Primary key constraint generated for a "Set" based ElementCollection in Hibernate

Issue

• Defining an @ElementCollection with an @Embeddable type using java.util.Set

  @Embeddable
  public class Task implements Serializable {
      @Column(nullable = false)
      private String name;
      ....
  }
  
  @Entity
  public class Employee ... {
      ...
      @ElementCollection
      @CollectionTable(name = "employee_tasks" ...)
      private Set<Task> tasks = new HashSet<Task>();
      ...
  }
  

• Hibernate generates a primary key constraint on the collection table

  create table employee_tasks (
      Employee_name varchar(255) not null,
      name varchar(255) not null,
      primary key (Employee_name, name)
  )
  

• No primary key constraint is generated when using java.util.List