title: Return bool value if it exists in Another table
body: <p>I have two tables. Appointment and Blacklist. When i blaklist a customer i put his cusId as a foreign key to blacklist table.</p>
  
  <pre><code>Appointment
  ------------
  (AppId,Time,CusId)
  
  
  Blacklist
  -----------
  (CusId,date)
  </code></pre>
  
  <p>Here the CusId is referenced to Customer . What i want is when i search with appointment id in the Appointment table, if the customer relevant to that appointment is in the blacklist table return true else false.</p>
  
  <p>I am new to EF. Please help me to fix this matter.
  Thanks in advance.</p>