title: Firestore Security Rule Get in Function
body: <p>I have the following rule which works:</p>
  
  <pre><code>match /databases/{database}/documents {
    match /item/{itemId} {
      allow read:get(/databases/$(database)/documents/properties/$(resource.data.propertyId)).data.users[request.auth.uid] == true)
    }
  }
  </code></pre>
  
  <p>I would like to make this a function such as:</p>
  
  <pre><code>function isPropertyMember() {
    return get(/databases/$(database)/documents/properties/$(resource.data.propertyId))
    .data.users[request.auth.uid] == true
  }
  </code></pre>
  
  <p>allow read: if isPropertyMember()</p>
  
  <p>With the same query from the same user data is returned on the query when not in the function. When I move it to the function I get "Missing or insufficient permission" error.</p>