Mybatis學習筆記7 - select查詢的相關屬性使用

1、當接口的返回類型是集合List時，resultType要寫集合中元素的類型

示例如下：

接口定義：
package com.mybatis.dao;

import com.mybatis.bean.Employee;

import java.util.*;

public interface EmployeeMapper {
    public List<Employee> getEmpByLastName(String lastName);
}

mapper定義：
<?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.dao.EmployeeMapper">
    <select id="getEmpByLastName" resultType="com.mybatis.bean.Employee">
        select * from tbl_employee where last_name like #{lastName}
    </select>
</mapper>

測試代碼：
package com.mybatis.demo;

import java.io.*;
import java.util.*;

import com.mybatis.bean.Employee;
import com.mybatis.dao.EmployeeMapper;
import org.apache.ibatis.io.*;
import org.apache.ibatis.session.*;
import org.junit.Test;

public class MyTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void testSelect() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            List<Employee> employees = mapper.getEmpByLastName("%e%");
            for (Employee emp : employees) {
                System.out.println(emp);
            }
        } finally {
            openSession.close();
        }
    }
}

2、@MapKey注解：指定使用哪個實體的屬性作為key

示例如下：

接口定義：
package com.mybatis.dao;

import com.mybatis.bean.Employee;
import org.apache.ibatis.annotations.MapKey;

import java.util.*;

public interface EmployeeMapper {
    //返回一條記錄的map；key就是列名，值就是對應的值
    public Map<String, Object> getEmpByIdReturnMap(Integer id);

    //多條記錄封裝一個map：Map<Integer,Employee>:鍵是這條記錄的主鍵，值是記錄封裝后的javaBean
    //@MapKey:告訴mybatis封裝這個map的時候使用哪個屬性作為map的key
    @MapKey("id")
    public Map<Integer, Employee> getEmpReturnMap(String lastName);
}

mapper定義：
<?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.dao.EmployeeMapper">
    <!--public Map<String, Object> getEmpByIdReturnMap(Integer id);-->
    <select id="getEmpByIdReturnMap" resultType="map">
 		select * from tbl_employee where id=#{id}
 	</select>

    <!--public Map<Integer, Employee> getEmpReturnMap(String lastName);  -->
    <select id="getEmpReturnMap" resultType="com.mybatis.bean.Employee">
 		select * from tbl_employee where last_name like #{lastName}
 	</select>
</mapper>

測試代碼：
package com.mybatis.demo;

import java.io.*;
import java.util.*;

import com.mybatis.bean.Employee;
import com.mybatis.dao.EmployeeMapper;
import org.apache.ibatis.io.*;
import org.apache.ibatis.session.*;
import org.junit.Test;

public class MyTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void testSelectOne() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            Map<String, Object> employee = mapper.getEmpByIdReturnMap(1);
            System.out.println(employee);
        } finally {
            openSession.close();
        }
    }

    @Test
    public void testSelectMany() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            Map<Integer, Employee> employee = mapper.getEmpReturnMap("%e%");
            System.out.println(employee);
        } finally {
            openSession.close();
        }
    }
}