SpringData:关联查询

一、查询方式

1、导航式查询

　　使用“对象.属性”   进行查询；对于多的查询， 默认就是延迟加载，添加注解@Transactional

　　在OneToMany 注解中需要添加属性   fetch：值：FetchType.LAZY   延迟加载　　FetchType.ENAGER   及时加载

通过联系人 查询客户；一的查询默认是及时加载，可以配置成延时加载

2、Specification查询

　　需求   查询客户信息  根据联系人的手机号查

　　需要查询  CustomerDao2需要继承JpaSpecificationExecutor接口

二、编写实体类

1、主表实体类关联从表添加属性所需添加的注解　　@OneToMany(mappedBy = "customer",cascade = CascadeType.ALL,fetch = FetchType.LAZY)

2、从表实体类关联主表添加属性所需添加的注解　　@ManyToOne(fetch = FetchType.LAZY)　　@JoinColumn(name="custid",referencedColumnName = "cust_id")

三、编写dao；主表da需要继承JpaRepository和JpaSpecificationExecutor从表dao需要继承JpaRepository

四、测试

package cn.zrf.jpa;

import cn.zrf.jpa.dao.Customer2Dao;
import cn.zrf.jpa.dao.LinkManDao;
import cn.zrf.jpa.entity.Customer2;
import cn.zrf.jpa.entity.LinkMan;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.transaction.annotation.Transactional;

import javax.persistence.criteria.*;
import java.util.Set;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class QueryTest {
    @Autowired
    Customer2Dao customer2Dao;
    @Autowired
    LinkManDao linkManDao;

    @Test
    @Transactional
    public void queryCustomer(){
        Customer2 one = customer2Dao.findOne(1l);
//        System.out.println(one);
        //根据客户查询联系人信息
        Set<LinkMan> set = one.getLinkMans();
        for(LinkMan linkMan:set){
            System.out.println(linkMan);
        }
    }
    //根据联系人查询客户
    @Test
    @Transactional
    public void queryLinkMan(){
        LinkMan one = linkManDao.findOne(3l);
        System.out.println(one);
        Customer2 customer2 = one.getCustomer2();
        System.out.println(customer2);
    }
    //根据手机号查询
    @Test
    @Transactional
    public void questPhone(){
        Customer2 customer2 = customer2Dao.findOne(new Specification<Customer2>() {
            @Override
            public Predicate toPredicate(Root<Customer2> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) {
                //root:关联联系人表
                //参数1、Customer2实体类中关联的属性的名称 参数2、连接方式
                Join<Object, Object> join = root.join("linkMans", JoinType.LEFT);
                //创建查询条件
                Predicate predicate = criteriaBuilder.equal(join.get("lkmPhone"), "1234");
                return predicate;
            }
        });
//        System.out.println(customer2);
        //获得客户信息查询联系人
        Set<LinkMan> linkMans = customer2.getLinkMans();
        for (LinkMan linkMan:linkMans){
            System.out.println(linkMan);
        }

    }
}