jpa 查询详解

1.1.  一个简单的查询示例

PersonDaoTest.java

package com.morris.test;   import static org.junit.Assert.*;   import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; import javax.persistence.Query;   import org.junit.AfterClass; import org.junit.BeforeClass; import org.junit.Test;   import com.morris.entity.Person;   public class PersonDaoTest {               private static EntityManagerFactory entityManagerFactory;               private static EntityManager entityManager;          @BeforeClass        public static void setUpBeforeClass() throws Exception {                             entityManagerFactory = Persistence.createEntityManagerFactory("jpaDemo");                             entityManager = entityManagerFactory.createEntityManager();                             entityManager.getTransaction().begin();        }          @Test        public void findById() {                 Query query = entityManager.createQuery("select p from Person p where p.id = ?1");                             query.setParameter(1, 1);                             Person person = (Person) query.getSingleResult();                             System.out.println(person);        }               @AfterClass        public static void tearDownAfterClass() throws Exception {               entityManager.getTransaction().commit();               entityManager.close();               entityManagerFactory.close();        } }

1.2.  Query方法详解

1.2.1.  getSingleResult()

返回实体的List集合

1.2.2.  getResultList()

查询结果只有一个

1.2.3.  executeUpdate()

返回执行更新或删除影响的记录数

1.2.4.  setFirstResult

设置返回结果的开始记录数,用于分页查询

1.2.5.  setMaxResults

设置查询的最大记录数,用于分页查询.

1.3.  设置参数

1.3.1.  位置设置

Query query = entityManager.createQuery("select p from Person p where p.id = ?1");               query.setParameter(1, 1);

1.3.2.  命名设置

Query query = entityManager.createQuery("select p from Person p where p.id = :id");               query.setParameter(“id”, 1);

1.4.  Jpql查询

Jpql使用面向对象的方式书写sql语句.

Query query = entityManager.createQuery("select p from Person p where p.id = ?1");               query.setParameter(1, 1);               Person person = (Person) query.getSingleResult();               System.out.println(person);

1.5.  本地查询

本地查询直接使用原生态的sql语句.

Query query = entityManager.createNativeQuery("select name from person where id=:id");               query.setParameter("id", 1);               String name = (String) query.getSingleResult();               System.out.println(name);

 

1.6.  命名查询

命名查询得定义在实体中.

@NamedQuery(name="findById",query="select p from Person p where p.id = :id")

使用:

Query query = entityManager.createNamedQuery("findById");               query.setParameter("id", 1);               Person person =  (Person) query.getSingleResult();               System.out.println(person);

1.7.  本地命名查询

本地命名查询跟命名查询一样定义在实体中,两者的name不能相同,因为调用的方式是一样的.

@NamedNativeQuery(name="findById2",query="select name from person where id=:id")

使用:

Query query = entityManager.createNamedQuery("findById2");               query.setParameter("id", 1);               String name = (String) query.getSingleResult();               System.out.println(name);