title: EF core how to prevent duplicated values for a set of rows
body: <p>I'm looking for a way to prevent duplicated entries. This is my scenario:</p>
  <p>I have a model named Person</p>
  <pre class="lang-cs prettyprint-override"><code>    public class Person 
      {
          public int Id { get; set; }
          public string Name { get; set; }
          public string Surname { get; set; }
          public string Citizenship { get; set; }
      }
  </code></pre>
  <p>If I insert the first record with name John, surname Doe and citizenship American. Subsequently, if I insert another record as name John, surname Doe and citizenship French, I want EF Core to pick that up as a duplicate because we already have John Doe as an existing record.</p>