title: Apex and SOQL - upsert based on unique string field
body: <p>I am going to create several contact records by providing values only to the following fields.</p>
  
  <pre><code> Contact newCont = new Contact (FirstName = 'John',
                                  LastName = 'Smith',
                                  Email = 'john.smith@gmail.com');
  </code></pre>
  
  <p>The following should be unique.
            Email + FirstName + LastName
  so, I created a formula text field for this.</p>
  
  <p>I am thinking of executing an upsert so that I do not have to do several condition checks.
  How should I implement this ? what field should this upsert based on ?</p>
  
  <p>Regards</p>