title: Check Firestore data for the existence of each element in an array
body: <p>I am trying to query on a single node that has the following structure:</p>
  
  <pre><code>//object in firestore    
  fruit = {"Orange","Apple","Pineapple","Banana","Grapes"}
  </code></pre>
  
  <p>Now my logic is setup that I have an array, let's say we have two items in the array like this </p>
  
  <pre><code>//object in my code
  fruit:any = ["Pineapple","Grapes"];
  </code></pre>
  
  <p>and I want to check if the items in the array exist under fruit in the database, I do the following query</p>
  
  <pre><code>    checkFruits(uid,fruit):Observable&lt;any&gt;{
          //console.log(fruit);
          return this.afs.collection('profiles').doc(uid).collection(`fruit`, ref =&gt; ref.
          //what to do here to make it check for each item in fruit array ??
          where(`fruit.${fruit}`, '==', true)).valueChanges(); 
           }
  </code></pre>
  
  <p>I cant quite wrap my head around how to to check the existence of each element in my array under fruit object.</p>