MyBatis框架（项目构建笔记）

2023-11-07

MyBatis框架（项目构建笔记）

（一）框架
（二）获取参数
（三）查询
（四）模糊查询、批量删除
（五）resultMap和映射关系
（五）动态SQL

基本功能实现的项目结构，将SqlSessionFactory 使用工具类进行封装。映射文件的名称要与接口的名称一致，在映射文件中实现接口中定义的方法的sql语句。核心配置文件用于配置数据库连接的基本信息和引入映射文件。

项目结构

（一）框架

Maven导入MyBatis配置

<dependencies>
  <!-- Mybatis核心 -->
  <dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.7</version>
  </dependency>

  <!-- junit测试 -->
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
  </dependency>

  <!-- MySQL驱动 -->
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.16</version>
  </dependency>
  
  <!-- log4j日志 -->
  <dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
  </dependency>
  
</dependencies>

Log4j日志配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
    <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
        <param name="Encoding" value="UTF-8" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS}%m (%F:%L) \n" />
        </layout>
    </appender>
    <logger name="java.sql">
        <level value="debug" />
    </logger>
    <logger name="org.apache.ibatis">
        <level value="info" />
    </logger>
    <root>
        <level value="debug" />
        <appender-ref ref="STDOUT" />
    </root>
</log4j:configuration>

Mybatis核心配置文件

<?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>
    <!--设置连接数据库的环境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/test?serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <!--引入映射文件-->
    <mappers>
        <package name="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

创建接口

public interface UserMapper {
    int insertUser();
}

映射文件

<?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="mybatis.mapper.UserMapper">
    <!--int insertUser();-->
    <insert id="insertUser">
        insert into User values('admin','22','admin')
    </insert>
</mapper>

进行测试

@Test
public void InsertTest() throws IOException {
    // 获取核心配置文件的输入流
    InputStream is = Resources.getResourceAsStream("mybatis-config.xml");

	SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
	SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);

	// 获取sql的会话对象sqlsession，是mybatis提供的操作数据库的对象
    SqlSession sqlSession = sqlSessionFactory.openSession();
    
    // 获取接口的代理实现类对象
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    // 调用mapper接口中的方法
    int result = mapper.insertUser();
    System.out.println("结果：" + result);
    // 提交事务
    sqlSession.commit();
    
    sqlSession.close();

}

使用工具类封装，openSession(true)可以自动提交事务

public static SqlSession getSqlSession(){
    SqlSession sqlSession = null;

    try {
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");

        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        sqlSession = sqlSessionFactory.openSession(true);
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
    return sqlSession;
}

select 语句返回值的获取（单条，多条）

@Test
public void testSelect(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.getUsername();
    System.out.println(user);
    sqlSession.close();
}

@Test
public void testSelectAllUser(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    List<User> list = mapper.getAllUser();
    list.forEach(System.out::println);
    sqlSession.close();
}

（二）获取参数

单个参数输入

 <select id="getUsername" resultType="mybatis.pojo.User">
        select * from user where name = #{name}
</select>

@Test
public void testGetUserByName(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.getUsername("w");
    System.out.println(user);
}

多个参数输入

<select id="checkLogin" resultType="mybatis.pojo.User">
    select * from user where name = #{arg0} and password = #{arg1}
</select>

@Test
public void testCheckLogin(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.checkLogin("w","123");
    System.out.println(user);
}

map集合类型的参数输入

<select id="checkLoginByMap" resultType="mybatis.pojo.User">
    select * from user where username = #{username} and password = #{password}
</select>

@Test
public void testCheckLoginByMap(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    Map<String, Object> map = new HashMap<>();
    map.put("username","w");
    map.put("password","123");
    User user = mapper.checkLoginByMap(map);
    System.out.println(user);
}

使用param注解

User checkLoginByParam(@Param("username") String username,@Param("password") String password);

<select id="checkLoginByParam" resultType="mybatis.pojo.User">
    select * from user where username = #{username} and password = #{password}
</select>

@Test
public void testCheckLoginByParam(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.checkLoginByParam("w","123");
    System.out.println(user);
}

（三）查询

创建接口

public interface SelectMapper {
    User1 getUsername(@Param("id") int age);

    List<User1> getAllUser();

    Integer getCount();

    Map<String,Object> getUserByAgeToMap(@Param("id") int age);

    //    List<Map<String,Object>> getAllUserToMap();
    @MapKey("age")
    Map<String,Object> getAllUserToMap();

}

映射文件

<?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="mybatis.mapper.SelectMapper">

    <select id="getUsername" resultType="mybatis.pojo.User1">
        select * from t_user where age = #{id}
    </select>


    <select id="getAllUser" resultType="mybatis.pojo.User1">
        select * from t_user
    </select>

    <select id="getCount" resultType="Integer">
        select count(*) from t_user
    </select>

    <select id="getUserByAgeToMap" resultType="map">
        select * from t_user where age = #{id}
    </select>

    <select id="getAllUserToMap" resultType="map">
        select * from t_user
    </select>

</mapper>

测试类

public class SelectMapperTest {

    @Test
    public void testGetUserByAge(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
        User1 user1 = mapper.getUsername(1);
        System.out.println(user1);
    }

    @Test
    public void testGetAllUser(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
        List<User1> list = mapper.getAllUser();
        list.forEach(System.out::println);
    }

    @Test
    public void testGetCount(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
        Integer count = mapper.getCount();
        System.out.println(count);
    }

    @Test
    public void testGetUserToMap(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
        Map<String,Object> map = mapper.getUserByAgeToMap(1);
        System.out.println(map);
    }

    @Test
    public void testGetAllUserToMap(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
        //        List<Map<String,Object>> list = mapper.getAllUserToMap();
        Map<String,Object> map = mapper.getAllUserToMap();
        System.out.println(map);
    }
}

（四）模糊查询、批量删除

public interface SpecialSQLMapper {

    List<Map<String,Object>> getUserByLike(@Param("mohu") String mohu);

    void DeleteMoreUser(@Param("ids") String ids);

}

<?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="mybatis.mapper.SpecialSQLMapper">

  <select id="getUserByLike" resultType="map">
    select * from t_user where name like '%${mohu}%'
  </select>

  <delete id="DeleteMoreUser" >
    delete from t_user where age in(${ids})
  </delete>


</mapper>

测试类

public class SpecialSQLTest {

    @Test
    public void testSpecialSQL(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        SpecialSQLMapper mapper = sqlSession.getMapper(SpecialSQLMapper.class);
        List<Map<String, Object>> list = mapper.getUserByLike("E");
        System.out.println(list);
    }

    @Test
    public void testDeleteMoreUser(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        SpecialSQLMapper mapper = sqlSession.getMapper(SpecialSQLMapper.class);
        mapper.DeleteMoreUser("1,2");
    }
}

（五）resultMap和映射关系

在MyBatis核心配置中来处理字段（将下划线映射为驼峰）

<settings>
  <setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>

使用resultMap将数据库的字段与实现类匹配

<?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="mapper.EmpMapper">

  <resultMap id="empResultMap" type="pojo.Emp">
    <id column="emp_id" property="empId"></id>
    <result column="emp_name" property="empName"></result>
    <result column="age" property="age"></result>
    <result column="gender" property="gender"></result>
  </resultMap>


  <select id="getEmpByEmpId" resultMap="empResultMap">
    select * from t_emp where emp_id = #{empId}
  </select>

</mapper>

级联方式处理多对一映射

<resultMap id="empAndDeptResultMap" type="pojo.Emp">
  <id column="emp_id" property="empId"></id>
  <result column="emp_name" property="empName"></result>
  <result column="age" property="age"></result>
  <result column="gender" property="gender"></result>
  <result column="dept_id" property="dept.deptId"></result>
  <result column="dept_name" property="dept.deptName"></result>
</resultMap>

<select id="getEmpAndDeptByEmpId" resultMap="empAndDeptResultMap">
  select t_emp.*,t_dept.*
  from t_emp
  left join t_dept on t_emp.dept_id = t_dept.dept_id
  where t_emp.emp_id = ${empId}
</select>

association：处理实体类类型的属性

<resultMap id="empAndDeptResultMap" type="pojo.Emp">
  <id column="emp_id" property="empId"></id>
  <result column="emp_name" property="empName"></result>
  <result column="age" property="age"></result>
  <result column="gender" property="gender"></result>

  <association property="dept" javaType="pojo.Dept">
    <id column="dept_id" property="deptId"></id>
    <result column="dept_name" property="deptName"></result>
  </association>
</resultMap>

<select id="getEmpAndDeptByEmpId" resultMap="empAndDeptResultMap">
  select t_emp.*,t_dept.*
  from t_emp
  left join t_dept on t_emp.dept_id = t_dept.dept_id
  where t_emp.emp_id = ${empId}
</select>

（五）动态SQL

if标签

public interface dynamic {
    List<Emp> getEmpByCondition(Emp emp);
}

<mapper namespace="dynamic">

  <select id="getEmpByCondition" resultType="Emp">
    select * from t_emp where
    <if test="empName != null and empName != ''">
      emp_name = #{empName}
    </if>
    <if test="age != null and age != ''">
      and age = #{age}
    </if>
    <if test="gender != null and gender != ''">
      and gender = #{gender}
    </if>
  </select>

</mapper>

@Test
    public void TestIf(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    dynamic mapper = sqlSession.getMapper(dynamic.class);
    Emp emp = new Emp(null,"张三",20,"男");
    List<Emp> list = mapper.getEmpByCondition(emp);
    list.forEach(System.out::println);
}

where标签

<select id="getEmpByCondition" resultType="Emp">
  select * from t_emp
  <where>
    <if test="empName != null and empName != ''">
      emp_name = #{empName}
    </if>
    <if test="age != null and age != ''">
      and age = #{age}
    </if>
    <if test="gender != null and gender != ''">
      and gender = #{gender}
    </if>
  </where>
</select>

trim标签

<select id="getEmpByCondition" resultType="Emp">
  select * from t_emp
  <trim prefix="where" suffixOverrides="and">
    <if test="empName != null and empName != ''">
      emp_name = #{empName} and
    </if>
    <if test="age != null and age != ''">
      age = #{age} and
    </if>
    <if test="gender != null and gender != ''">
      gender = #{gender}
    </if>
  </trim>
</select>

choose、when、otherwise标签

<select id="getEmpByCondition" resultType="Emp">
  select * from t_emp
  <where>
    <choose>
      <when test="empName != null and empName != ''">
        emp_name = #{empName}
      </when>
      <when test="age != null and age != ''">
        age = #{age}
      </when>
      <when test="gender != null and gender != ''">
        gender = #{gender}
      </when>
      <otherwise>
        emp_id = 2
      </otherwise>
    </choose>
  </where>
</select>

foreach标签，用于批量操作

void insertMoreEmp(@Param("emps") List<Emp> emps);

void deleteMoreEmp(@Param("empIds") Integer[] empIds);

<insert id="insertMoreEmp">
  insert into t_emp values
  <foreach collection="emps" item="emp" separator=",">
    (null,#{emp.empName},#{emp.age},#{emp.gender},null)
  </foreach>
</insert>


<delete id="deleteMoreEmp">
  delete from t_emp where emp_id in
  <foreach collection="empIds" item="empId" separator="," open="(" close=")">
    #{empId}
  </foreach>
</delete>

@Test
    public void TestForeach(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    dynamic mapper = sqlSession.getMapper(dynamic.class);
    Emp emp1 = new Emp(null,"小明1",20,"男");
    Emp emp2 = new Emp(null,"小明1",20,"男");
    Emp emp3 = new Emp(null,"小明1",20,"男");
    List<Emp> list1 = Arrays.asList(emp1, emp2, emp3);
    mapper.insertMoreEmp(list1);
}
@Test
    public void TestForeach2(){
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    dynamic mapper = sqlSession.getMapper(dynamic.class);
    Integer[] empIds = new Integer[]{6,7};
    mapper.deleteMoreEmp(empIds);
}

sql标签

<sql id="empColumns">
  emp_id,emp_name,age,gender,dept_id
</sql>

select <include refid="empColumns"></include> from t_emp

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