mybatis增删改

什么是 MyBatis？

MyBatis 是支持普通 SQL 查询，存储过程和高级映射的优秀持久层框架。 MyBatis 消除了几乎所有的 JDBC 代码和参数的手工设置以及对结果集的检索。MyBatis 可以使用简单的XML 或注解用于配置和原始映射，将接口和 Java 的 POJO（Plain Old Java Objects，普通的Java对象）映射成数据库中的记录。

MyBatis下载：https://github.com/mybatis/mybatis-3/releases

Mybatis实例

对一个User表的CRUD操作：

User表：

-- ----------------------------
-- Table structure for `user`
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `userName` varchar(50) DEFAULT NULL,
  `userAge` int(11) DEFAULT NULL,
  `userAddress` varchar(200) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('1', 'summer', '30', 'shanghai');
INSERT INTO `user` VALUES ('2', 'test2', '22', 'suzhou');
INSERT INTO `user` VALUES ('3', 'test1', '29', 'some place');
INSERT INTO `user` VALUES ('4', 'lu', '28', 'some place');
INSERT INTO `user` VALUES ('5', 'xiaoxun', '27', 'nanjing');

在Src目录下建一个mybatis的xml配置文件Configuration.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!-- mybatis别名定义 -->
    <typeAliases> 
        <typeAlias alias="User" type="com.mybatis.test.User"/> 
    </typeAliases> 

    <environments default="development">
        <environment id="development">
        <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
            <property name="driver" value="com.mysql.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis" />
            <property name="username" value="root"/>
            <property name="password" value="admin"/>
            </dataSource>
        </environment>
    </environments>
    
    <!-- mybatis的mapper文件，每个xml配置文件对应一个接口 -->
    <mappers>
        <mapper resource="com/mybatis/test/User.xml"/>
    </mappers>
</configuration>

定义User mappers的User.xml配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.mybatis.test.IUserOperation">

    <!-- select语句 -->
    <select id="selectUserByID" parameterType="int" resultType="User">
        select * from `user` where user.id = #{id}
    </select>
    
    <!-- 定义的resultMap，可以解决类的属性名和数据库列名不一致的问题-->
    <!-- <resultMap type="User" id="userResultMap">
        <id property="id" column="user_id"  />
        <result property="userName" column="user_userName"  />
        <result property="userAge" column="user_userAge"  />
        <result property="userAddress" column="user_userAddress"  />
    </resultMap> -->
    
    <!-- 返回list的select语句，注意 resultMap的值是指向前面定义好的 -->
    <!-- <select id="selectUsersByName" parameterType="string" resultMap="userResultMap">
        select * from user where user.userName = #{userName}
    </select> -->
    
    <select id="selectUsersByName" parameterType="string" resultType="User">
        select * from user where user.userName = #{userName}
    </select>
    
    <!--执行增加操作的SQL语句。id和parameterType分别与IUserOperation接口中的addUser方法的名字和参数类型一致。
    useGeneratedKeys设置为"true"表明要MyBatis获取由数据库自动生成的主键；keyProperty="id"指定把获取到的主键值注入到User的id属性--> 
    <insert id="addUser" parameterType="User" 
        useGeneratedKeys="true" keyProperty="id"> 
        insert into user(userName,userAge,userAddress)  
             values(#{userName},#{userAge},#{userAddress})  
    </insert>
    
    <update id="updateUser" parameterType="User" >
        update user set userName=#{userName},userAge=#{userAge},userAddress=#{userAddress} where id=#{id}
    </update>
    
    <delete id="deleteUser" parameterType="int">
        delete from user where id=#{id}
    </delete>
    
</mapper>

配置文件实现了接口和SQL语句的映射关系。selectUsersByName采用了2种方式实现，注释掉的也是一种实现，采用resultMap可以把属性和数据库列名映射关系定义好，property为类的属性，column是表的列名，也可以是表列名的别名！

User类的定义：

package com.mybatis.test;

public class User {
    
    private int id;
    private String userName;
    private int userAge;
    private String userAddress;
    
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    
    public String getUserName() {
        return userName;
    }
    
    public void setUserName(String userName) {
        this.userName = userName;
    }
    
    public int getUserAge() {
        return userAge;
    }
    
    public void setUserAge(int userAge) {
        this.userAge = userAge;
    }
    
    public String getUserAddress() {
        return userAddress;
    }
    
    public void setUserAddress(String userAddress) {
        this.userAddress = userAddress;
    }
    
    @Override
    public String toString(){
        return this.userName+" "+this.userAge+" "+this.userAddress;
    }

}

IUserOperaton定义：

package com.mybatis.test;

import java.util.List;

public interface IUserOperation {
    
    public User selectUserByID(int id);
    
    public List<User> selectUsersByName(String userName);
    
    public void addUser(User user);
    
    public void updateUser(User user);
    
    public void deleteUser(int id);
    
}

IUserOperation为操作接口，函数名和mybatis的xml配置文件中的操作id名对应。

测试类Test：

package com.mybatis.test;

import java.io.Reader;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class Test {

    private static SqlSessionFactory sqlSessionFactory;
    private static Reader reader;

    static {
        try {
            reader = Resources.getResourceAsReader("Configuration.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static SqlSessionFactory getSession() {
        return sqlSessionFactory;
    }

    public void getUserByID(int userID) {
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation = session
                    .getMapper(IUserOperation.class);
            User user = userOperation.selectUserByID(userID);
            if (user != null) {
                System.out.println(user.getId() + ":" + user.getUserName()
                        + ":" + user.getUserAddress());
            }

        } finally {
            session.close();
        }
    }

    public void getUserList(String userName) {
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation = session
                    .getMapper(IUserOperation.class);
            List<User> users = userOperation.selectUsersByName(userName);
            for (User user : users) {
                System.out.println(user.getId() + ":" + user.getUserName()
                        + ":" + user.getUserAddress());
            }

        } finally {
            session.close();
        }
    }

    /**
     * 增加后要commit
     */
    public void addUser() {
        User user = new User();
        user.setUserAddress("place");
        user.setUserName("test_add");
        user.setUserAge(30);
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation = session
                    .getMapper(IUserOperation.class);
            userOperation.addUser(user);
            session.commit();
            System.out.println("新增用户ID：" + user.getId());
        } finally {
            session.close();
        }
    }

    /**
     * 修改后要commit
     */
    public void updateUser() {
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation = session
                    .getMapper(IUserOperation.class);
            User user = userOperation.selectUserByID(1);
            if (user != null) {
                user.setUserAddress("A new place");
                userOperation.updateUser(user);
                session.commit();
            }
        } finally {
            session.close();
        }
    }

    /**
     * 删除后要commit.
     * 
     * @param id
     */
    public void deleteUser(int id) {
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation = session
                    .getMapper(IUserOperation.class);
            userOperation.deleteUser(id);
            session.commit();
        } finally {
            session.close();
        }
    }

    public static void main(String[] args) {
        try {
            Test test = new Test();
            // test.getUserByID(1);
            // test.getUserList("test1");
            // test.addUser();
            // test.updateUser();
            // test.deleteUser(6);

        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }

}

 MyBatis Mapper单个参数、多个参数传参区别

1、单个参数

mybatis不会做特殊处理
#{参数名/任意名}：取出参数值。

在接口EmployeeMapper.java中有

public Employee getEmpById(Integer id);

EmployeeMapper.xml中用#{id}取出参数值，因为只有一个，用任意名也可以，如下：

<select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee">
         select * from tbl_employee where id = #{abcde}
</select>

2、多个参数

mybatis会做特殊处理

我们在接口EmployeeMapper.java中新加一个方法：

public Employee getEmpByIdAndLastName(Integer id,String lastName); 

取值方法：用#{id},#{lastName}这种方式取出参数

<select id="getEmpByIdAndLastName" resultType="com.atguigu.mybatis.bean.Employee">
        select * from tbl_employee where id = #{id} and last_name=#{lastName}
    </select>

结果出异常了：

    org.apache.ibatis.binding.BindingException: 
    Parameter 'id' not found. 
    Available parameters are [1, 0, param1, param2]

【命名参数】：明确指定封装参数：

public Employee getEmpByIdAndLastName(@Param("id") Integer id, @Param("lastName") String lastName);

这样就用#{id},#{lastName}这种方式取出参数了：

<select id="getEmpByIdAndLastName" resultType="com.atguigu.mybatis.bean.Employee">
        select * from tbl_employee where id = #{id} and last_name=#{lastName}
</select>