Mybatis二

Posted 2021-01-29 xuweiweiwoaini

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1 Mybatis的映射文件

1.1 #和$的区别？

1.1.1 #和$的相同点

都是可以从map中获取值或者pojo对象的值

1.1.2 #和$的不同点

#{}以预编译的形式，将参数设置到sql语句中。
${}取出的值直接拼接在sql语句中，但是可能会有SQL注入问题。

示例：
- EmployeeMapper.java

package com.xuweiwei.mybatis.mapper;

import com.xuweiwei.mybatis.pojo.Employee;
import org.apache.ibatis.annotations.Param;

public interface EmployeeMapper {

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

}

- EmployeeMapper.xml

<?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">
<!--namespace命名空间  指定接口的全类名-->
<mapper namespace="com.xuweiwei.mybatis.mapper.EmployeeMapper">

    <select id="fineEmployeeByIdAndName" resultType="com.xuweiwei.mybatis.pojo.Employee">
        select * from employee where id = ${id} and last_name = #{lastName}
    </select>
</mapper>

- 测试

package com.xuweiwei.mybatis.test;

import com.xuweiwei.mybatis.mapper.EmployeeMapper;
import com.xuweiwei.mybatis.pojo.Employee;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;

public class MybatisTest {

    /**
     * 测试增加
     * @throws IOException
     */
    @Test
    public void test() throws IOException {
        /**
         * 创建SqlSessionFactory对象
         */
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        /**
         * 创建SqlSession
         */
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);

        Employee employee = employeeMapper.fineEmployeeByIdAndName(1, "许威威");

        System.out.println(employee);

        sqlSession.close();
    }

}

View Code

技术分享图片

${}的应用场景：
①分库分表的时候，可以使用${}

select * from ${year}_salary;

②排序

select * from employee order by ${orderColumn} ${order}

③表名

select * from ${tableName}

1.2 select返回

1.2.1 select返回List集合

如果select语句返回的是List集合之类的，在select标签中的resultType只需要写List集合中元素的类型即可。

示例：
- EmployeeMapper.java

package com.xuweiwei.mybatis.mapper;

import com.xuweiwei.mybatis.pojo.Employee;

import java.util.List;

public interface EmployeeMapper {

    List<Employee> findEmployeeListLikeLastName(String lastName);

}

- EmployeeMapper.xml

<?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">
<!--namespace命名空间  指定接口的全类名-->
<mapper namespace="com.xuweiwei.mybatis.mapper.EmployeeMapper">

    <select id="findEmployeeListLikeLastName" resultType="com.xuweiwei.mybatis.pojo.Employee">
        select * from employee where last_name like #{lastName}
    </select>
</mapper>

- 测试

package com.xuweiwei.mybatis.test;

import com.xuweiwei.mybatis.mapper.EmployeeMapper;
import com.xuweiwei.mybatis.pojo.Employee;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MybatisTest {

    /**
     * 测试增加
     * @throws IOException
     */
    @Test
    public void test() throws IOException {
        /**
         * 创建SqlSessionFactory对象
         */
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        /**
         * 创建SqlSession
         */
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
        List<Employee> employeeList = employeeMapper.findEmployeeListLikeLastName("%许%");
        for (Employee employee : employeeList) {
            System.out.println(employee);
        }

        sqlSession.close();
    }
}

View Code

示例：对应的注解写法：

package com.xuweiwei.mybatis.mapper;

import com.xuweiwei.mybatis.pojo.Employee;
import org.apache.ibatis.annotations.ResultType;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface EmployeeMapper {

    @ResultType(Employee.class)
    @Select(" select * from employee where id = #{id} ")
    List<Employee> findEmployeeListLikeLastName(String lastName);

}

1.2.2 select返回Map

map中的key就是列名，value就是对应的值。

示例：
- EmployeeMapper.java

package com.xuweiwei.mybatis.mapper;

import java.util.Map;

public interface EmployeeMapper {

    Map<String,Object> selectEmployeeById(Integer id);

}

- EmployeeMapper.xml

<?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">
<!--namespace命名空间  指定接口的全类名-->
<mapper namespace="com.xuweiwei.mybatis.mapper.EmployeeMapper">

    <select id="selectEmployeeById" resultType="java.util.Map">
        select * from employee where id = #{id}
    </select>

</mapper>

- 测试

package com.xuweiwei.mybatis.test;

import com.xuweiwei.mybatis.mapper.EmployeeMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.Map;

public class MybatisTest {

    /**
     * 测试增加
     *
     * @throws IOException
     */
    @Test
    public void test() throws IOException {
        /**
         * 创建SqlSessionFactory对象
         */
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        /**
         * 创建SqlSession
         */
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
        Map<String, Object> map = employeeMapper.selectEmployeeById(1);

        for (Map.Entry<String, Object> m : map.entrySet()) {
            System.out.println("key:" + m.getKey());
            System.out.println("value:" + m.getValue());
        }

        sqlSession.close();
    }

}

View Code

示例：对应的注解写法

package com.xuweiwei.mybatis.mapper;

import org.apache.ibatis.annotations.ResultType;
import org.apache.ibatis.annotations.Select;

import java.util.Map;

public interface EmployeeMapper {

    @ResultType(Map.class)
    @Select("select * from employee where id = #{id}")
    Map<String,Object> selectEmployeeById(Integer id);

}

Map中的key是主键，value是对应的对象

示例：
- EmployeeMapper.java

package com.xuweiwei.mybatis.mapper;

import com.xuweiwei.mybatis.pojo.Employee;
import org.apache.ibatis.annotations.MapKey;

import java.util.Map;

public interface EmployeeMapper {

    /**
     * 使用注解MapKey告诉Mybatis那个是key
     * @return
     */
    @MapKey("id")
    Map<Integer, Employee> findEmployeeMap();

}

- EmployeeMapper.xml

<?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">
<!--namespace命名空间  指定接口的全类名-->
<mapper namespace="com.xuweiwei.mybatis.mapper.EmployeeMapper">

    <!--这边的resultType实际测试下来既可以是Map中元素Employee也可以是java.util.Map-->
    <select id="findEmployeeMap" resultType="com.xuweiwei.mybatis.pojo.Employee">
        select * from employee
    </select>


</mapper>

- 测试

package com.xuweiwei.mybatis.test;

import com.xuweiwei.mybatis.mapper.EmployeeMapper;
import com.xuweiwei.mybatis.pojo.Employee;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.Map;

public class MybatisTest {

    /**
     * 测试增加
     *
     * @throws IOException
     */
    @Test
    public void test() throws IOException {
        /**
         * 创建SqlSessionFactory对象
         */
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        /**
         * 创建SqlSession
         */
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
        Map<Integer, Employee> employeeMap = employeeMapper.findEmployeeMap();
        System.out.println(employeeMap);

        sqlSession.close();
    }


}

View Code

示例：对应的注解写法

package com.xuweiwei.mybatis.mapper;

import com.xuweiwei.mybatis.pojo.Employee;
import org.apache.ibatis.annotations.MapKey;
import org.apache.ibatis.annotations.ResultType;
import org.apache.ibatis.annotations.Select;

import java.util.Map;

public interface EmployeeMapper {


    @MapKey("id")
    @ResultType(Map.class)
    @Select(" select * from employee ")
    Map<Integer, Employee> findEmployeeMap();

}

1.2.3 select自定义结果集--resultMap

resultMap不能和resultType一起使用。

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