked_posts');

  checkTheseKeys.on("child_added", (snapshot) => {
     let checkThisKey = snapshot.key;
     let blockedCheck = blockedKeys.child(checkThisKey);
     blockedCheck.once("value", (snapshot) => {
         let doesExist = snapshot.exists();
         if (doesExist === true)  {
             //it's in blocked posts
             console.log('its blocked');
             }  else {
              //equivalent to not in array
               console.log("it's not in blocked posts")  

When doing something like this with Firebase, you’re not actually checking the value of the key you’re looking for, you’re just checking to see if the key exists.

I am by no means an expert on using firebase, but this type of action has worked for me in the past.