@namedqueries_在@NamedQueries中枚举@NamedQuery

@namedqueries

介绍

如果您是使用JPA的Java开发人员，则很可能在实体上声明了一个或多个@NamedQuery对象。

要在类上声明@NamedQuery ，必须在类中简单地用查询名称及其JPQL进行注释，例如：

@Entity
@NamedQuery(name = "findAllProjects",query = "select p from Project p order by p.id")
public class Project

但是，如果我们想声明多个@NamedQuery批注，注释，我们用类@NamedQueries批注，然后包含集合@NamedQuery注释，如下所示：

@Entity
@NamedQueries({ @NamedQuery(name = "findAllProjects",query = "select p from Project p order by p.id"),@NamedQuery(name = "findById",query = "select p from Project p where p.id=:id")
})
public class Project

枚举@NamedQuery批注

创建具有多个@NamedQuery批注的实体后，如何检查类中存在哪些批注？

幸运的是，使用反射，枚举类中的注释并找到有关它们的详细信息非常简单，如下面的代码所示。

NamedQueries annotation = Project.class.getAnnotation(NamedQueries.class);
for (Annotation annot : annotation.value()) {System.out.println(annot.toString());for (Method method : annot.annotationType().getDeclaredMethods()) {if (method.getName().equalsIgnoreCase("name") ||method.getName().equalsIgnoreCase("query")) {try {String result = method.getName() + " : " + method.invoke(annot,  null).toString();System.out.println(result);} catch (IllegalAccessException | IllegalArgumentException| InvocationTargetException e) {// Oops - something has gone wrong.break;}}}
}

运行上面的代码将产生以下输出：

@javax.persistence.NamedQuery(lockMode=NONE, hints=[], name=findAllProjects, query=select p from Project p order by p.id)
name : findAllProjects
query : select p from Project p order by p.id@javax.persistence.NamedQuery(lockMode=NONE, hints=[], name=findById, query=select p from Project p where p.id=:id)
name : findById
query : select p from Project p where p.id=:id