title: ForeignKey SetNull OnDelete
body: <p>I would like to know if it possible, with a composite foreign key, to set only one column of this foreign key to null when I delete related row.</p>
  
  <p>Indeed, the second column (the one i don't want to be null) is used for other foreign keys that I don't want to be deactivated. </p>
  
  <p>Precision : I use Entity framework Core (last version).</p>