title: What is the replacement for hasRequired with EF core?
body: <p>With Entity Framework we had <code>HasRequired</code> on a field. What is the alternative replacement for that with EF core?</p>
  <p><a href="https://msdn.microsoft.com/en-us/library/jj591620(v=vs.113).aspx" rel="noreferrer">https://msdn.microsoft.com/en-us/library/jj591620(v=vs.113).aspx</a></p>
  <p>I tried with <code>HasRequired</code> but it throws error.</p>