获取特定对象的特定惰性属性

1. JPA EntityGraph

   @Entity
   @Table(name = "foo")
   @NamedEntityGraph(name = "foo.bar",
           attributeNodes = @NamedAttributeNode("bar")
   )
   public class Foo {
   
       @ManyToOne(fetch = FetchType.LAZY)
       private Bar bar;
   
   }
   
   Foo foo = entityManager.find(
       Foo.class,
       id,
       Collections.singletonMap(
           "javax.persistence.fetchgraph",
           entityManager.getEntityGraph("foo.bar")
       )
   );
   

   您可以看到另一个示例和更详细的解释 there .

2. Hibernate profiles

   @Entity
   @Table(name = "foo")
   @FetchProfile(
       name = "foo.bar",
       fetchOverrides = {
           @FetchProfile.FetchOverride(
               entity = Foo.class,
               association = "bar",
               mode = FetchMode.JOIN
           )
       }
   )
   public class Foo {
       @ManyToOne(fetch = FetchType.LAZY)
       private Bar bar;
   }
   
   
   session.enableFetchProfile("foo.bar");
   Foo foo = session.byId(Foo.class).load(id);
   

您可以将JPQL查询用于 FETCH JOIN :

List<Foo> l = em.createQuery(
    "SELECT f FROM Foo f JOIN FETCH f.bar", Foo.class)
    .getResultList();

就这样 Foo Bar 已获取实例。您可以根据需要定制查询。