JPA--SpringDataJPA对象导航查询及加载策略

悠悠 2021-08-14 01:12 281阅读 0赞

### 对象导航查询 ###

对象图导航检索方式是根据已经加载的对象，导航到他的关联对象。它利用类与类之间的关系来检索对象。  
例如：我们通过ID查询方式查出一个客户，可以调用Customer类中的getLinkMans()方法来获取该客户的所有联系人。对象导航查询的使用要求是：两个对象之间必须存在关联关系。

### 准备表和数据 ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70]![在这里插入图片描述][20191217234558502.png]

### 实体类 ###

package pers.zhang.entity;
    
    /** * @author zhang * @date 2019/12/15 - 22:10 */
    
    import javax.persistence.*;
    import java.util.HashSet;
    import java.util.Set;
    
    /** * 1.实体类和表的映射关系 * @Entity * @Table * 2.类中属性和表中字段的映射关系 * @Id * @GeneratedValue * @Colum */
    
    @Entity //声明实体类
    @Table(name="cst_customer") //建立实体类和表的映射关系
    public class Customer { 
    
        @Id//声明当前私有属性为主键
        @GeneratedValue(strategy= GenerationType.IDENTITY) //配置主键的生成策略
        @Column(name="cust_id") //指定和表中cust_id字段的映射关系
        private Long custId;
    
        @Column(name="cust_name") //指定和表中cust_name字段的映射关系
        private String custName;
    
        @Column(name="cust_source")//指定和表中cust_source字段的映射关系
        private String custSource;
    
        @Column(name="cust_industry")//指定和表中cust_industry字段的映射关系
        private String custIndustry;
    
        @Column(name="cust_level")//指定和表中cust_level字段的映射关系
        private String custLevel;
    
        @Column(name="cust_address")//指定和表中cust_address字段的映射关系
        private String custAddress;
    
        @Column(name="cust_phone")//指定和表中cust_phone字段的映射关系
        private String custPhone;
    
        //配置客户和联系人之间的关系（一对多）
        /* 1.声明关系： 配置一对多关系：@OneToMany：targetEntity（对方对象的字节码） 2.配置外键（中间表） name:外键字段的名称 referencedColumnName：参照的主表的主键字段名称 在客户实体类上（一的一方）添加了外键的配置，所以对于客户而言，也具备了维护外键的作用 实际情况下，只需要一方维护关系即可 mappedBy表示：放弃外键维护，由对方维护，取值为对方配置关系的属性名称 级联：cascade CascadeType.ALL:所有 MERGE:更新 PERSIST：保存 REMOVE：删除 fetch:配置关联对象的加载方式 EAGER：立即加载 LAZY：延迟加载 */
    // @OneToMany(targetEntity = LinkMan.class)
    // @JoinColumn(name = "lkm_cust_id", referencedColumnName = "cust_id")
        @OneToMany(mappedBy = "customer", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
        private Set<LinkMan> linkMans = new HashSet<>();
    
        public Set<LinkMan> getLinkMans() { 
            return linkMans;
        }
    
        public void setLinkMans(Set<LinkMan> linkMans) { 
            this.linkMans = linkMans;
        }
    
        public Long getCustId() { 
            return custId;
        }
        public void setCustId(Long custId) { 
            this.custId = custId;
        }
        public String getCustName() { 
            return custName;
        }
        public void setCustName(String custName) { 
            this.custName = custName;
        }
        public String getCustSource() { 
            return custSource;
        }
        public void setCustSource(String custSource) { 
            this.custSource = custSource;
        }
        public String getCustIndustry() { 
            return custIndustry;
        }
        public void setCustIndustry(String custIndustry) { 
            this.custIndustry = custIndustry;
        }
        public String getCustLevel() { 
            return custLevel;
        }
        public void setCustLevel(String custLevel) { 
            this.custLevel = custLevel;
        }
        public String getCustAddress() { 
            return custAddress;
        }
        public void setCustAddress(String custAddress) { 
            this.custAddress = custAddress;
        }
        public String getCustPhone() { 
            return custPhone;
        }
        public void setCustPhone(String custPhone) { 
            this.custPhone = custPhone;
        }
    
        @Override
        public String toString() { 
            return "Customer{" +
                    "custId=" + custId +
                    ", custName='" + custName + '\'' +
                    ", custSource='" + custSource + '\'' +
                    ", custIndustry='" + custIndustry + '\'' +
                    ", custLevel='" + custLevel + '\'' +
                    ", custAddress='" + custAddress + '\'' +
                    ", custPhone='" + custPhone + '\'' +
                    '}';
        }
    }

package pers.zhang.entity;
    
    import org.springframework.test.context.ContextConfiguration;
    import sun.awt.SunHints;
    
    import javax.naming.Name;
    import javax.persistence.*;
    
    /** * @author zhang * @date 2019/12/17 - 20:23 */
    @Entity
    @Table(name = "cst_linkman")
    public class LinkMan { 
    
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "lkm_id")
        private Long lkmId;//联系人编号
    
        @Column(name = "lkm_name")
        private String lkmName;//联系人姓名
    
        @Column(name = "lkm_gender")
        private String lkmGender;//联系人性别
    
        @Column(name = "lkm_phone")
        private String lkmPhone;//联系人办公电话
    
        @Column(name = "lkm_mobile")
        private String lkmMobile;//联系人手机
    
        @Column(name = "lkm_email")
        private String lkmEmail;//联系人E-mail
    
        @Column(name = "lkm_position")
        private String lkmPosition;//联系人地址
    
        @Column(name = "lkm_memo")
        private String lkmMemo;//联系人备注
    
        //配置联系人到客户的多对一关系
        /* @ManyToOne：配置多对一关系 targetEntity：对方的实体类额字节码 @JoinColumn：配置外键（中间表） name:外键字段名 referencedColumnName：外键引用的主表主键字段名 */
        @ManyToOne(targetEntity = Customer.class)
        @JoinColumn(name = "lkm_cust_id", referencedColumnName = "cust_id")
        private Customer customer;
    
        public Customer getCustomer() { 
            return customer;
        }
    
        public void setCustomer(Customer customer) { 
            this.customer = customer;
        }
    
        public Long getLkmId() { 
            return lkmId;
        }
    
        public void setLkmId(Long lkmId) { 
            this.lkmId = lkmId;
        }
    
        public String getLkmName() { 
            return lkmName;
        }
    
        public void setLkmName(String lkmName) { 
            this.lkmName = lkmName;
        }
    
        public String getLkmGender() { 
            return lkmGender;
        }
    
        public void setLkmGender(String lkmGender) { 
            this.lkmGender = lkmGender;
        }
    
        public String getLkmPhone() { 
            return lkmPhone;
        }
    
        public void setLkmPhone(String lkmPhone) { 
            this.lkmPhone = lkmPhone;
        }
    
        public String getLkmMobile() { 
            return lkmMobile;
        }
    
        public void setLkmMobile(String lkmMobile) { 
            this.lkmMobile = lkmMobile;
        }
    
        public String getLkmEmail() { 
            return lkmEmail;
        }
    
        public void setLkmEmail(String lkmEmail) { 
            this.lkmEmail = lkmEmail;
        }
    
        public String getLkmPosition() { 
            return lkmPosition;
        }
    
        public void setLkmPosition(String lkmPosition) { 
            this.lkmPosition = lkmPosition;
        }
    
        public String getLkmMemo() { 
            return lkmMemo;
        }
    
        public void setLkmMemo(String lkmMemo) { 
            this.lkmMemo = lkmMemo;
        }
    
    
        @Override
        public String toString() { 
            return "LinkMan{" +
                    "lkmId=" + lkmId +
                    ", lkmName='" + lkmName + '\'' +
                    ", lkmGender='" + lkmGender + '\'' +
                    ", lkmPhone='" + lkmPhone + '\'' +
                    ", lkmMobile='" + lkmMobile + '\'' +
                    ", lkmEmail='" + lkmEmail + '\'' +
                    ", lkmPosition='" + lkmPosition + '\'' +
                    ", lkmMemo='" + lkmMemo + '\'' +
                    '}';
        }
    }

### Dao接口 ###

public interface LinkManDao extends JpaRepository<LinkMan, Long>, JpaSpecificationExecutor<LinkMan> { 
    }

public interface CustomerDao extends JpaRepository<Customer, Long>, JpaSpecificationExecutor<Customer> { 
    }

### 测试类 ###

package pers.zhang;
    
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.test.context.ContextConfiguration;
    import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
    import org.springframework.transaction.annotation.Transactional;
    import pers.zhang.dao.CustomerDao;
    import pers.zhang.dao.LinkManDao;
    import pers.zhang.entity.Customer;
    import pers.zhang.entity.LinkMan;
    
    import java.util.Set;
    
    /** * @author zhang * @date 2019/12/17 - 23:25 */
    @RunWith(SpringJUnit4ClassRunner.class)
    @ContextConfiguration(locations = "classpath:applicationContext.xml")
    public class QueryByObjectTest { 
        @Autowired
        private CustomerDao customerDao;
    
        @Autowired
        private LinkManDao linkManDao;
    
    
        /* 对象导航查询：查询一个对象的时候，通过此对象查询所有关联对象 默认使用的是延迟加载的形式查询的 调用get方法并不会立即发送查询，而是在使用关联对象的时候才会查询 如果不像使用延迟加载： 修改配置：fetch，需要配置到多表映射关系的注解上（OneToMany、ManyToMany、OneToOne） */
        @Test
        @Transactional//解决no session问题
        public void testQuery1(){ 
            Customer customer = customerDao.getOne(10L);
            //对象导航查询，此客户下的所有联系人
            Set<LinkMan> linkMans = customer.getLinkMans();
    
            for(LinkMan l : linkMans)
                System.out.println(l);
    
            /* Hibernate: select customer0_.cust_id as cust_id1_0_0_, customer0_.cust_address as cust_add2_0_0_, customer0_.cust_industry as cust_ind3_0_0_, customer0_.cust_level as cust_lev4_0_0_, customer0_.cust_name as cust_nam5_0_0_, customer0_.cust_phone as cust_pho6_0_0_, customer0_.cust_source as cust_sou7_0_0_ from cst_customer customer0_ where customer0_.cust_id=? Hibernate: select linkmans0_.lkm_cust_id as lkm_cust9_1_0_, linkmans0_.lkm_id as lkm_id1_1_0_, linkmans0_.lkm_id as lkm_id1_1_1_, linkmans0_.lkm_cust_id as lkm_cust9_1_1_, linkmans0_.lkm_email as lkm_emai2_1_1_, linkmans0_.lkm_gender as lkm_gend3_1_1_, linkmans0_.lkm_memo as lkm_memo4_1_1_, linkmans0_.lkm_mobile as lkm_mobi5_1_1_, linkmans0_.lkm_name as lkm_name6_1_1_, linkmans0_.lkm_phone as lkm_phon7_1_1_, linkmans0_.lkm_position as lkm_posi8_1_1_ from cst_linkman linkmans0_ where linkmans0_.lkm_cust_id=? LinkMan{lkmId=3, lkmName='二狗', lkmGender='null', lkmPhone='null', lkmMobile='null', lkmEmail='null', lkmPosition='null', lkmMemo='null'} LinkMan{lkmId=1, lkmName='小李', lkmGender='null', lkmPhone='null', lkmMobile='null', lkmEmail='null', lkmPosition='null', lkmMemo='null'} */
    
        }
    
    
        /* 对象导航查询：查询一个对象的时候，通过此对象查询所有关联对象 */
        @Test
        @Transactional//解决no session问题
        public void testQuery2(){ 
            Customer customer = customerDao.getOne(10L);
            //对象导航查询，此客户下的所有联系人
            Set<LinkMan> linkMans = customer.getLinkMans();
    
            for(LinkMan l : linkMans)
                System.out.println(l);
    
            /* Hibernate: select customer0_.cust_id as cust_id1_0_0_, customer0_.cust_address as cust_add2_0_0_, customer0_.cust_industry as cust_ind3_0_0_, customer0_.cust_level as cust_lev4_0_0_, customer0_.cust_name as cust_nam5_0_0_, customer0_.cust_phone as cust_pho6_0_0_, customer0_.cust_source as cust_sou7_0_0_ from cst_customer customer0_ where customer0_.cust_id=? Hibernate: select linkmans0_.lkm_cust_id as lkm_cust9_1_0_, linkmans0_.lkm_id as lkm_id1_1_0_, linkmans0_.lkm_id as lkm_id1_1_1_, linkmans0_.lkm_cust_id as lkm_cust9_1_1_, linkmans0_.lkm_email as lkm_emai2_1_1_, linkmans0_.lkm_gender as lkm_gend3_1_1_, linkmans0_.lkm_memo as lkm_memo4_1_1_, linkmans0_.lkm_mobile as lkm_mobi5_1_1_, linkmans0_.lkm_name as lkm_name6_1_1_, linkmans0_.lkm_phone as lkm_phon7_1_1_, linkmans0_.lkm_position as lkm_posi8_1_1_ from cst_linkman linkmans0_ where linkmans0_.lkm_cust_id=? LinkMan{lkmId=3, lkmName='二狗', lkmGender='null', lkmPhone='null', lkmMobile='null', lkmEmail='null', lkmPosition='null', lkmMemo='null'} LinkMan{lkmId=1, lkmName='小李', lkmGender='null', lkmPhone='null', lkmMobile='null', lkmEmail='null', lkmPosition='null', lkmMemo='null'} */
    
        }
    
    
        /* 从多的一方查询：从联系人导航查询他所属客户 默认为立即加载 本质为： 从一方查询多方 * 默认：使用延迟加载（****） 从多方查询一方 * 默认：使用立即加载 */
        @Test
        @Transactional//解决no session问题
        public void testQuery3(){ 
            LinkMan linkMan = linkManDao.getOne(2l);
            //对象导航查询所属客户
            Customer customer = linkMan.getCustomer();
            System.out.println(customer);
    
            /* Hibernate: select linkman0_.lkm_id as lkm_id1_1_0_, linkman0_.lkm_cust_id as lkm_cust9_1_0_, linkman0_.lkm_email as lkm_emai2_1_0_, linkman0_.lkm_gender as lkm_gend3_1_0_, linkman0_.lkm_memo as lkm_memo4_1_0_, linkman0_.lkm_mobile as lkm_mobi5_1_0_, linkman0_.lkm_name as lkm_name6_1_0_, linkman0_.lkm_phone as lkm_phon7_1_0_, linkman0_.lkm_position as lkm_posi8_1_0_, customer1_.cust_id as cust_id1_0_1_, customer1_.cust_address as cust_add2_0_1_, customer1_.cust_industry as cust_ind3_0_1_, customer1_.cust_level as cust_lev4_0_1_, customer1_.cust_name as cust_nam5_0_1_, customer1_.cust_phone as cust_pho6_0_1_, customer1_.cust_source as cust_sou7_0_1_ from cst_linkman linkman0_ left outer join cst_customer customer1_ on linkman0_.lkm_cust_id=customer1_.cust_id where linkman0_.lkm_id=? Customer{custId=11, custName='育碧', custSource='null', custIndustry='null', custLevel='null', custAddress='null', custPhone='null'} */
        }
    }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20191217234529138.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NvbGRfX19wbGF5,size_16,color_FFFFFF,t_70
[20191217234558502.png]: /images/20210813/45c4a6f0bf414300b87ec6d4527d75e3.png