Expensive multi-table JOIN query when association is initialized in Hibernate

Issue

• Associating several distinct subclasses in a JOINED inheritance hierarchy with another entity (e.g. Owner)
• The targetEntity in each @OneToMany association was added to resolve the join column defined in the superclass.
• Restrictions were applied to resolve discrepancies between the classes since re-using the foreign key

• Each of the associations are unidirectional

  @MappedSuperclass
  public class Task ... {
      ...
      @Column(name = "OWNERID")
      public long getOwnerId() {
          ...
      }
      ...
  }
  
  @Entity
  @Inheritance(strategy = InheritanceType.JOINED)
  public class ProjectTask extends Task ... {
      ...
  }
  
  @Entity
  @Inheritance(strategy = InheritanceType.JOINED)
  public class LearningTask extends Task ... {
      ...
  }
  
  @Entity
  @Inheritance(strategy = InheritanceType.JOINED)
  public class ReviewTask extends Task ... {
      ...
  }
  
  @Entity
  public class Owner {
      ...
  
      @OneToMany(targetEntity = Task.class, ...)
      @JoinColumn(name = "OWNERID")
      @Where(...)
      @Filter(...)
      public Set<ProjectTask> getProjectTasks() {
          ...
      }
  
      @OneToMany(targetEntity = Task.class, ...)
      @JoinColumn(name = "OWNERID")
      @Where(...)
      @Filter(...)
      public Set<LearningTask> getLearningTasks() {
          ...
      }
  
      @OneToMany(targetEntity = Task.class, ...)
      @JoinColumn(name = "OWNERID")
      @Where(...)
      @Filter(...)
      public Set<ReviewTask> getReviewTasks() {
          ...
      }
  }
  

• At runtime, when any one of the associations is navigated/traversed (explicitly or implicitly) a join query including each of the sibling classes is observed in the log

  ... DEBUG [org.hibernate.SQL] ... select ...
      from Owner ...
      left outer join Task ...
      left outer join ProjectTask ...
      left outer join LearningTask ...
      left outer join ResearchTask ...
      ...
      where ...