title: EF Core CSV Upload Check if data exists takes a lot of time
body: <p>I am currently parsing a CSV file with 15.000+ lines. I need to insert all of them in my database, but every line contains data that need to be inserted to multiple entites. </p>
  
  <p>The problem that I have is that I need to check for each line if the data exists already in my database, if not I insert it with BulkInsert at the end.</p>
  
  <p>But it takes a lot of time to check for each line if the data exists already (entites.FirstOrDefault(...))... I mean it "only" takes 30-50ms to check if it exists, but to do this 15.000+ times, ends up taking several minutes for the whole operation.</p>
  
  <p>Do you have any suggestions ? </p>