java - 抽象类中的 Hibernate NamedQuery

Question

我有 20 个继承自 AbstractEntity 的类，它们都需要具有相同的 NamedQueries，作为示例，我们举一个简单的例子:

@NamedQuery(name = Bootle.FIND_BY_ID, query = //
        "SELECT entity FROM " + Bootle.ENTITY_NAME + " entity " + 
        "LEFT OUTER JOIN FETCH entity.value val " + 
        "..." +
        "WHERE entity.id = :pIds AND entity.relationable = :pBoolean")

我希望我可以将这些查询移至 AbstractEntity，但是我无法确定 hibernate 的 EntityName。理想的解决方案是以某种方式拥有它:

@NamedQuery(name = BaseDAO.FIND_BY_ID, query = //
            "SELECT entity FROM " + AbstractEntity.ENTITY_NAME + " entity " + 
            "LEFT OUTER JOIN FETCH entity.value val " + 
            "..." +
            "WHERE entity.id = :pIds AND entity.relationable = :pBoolean")

但是上面的例子不起作用。当我查询此方法时，Hibernate 本身可以给出正确的实体名称吗？

当前查询调用的示例:

getEntityManager().createNamedQuery(BaseDAO.FIND_BY_ID)
                .setParameter("pId", 201L)
                .setParameter("pBoolean", false);

Answer 1

来自文档。 https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.query.spel-expressions

To avoid stating the actual entity name in the query string of a @Query annotation, you can use the #{#entityName} variable.

The entityName can be customized by using the @Entity annotation. Customizations in orm.xml are not supported for the SpEL expressions. Of course, you could have just used User in the query declaration directly, but that would require you to change the query as well. The reference to #entityName picks up potential future remappings of the User class to a different entity name (for example, by using @Entity(name = "MyUser").

Another use case for the #{#entityName} expression in a query string is if you want to define a generic repository interface with specialized repository interfaces for a concrete domain type. To not repeat the definition of custom query methods on the concrete interfaces, you can use the entity name expression in the query string of the @Query annotation in the generic repository interface.

示例

@MappedSuperclass
public abstract class AbstractMappedType {
  …
  String attribute
}

@Entity
public class ConcreteType extends AbstractMappedType { … }

@NoRepositoryBean
public interface MappedTypeRepository<T extends AbstractMappedType>
  extends Repository<T, Long> {

  @Query("select t from #{#entityName} t where t.attribute = ?1")
  List<T> findAllByAttribute(String attribute);
}

public interface ConcreteRepository
  extends MappedTypeRepository<ConcreteType> { … }