Mybatis 主键配置

墨蓝 2022-06-10 09:59 233阅读 0赞

# 1. 主键回调 #

插入数据时 如果数据库设置了自增长的话 那么无需设置主键会自动由数据库生成 我们插入的时候可以进行配置 使得插入的时候将插入成功生成的主键自动设置到实体类中

例子

实体类User：

package com.hqq.entity;
    
    import java.io.Serializable;
    
    /** * User * Created by heqianqian on 2017/4/27. */
    public class User implements Serializable{ 
    
        private static final long serialVersionUID = 6464657673344930397L;
    
        private Integer id;
        private String name;
        private Integer age;
    
        public User() {
        }
    
        public User(String name, Integer age) {
            this.name = name;
            this.age = age;
        }
    
        public User(Integer id, String name, Integer age) {
            this.id = id;
            this.name = name;
            this.age = age;
        }
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

数据库表users

![这里写图片描述][SouthEast]

这里数据库MySQL 主键设置了自增长

再配置Mapper.xml文件

<insert id="addUser" parameterType="user" keyProperty="id" useGeneratedKeys="true">
               /*keyProperty配置主键对应实体类的属性 useGeneratedKeys是否是自增长*/
            insert into users(name,age) values (#{name},#{age});
        </insert>

这里只需要配置keyProperty为主键对应实体类的属性名称 useGeneratedKeys设置为true

这样插入之后就会将主键回调到实体类中

@Test
        public void testInsert() throws Exception {
            String statement = "com.hqq.entity.User.insertUser";
            User user = new User("hqq", 22);
            int insert = sqlSession.insert(statement, user);
            LOGGER.info("Insert:{}",insert);
            LOGGER.info("User: {}",user.toString());
        }

输出结果：

2017-08-16 14:43:03.941 [main] INFO  TestCRUDByXmlMapper - Insert:1
    2017-08-16 14:43:04.331 [main] INFO  TestCRUDByXmlMapper - User: User{id=12, name='hqq', age=22}

# 2. 自定义主键 #

有时候我们不需要使用数据库的自增长 而是自定义主键  
例如：当表中无数据时 插入时ID设置为1 当存在数据时 插入的ID为当前表中最大ID+2

修改Mapper.xml文件

<insert id="insertUser" parameterType="user">
            <selectKey keyProperty="id" resultType="int" order="BEFORE">
                select if(max(id) is null,1,max(id)+2) as newId from users
            </selectKey>
            insert into users(id,name,age) values (#{id},#{name},#{age});
        </insert>

测试

@Test
        public void testInsert() throws Exception {
            String statement = "com.hqq.entity.User.insertUser";
            User user = new User("Jack", 22);
            int insert = sqlSession.insert(statement, user);
            LOGGER.info("Insert:{}",insert);
            LOGGER.info("User: {}",user.toString());
            insert = sqlSession.insert(statement, new User("Tom",10));
            LOGGER.info("Insert:{}",insert);
            LOGGER.info("User: {}",user.toString());
        }

测试结果

2017-08-16 15:09:52.838 [main] INFO  TestCRUDByXmlMapper - Insert:1
    2017-08-16 15:09:52.841 [main] INFO  TestCRUDByXmlMapper - User: User{id=23, name='Jack', age=22}
    2017-08-16 15:09:52.878 [main] INFO  TestCRUDByXmlMapper - Insert:1
    2017-08-16 15:09:52.879 [main] INFO  TestCRUDByXmlMapper - User: User{id=25, name='Tom', age=10}

--------------------

[SouthEast]: /images/20220610/61da0ced451c4462af535459e58f44c6.png