title: SQLAlchemy filter query by conditions in multiple table
body: <p>I am writing a Flask webapp and having a hard time with SQLAlchemy.  I am very new to SQLAlchemy and Flask.</p>
  
  <p>I have following three tables.</p>
  
  <pre><code>User:
  [
     user_id
     first_name
     last_name
  ]
  
  Picture:
  [
     filename
     picture_type // eg: painting, photograph
     painter
  ]
  
  Comment
  [
     user_id
     filename
     comment
  ]
  </code></pre>
  
  <p>I am trying to query all filenames that was not reviewed by current user.
  So the condition would be "all filenames from the picture table with matching picture type where each filename should not have matching, in Comment table, filename and matching user_id with the current user</p>
  
  <p>Currently the current user user_id an picture_type information are available as incoming argument to the function I am trying to write.</p>
  
  <p>How should I write the query using session filter query?</p>