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();
}
}
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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);
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1.3.2. 命名设置
Query query = entityManager.createQuery("select p from Person p where p.id = :id");
query.setParameter(“id”, 1);
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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);
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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");
"id", 1);
String name = (String) query.getSingleResult();
System.out.println(name);
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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")
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使用:
Query query = entityManager.createNamedQuery("findById");
"id", 1);
Person person = (Person) query.getSingleResult();
System.out.println(person);
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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")
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使用:
Query query = entityManager.createNamedQuery("findById2");
query.setParameter("id", 1);
query.getSingleResult();
System.out.println(name);
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