Hibernate笔记6-JPA-注解

一.JPA简介--Java Persistence API。
是SUN公司推出的一套基于ORM的规范。hibernate框架中提供了JPA的实现。JPA通过JDK5.0注解或XML描述对象－关系表的映射关系，并将运行期的实体对象持久化到数据库中。
优势:标准化/容器级特性的支持/简单方便/JPQL查询/面向对象的高级特性

二.基于JPA注解的单表映射
a.导入Hibernate必备的13个jar包;

b.创建Hibernate核心配置文件:hibernate.cfg.xml

  1  <?xml version="1.0" encoding="UTF-8"?>
  2      <!DOCTYPE hibernate-configuration PUBLIC
  3          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
  4          "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
  5      <hibernate-configuration>
  6          <session-factory>
  7                  <!--数据库配置  -->
  8              <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
  9              <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
 10              <property name="hibernate.connection.url">jdbc:mysql:///day58</property>
 11              <property name="hibernate.connection.username">root</property>
 12              <property name="hibernate.connection.password">root</property>
 13                  <!--hibernate基本配置  -->
 14              <property name="hibernate.hbm2ddl.auto">create</property>
 15              <property name="hibernate.show_sql">true</property>
 16              <property name="hibernate.format_sql">true</property>
 17                    <!--配置数据源的提供商 (记得导入c3p0的jar包) -->
 18              <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
 19                  <!--配置事务的隔离级别  -->
 20              <property name="hibernate.connection.isolation">4</property>
 21                  <!--配置与当前线程绑定的session对象  -->
 22               <property name="hibernate.current_session_context_class">thread</property>
 23                  <!--指定映射文件位置 (文件变为class,属性值为类的全限定名) -->
 24              <mapping class="huguangqin.com.cnblogs.entity.Customer"/>
 25          </session-factory>
 26      </hibernate-configuration>

c.使用JPA注解配置实体类

  1  package huguangqin.com.cnblogs.entity;
  2      import java.io.Serializable;
  3      import javax.persistence.Column;
  4      import javax.persistence.Entity;
  5      import javax.persistence.GeneratedValue;
  6      import javax.persistence.GenerationType;
  7      import javax.persistence.Id;
  8      import javax.persistence.Table;
  9 
 10     @Entity // 表示当前类是一个实体类
 11     @Table(name = "cst_customer") // 建立当前实体类与表之间的对应关系
 12     public class Customer implements Serializable {
 13          @Id // 表示当前属性为主键
 14         @GeneratedValue(strategy = GenerationType.IDENTITY) // 指定主键生成策略
 15         @Column(name = "cust_id") // 属性对应的字段名
 16         private Long custId;
 17          @Column(name = "cust_name")
 18          private String custName;
 19          @Column(name = "cust_source")
 20          private String custSource;
 21          @Column(name = "cust_industry")
 22          private String custIndustry;
 23          @Column(name = "cust_level")
 24          private String custLevel;
 25          @Column(name = "cust_address")
 26          private String custAddress;
 27          @Column(name = "cust_phone")
 28          private String custPhone;
 29 
 30         public Long getCustId() {
 31              return custId;
 32          }
 33 
 34         public void setCustId(Long custId) {
 35              this.custId = custId;
 36          }
 37 
 38         public String getCustName() {
 39              return custName;
 40          }
 41 
 42         public void setCustName(String custName) {
 43              this.custName = custName;
 44          }
 45 
 46         public String getCustSource() {
 47              return custSource;
 48          }
 49 
 50         public void setCustSource(String custSource) {
 51              this.custSource = custSource;
 52          }
 53 
 54         public String getCustIndustry() {
 55              return custIndustry;
 56          }
 57 
 58         public void setCustIndustry(String custIndustry) {
 59              this.custIndustry = custIndustry;
 60          }
 61 
 62         public String getCustLevel() {
 63              return custLevel;
 64          }
 65 
 66         public void setCustLevel(String custLevel) {
 67              this.custLevel = custLevel;
 68          }
 69 
 70         public String getCustAddress() {
 71              return custAddress;
 72          }
 73 
 74         public void setCustAddress(String custAddress) {
 75              this.custAddress = custAddress;
 76          }
 77 
 78         public String getCustPhone() {
 79              return custPhone;
 80          }
 81 
 82         public void setCustPhone(String custPhone) {
 83              this.custPhone = custPhone;
 84          }
 85 
 86         // toString
 87          @Override
 88          public String toString() {
 89              return "Customer [custId=" + custId + ", custName=" + custName + ", custSource=" + custSource
 90                      + ", custIndustry=" + custIndustry + ", custLevel=" + custLevel + ", custAddress=" + custAddress
 91                      + ", custPhone=" + custPhone + "]";
 92          }
 93 
 94     }
 95

d.实现保存功能

  1  package huguangqin.com.cnblogs.demo;
  2      import org.hibernate.Session;
  3      import org.hibernate.Transaction;
  4      import org.junit.Test;
  5      import huguangqin.com.cnblogs.entity.Customer;
  6      import huguangqin.com.cnblogs.util.HibernateUtils;
  7 
  8     /**
  9       * 实现保存一个客户的功能
 10      */
 11      public class JPATest {
 12          @Test
 13          public void add() {
 14              // 获取session
 15              Session cs = HibernateUtils.getCurrentSession();
 16              // 开启事务
 17             Transaction tx = cs.beginTransaction();
 18              // 创建对象
 19             Customer c = new Customer();
 20              c.setCustName("大通股份");
 21              // 保存
 22             cs.save(c);
 23              // 提交
 24             tx.commit();
 25          }
 26      }
 27

常用注解说明:
     @Entity
         作用：指定当前类是实体类。写上此注解用于在创建SessionFactory时，加载映射配置。
     @Table
         作用：指定实体类和表之间的对应关系。
         属性：
             name：指定数据库表的名称
     @Id
         作用：指定当前字段是主键。
     @GeneratedValue
         作用：指定主键的生成方式。
         属性：
             strategy ：指定主键生成策略。JPA支持四种生成策略:TABLE,SEQUENCE,IDENTITY,AUTO。
                 IDENTITY：主键由数据库自动生成（主要是自动增长型）;mysql
                 SEQUENCE：根据底层数据库的序列来生成主键，条件是数据库支持序列。 oracle
                 AUTO：主键由程序控制。
                 TABLE：使用一个特定的数据库表格来保存主键。

    @Column
         作用：指定实体类属性和数据库表之间的对应关系
         属性：
             name：指定数据库表的列名称。
             unique：是否唯一
             nullable：是否可以为空
             inserttable：是否可以插入
             updateable：是否可以更新
             columnDefinition: 定义建表时创建此列的DDL
             secondaryTable: 从表名。如果此列不建在主表上（默认建在主表），该属性定义该列所在从表的名字。

三.一对多关系映射
注解说明:
     @OneToMany:
         作用：建立一对多的关系映射
         属性：
             targetEntityClass：指定多方的类的字节码
             mappedBy：指定从表实体类中引用主表对象的名称。
             cascade：指定要使用的级联操作
             fetch：指定是否采用延迟加载
             orphanRemoval：是否使用孤儿删除
     @ManyToOne
         作用：建立多对一的关系
         属性：
              targetEntityClass：指定一的一方实体类字节码
             cascade：指定要使用的级联操作
             fetch：指定是否采用延迟加载
             optional：关联是否可选。如果设置为false，则必须始终存在非空关系。
     @JoinColumn
         作用：用于定义主键字段和外键字段的对应关系。
         属性：
             name：指定外键字段的名称
             referencedColumnName：指定引用主表的主键字段名称
             unique：是否唯一。默认值不唯一
             nullable：是否允许为空。默认值允许。
             insertable：是否允许插入。默认值允许。
             updatable：是否允许更新。默认值允许。
             columnDefinition：列的定义信息。

示例:双向一对多关系
实体类-Customer:

  1  package huguangqin.com.cnblogs.entity;
  2      import java.io.Serializable;
  3      import java.util.HashSet;
  4      import java.util.Set;
  5      import javax.persistence.CascadeType;
  6      import javax.persistence.Column;
  7      import javax.persistence.Entity;
  8      import javax.persistence.GeneratedValue;
  9      import javax.persistence.GenerationType;
 10      import javax.persistence.Id;
 11      import javax.persistence.OneToMany;
 12      import javax.persistence.Table;
 13 
 14     @Entity // 表示当前类是一个实体类
 15     @Table(name = "cst_customer") // 建立当前实体类与表之间的对应关系
 16     public class Customer implements Serializable {
 17          @Id // 表示当前属性为主键
 18         @GeneratedValue(strategy = GenerationType.IDENTITY) // 指定主键生成策略
 19         @Column(name = "cust_id") // 属性对应的字段名
 20         private Long custId;
 21          @Column(name = "cust_name")
 22          private String custName;
 23          @Column(name = "cust_source")
 24          private String custSource;
 25          @Column(name = "cust_industry")
 26          private String custIndustry;
 27          @Column(name = "cust_level")
 28          private String custLevel;
 29          @Column(name = "cust_address")
 30          private String custAddress;
 31          @Column(name = "cust_phone")
 32          private String custPhone;
 33          // 一对多,此处为关键处,mappedBy-放弃外键维护权
 34         @OneToMany(targetEntity = Linkman.class, mappedBy = "customer", cascade = CascadeType.ALL)
 35          private Set<Linkman> linkmans = new HashSet<>();
 36 
 37         public Set<Linkman> getLinkmans() {
 38              return linkmans;
 39          }
 40 
 41         public void setLinkmans(Set<Linkman> linkmans) {
 42              this.linkmans = linkmans;
 43          }
 44 
 45         public Long getCustId() {
 46              return custId;
 47          }
 48 
 49         public void setCustId(Long custId) {
 50              this.custId = custId;
 51          }
 52 
 53         public String getCustName() {
 54              return custName;
 55          }
 56 
 57         public void setCustName(String custName) {
 58              this.custName = custName;
 59          }
 60 
 61         public String getCustSource() {
 62              return custSource;
 63          }
 64 
 65         public void setCustSource(String custSource) {
 66              this.custSource = custSource;
 67          }
 68 
 69         public String getCustIndustry() {
 70              return custIndustry;
 71          }
 72 
 73         public void setCustIndustry(String custIndustry) {
 74              this.custIndustry = custIndustry;
 75          }
 76 
 77         public String getCustLevel() {
 78              return custLevel;
 79          }
 80 
 81         public void setCustLevel(String custLevel) {
 82              this.custLevel = custLevel;
 83          }
 84 
 85         public String getCustAddress() {
 86              return custAddress;
 87          }
 88 
 89         public void setCustAddress(String custAddress) {
 90              this.custAddress = custAddress;
 91          }
 92 
 93         public String getCustPhone() {
 94              return custPhone;
 95          }
 96 
 97         public void setCustPhone(String custPhone) {
 98              this.custPhone = custPhone;
 99          }
100 
101         // toString
102          @Override
103          public String toString() {
104              return "Customer [custId=" + custId + ", custName=" + custName + ", custSource=" + custSource
105                      + ", custIndustry=" + custIndustry + ", custLevel=" + custLevel + ", custAddress=" + custAddress
106                      + ", custPhone=" + custPhone + "]";
107          }
108 
109     }
110

实体类-Linkman

  1 package huguangqin.com.cnblogs.entity;
  2      import java.io.Serializable;
  3      import javax.persistence.Column;
  4      import javax.persistence.Entity;
  5      import javax.persistence.GeneratedValue;
  6      import javax.persistence.GenerationType;
  7      import javax.persistence.Id;
  8      import javax.persistence.JoinColumn;
  9      import javax.persistence.ManyToOne;
 10      import javax.persistence.Table;
 11 
 12     @Entity
 13      @Table(name = "cst_linkman")
 14      public class Linkman implements Serializable {
 15          @Id
 16          @GeneratedValue(strategy = GenerationType.IDENTITY)
 17          @Column(name = "lkm_id")
 18          private Long lkmId;// 联系人编号(主键)
 19          @Column(name = "lkm_name")
 20          private String lkmName;// 姓名
 21         @Column(name = "lkm_gender")
 22          private String lkmGender;// 性别
 23         @Column(name = "lkm_phone")
 24         private String lkmPhone;// 办 公电话
 25         @Column(name = "lkm_mobile")
 26          private String lkmMobile;// 手机
 27         @Column(name = "lkm_email")
 28          private String lkmEmail;// 邮箱
 29         @Column(name = "lkm_position")
 30          private String lkmPosition;// 职位
 31         @Column(name = "lkm_memo")
 32          private String lkmMemo;// 备注
 33         // 多个linkman对应一个customer,此处为关键
 34         @ManyToOne(targetEntity = Customer.class)
 35          @JoinColumn(name = "lkm_cust_id", referencedColumnName = "cust_id") // 指定外键名和参照主键
 36         private Customer customer;
 37 
 38         public Customer getCustomer() {
 39              return customer;
 40          }
 41 
 42         public void setCustomer(Customer customer) {
 43              this.customer = customer;
 44          }
 45 
 46         // getter/setter
 47          public Long getLkmId() {
 48              return lkmId;
 49          }
 50 
 51         public void setLkmId(Long lkmId) {
 52              this.lkmId = lkmId;
 53          }
 54 
 55         public String getLkmName() {
 56              return lkmName;
 57          }
 58 
 59         public void setLkmName(String lkmName) {
 60              this.lkmName = lkmName;
 61          }
 62 
 63         public String getLkmGender() {
 64              return lkmGender;
 65          }
 66 
 67         public void setLkmGender(String lkmGender) {
 68              this.lkmGender = lkmGender;
 69          }
 70 
 71         public String getLkmPhone() {
 72              return lkmPhone;
 73          }
 74 
 75         public void setLkmPhone(String lkmPhone) {
 76              this.lkmPhone = lkmPhone;
 77          }
 78 
 79         public String getLkmMobile() {
 80              return lkmMobile;
 81          }
 82 
 83         public void setLkmMobile(String lkmMobile) {
 84              this.lkmMobile = lkmMobile;
 85          }
 86 
 87         public String getLkmEmail() {
 88             return lkmEmail;
 89          }
 90 
 91         public void setLkmEmail(String lkmEmail) {
 92              this.lkmEmail = lkmEmail;
 93         }
 94 
 95         public String getLkmPosition() {
 96              return lkmPosition;
 97          }
 98 
 99         public void setLkmPosition(String lkmPosition) {
100              this.lkmPosition = lkmPosition;
101          }
102 
103         public String getLkmMemo() {
104              return lkmMemo;
105          }
106 
107         public void setLkmMemo(String lkmMemo) {
108              this.lkmMemo = lkmMemo;
109          }
110 
111         // toString
112          @Override
113          public String toString() {
114              return "Linkman [lkmId=" + lkmId + ", lkmName=" + lkmName + ", lkmGender=" + lkmGender + ", lkmPhone="
115                      + lkmPhone + ", lkmMobile=" + lkmMobile + ", lkmEmail=" + lkmEmail + ", lkmPosition=" + lkmPosition
116                      + ", lkmMemo=" + lkmMemo + "]";
117          }
118 
119     }
120

测试代码:

  1 package huguangqin.com.cnblogs.demo;
  2 
  3     import org.hibernate.Session;
  4      import org.hibernate.Transaction;
  5      import org.junit.Test;
  6 
  7     import huguangqin.com.cnblogs.entity.Customer;
  8      import huguangqin.com.cnblogs.entity.Linkman;
  9      import huguangqin.com.cnblogs.util.HibernateUtils;
 10 
 11     /**
 12       * 一对多,保存一个客户,即能保存对应的多个联系人
 13      */
 14      public class JPATest01 {
 15          @Test
 16          public void add() {
 17              // 获取session
 18              Session cs = HibernateUtils.getCurrentSession();
 19              // 开启事务,并返回事务对象
 20             Transaction tx = cs.beginTransaction();
 21              // 创建对象
 22             Customer c = new Customer();
 23              c.setCustName("百度");
 24              Linkman man = new Linkman();
 25              man.setLkmName("大王");
 26              // 创建关系--双方均需创建关系,否则外键添加不上
 27             c.getLinkmans().add(man);
 28              man.setCustomer(c);
 29              // 保存
 30             cs.save(c);
 31              // 提交事务
 32             tx.commit();
 33          }
 34      }
 35

四.多对多关系映射
注解说明
     @ManyToMany
         作用：用于映射多对多关系
         属性：
             cascade：配置级联操作。
             fetch：配置是否采用延迟加载。
             targetEntity：配置目标的实体类。映射多对多的时候不用写。
     @JoinTable
         作用：针对中间表的配置
         属性：
             nam：配置中间表的名称
             joinColumns：中间表的外键字段关联当前实体类所对应表的主键字段
             inverseJoinColumn：中间表的外键字段关联对方表的主键字段
     @JoinColumn
         作用：用于定义主键字段和外键字段的对应关系。
         属性：
             name：指定外键字段的名称
             referencedColumnName：指定引用主表的主键字段名称
             unique：是否唯一。默认值不唯一
             nullable：是否允许为空。默认值允许。
             insertable：是否允许插入。默认值允许。
             updatable：是否允许更新。默认值允许。
             columnDefinition：列的定义信息。
示例:多对多关系
实体类:-User

  1  package huguangqin.com.cnblogs.entity;
  2      import java.io.Serializable;
  3      import java.util.HashSet;
  4      import java.util.Set;
  5      import javax.persistence.CascadeType;
  6      import javax.persistence.Column;
  7      import javax.persistence.Entity;
  8      import javax.persistence.GeneratedValue;
  9      import javax.persistence.GenerationType;
 10      import javax.persistence.Id;
 11      import javax.persistence.JoinColumn;
 12      import javax.persistence.JoinTable;
 13      import javax.persistence.ManyToMany;
 14      import javax.persistence.Table;
 15 
 16     @Entity
 17      @Table(name = "user")
 18      public class User implements Serializable {
 19 
 20         @Id
 21          @GeneratedValue(strategy = GenerationType.IDENTITY)
 22          @Column(name = "user_id")
 23          private Long userId;
 24 
 25         @Column(name = "user_name")
 26          private String userName;
 27 
 28         @Column
 29          private String address;
 30 
 31         // 对应多个角色
 32         @ManyToMany(targetEntity = Role.class, cascade = CascadeType.ALL)
 33          @JoinTable(name = "role_user",
 34              joinColumns = {@JoinColumn(name = "sys_user_id", referencedColumnName = "user_id") },
 35              inverseJoinColumns = {@JoinColumn(name = "sys_role_id", referencedColumnName = "role_id") })
 36          private Set<Role> roles = new HashSet<>(0);
 37 
 38         // getter/setter
 39          public Long getUserId() {
 40              return userId;
 41          }
 42 
 43         public void setUserId(Long userId) {
 44              this.userId = userId;
 45          }
 46 
 47         public String getUserName() {
 48              return userName;
 49          }
 50 
 51         public void setUserName(String userName) {
 52              this.userName = userName;
 53          }
 54 
 55         public String getAddress() {
 56              return address;
 57          }
 58 
 59         public void setAddress(String address) {
 60              this.address = address;
 61         }
 62 
 63         public Set<Role> getRoles() {
 64              return roles;
 65          }
 66 
 67         public void setRoles(Set<Role> roles) {
 68              this.roles = roles;
 69          }
 70 
 71         // toString
 72          @Override
 73          public String toString() {
 74              return "User [userId=" + userId + ", userName=" + userName + ", address=" + address + ", roles=" + roles + "]";
 75          }
 76 
 77     }
 78

实体类:Role

  1 package huguangqin.com.cnblogs.entity;
  2      import java.io.Serializable;
  3      import java.util.HashSet;
  4      import java.util.Set;
  5      import javax.persistence.Column;
  6      import javax.persistence.Entity;
  7      import javax.persistence.GeneratedValue;
  8      import javax.persistence.GenerationType;
  9      import javax.persistence.Id;
 10      import javax.persistence.ManyToMany;
 11      import javax.persistence.Table;
 12 
 13     @Entity
 14      @Table(name = "role")
 15      public class Role implements Serializable {
 16 
 17         @Id
 18          @GeneratedValue(strategy = GenerationType.IDENTITY)
 19         @Column(name = "role_id")
 20          private Long roleId;
 21 
 22         @Column(name = "role_name")
 23          private String roleName;
 24 
 25         // 对应多个用户
 26         @ManyToMany(mappedBy = "roles") // 放弃维护权,已由对方Role属性维护
 27         private Set<User> users = new HashSet<>(0);
 28 
 29         // getter/setter
 30          public Long getRoleId() {
 31              return roleId;
 32          }
 33 
 34         public void setRoleId(Long roleId) {
 35              this.roleId = roleId;
 36          }
 37 
 38         public String getRoleName() {
 39              return roleName;
 40          }
 41 
 42         public void setRoleName(String roleName) {
 43              this.roleName = roleName;
 44          }
 45 
 46         public Set<User> getUsers() {
 47              return users;
 48          }
 49 
 50         public void setUsers(Set<User> users) {
 51              this.users = users;
 52          }
 53 
 54         // toString
 55          @Override
 56          public String toString() {
 57              return "Role [roleId=" + roleId + ", roleName=" + roleName + ", users=" + users + "]";
 58          }
 59 
 60     }
 61 
 62 测试代码:
 63      package huguangqin.com.cnblogs.demo;
 64     import org.hibernate.Session;
 65      import org.hibernate.Transaction;
 66      import org.junit.Test;
 67      import huguangqin.com.cnblogs.entity.Role;
 68      import huguangqin.com.cnblogs.entity.User;
 69      import huguangqin.com.cnblogs.util.HibernateUtils;
 70 
 71      public class AnotationTest {
 72          @Test
 73          public void test() {
 74              // 获取Session
 75              Session cs = HibernateUtils.getCurrentSession();
 76              // 开启事务
 77             Transaction tx = cs.beginTransaction();
 78              // 构建对象
 79             Role r = new Role();
 80              r.setRoleName("model");
 81             User u = new User();
 82              u.setUserName("Rose");
 83              // 创建关系
 84             r.getUsers().add(u);
 85              u.getRoles().add(r);
 86              // 保存,由于设置了级联操作,只保存一个即可
 87             cs.save(u);
 88              // 提交事务
 89             tx.commit();
 90          }
 91 
 92      }
 93

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原文地址：https://www.cnblogs.com/huguangqin/p/7429942.html