title: can not connect to PostgreSQL database using npgsql
body: <p>I tried 10 different npgsql version and entity framework using visual studio 2017 to get connected to PostgreSQL database but every time  I get this error:</p>
  
  <blockquote>
    <p>Could not load file or assembly "System.ValueTuple,version=4.0.3.0 </p>
  </blockquote>
  
  <p>Even if I install this, I still get the same error. Any idea?</p>