Error in JPA mapping - Fetch Comments

Question

I'm trying to fetch comments using the ticket field as a foreign key but I'm getting the following errors:

Caused by: Exception [EclipseLink-6078] (Eclipse Persistence Services - 2.0.1.v20100213-r6600): org.eclipse.persistence.exceptions.QueryException
Exception Description: The class of the argument for the object comparison is incorrect.         

Expression: [
Base com.test.forum.model.Comment] 
Mapping: [org.eclipse.persistence.mappings.OneToOneMapping[ticket]] 
Argument: [751]

This is the code i'm using in my javabean: - Hide quoted text -

  @JoinColumn(name = "ticket", referencedColumnName = "id")
  @ManyToOne(optional = false)
  private Ticket ticket;


    public List<Comment> findComment(int id) {
      Query q = em.createQuery("SELECT c FROM Comment c WHERE c.ticket = 751");
      return q.getResultList();
    }

Thanks

Answer 1

A Ticket object obviously cannot be equal to 751. Its ID can. So WHERE c.ticket.id = 751

(For the future: I doubt you will be hardcoding the ID, so use a named parameter)