title: Event value listener on parent with read rule in children
body: <p>I'm trying to make a database that has posts posted by a user and only persons subscribed to this person can see the post .
  the problem here is that I add an event listener on parent node on hope that it returns child nodes that only apply to the read rule written inside the children , I do know about the "Rules are not filters" section in the documentation of fire-base and I can't reach a good time/memory efficient design where I only retrieve posts that apply to my rules.
  That's my database </p>
  
  <pre><code>{
    "Users" : { // ids of users using the app
      "6Ya6nxqRy1fKt4BUOOh1brCJzvi2" : true,
      "Nxmo8Wlhlcg4GDvh7ZIAnmBbpS82" : true,
    },
    "followers" : {
      "6Ya6nxqRy1fKt4BUOOh1brCJzvi2" : { //followers to the user with this id 
        "Nxmo8Wlhlcg4GDvh7ZIAnmBbpS82" : false,
        "n9jTaFVPDNh6bJSSZZCT20UFA972" : true
      },
      "Nxmo8Wlhlcg4GDvh7ZIAnmBbpS82" : {
        "6Ya6nxqRy1fKt4BUOOh1brCJzvi2" : true,
        "n9jTaFVPDNh6bJSSZZCT20UFA972" : true
      }
    },
    "posts" : {
      "-M3YxODIv6frqFyGM4Nm" : { //post with a random generated Id
        "img" : "cd4aaff5-cab9-44d6-b7d9-7587ed2f19fc",
        "post" : "See this cool character !!",
        "user" : "Nxmo8Wlhlcg4GDvh7ZIAnmBbpS82"
      }
    }
  }
  </code></pre>
  
  <p>}
  and that's what i want to apply</p>
  
  <pre><code> {
   "rules": {
          ".write": true ,
          "posts":{
           "$pid":{
               ".read": "data.child('user').val()===auth.uid ||root.child('followers').child(auth.uid).child(data.child('user').val()).val()=== true "
             }
          },
          "followers":{
                ".read": true
          },
          "Users":{    
                ".read": true,
          }
       }
   }
  </code></pre>
  
  <p>the problem arises when I want to add event listener on "posts" node but as it doesn't have read : true so it doesn't return anything.</p>
  
  <p>the only solution I could think of was to make another tree on same level of posts which will contain all posts names and then i start making single event listener on each post node (replace child(posts) to child(posts + post[i] ))</p>
  
  <p>Is there any better option because in case of 100 post I will make 100 single event task which I think of as time ,memory and Internet unnecessary consuming </p>