技術標籤：MyBatis學習筆記mybatis

多個對映檔案

• 在 Configuration XML 裡可以配置多個對映檔案

在mybatis-config.xml裡面可以配置多個mapper，可以減少混亂。

<?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>
  <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/af_example?useUnicode=true&amp;characterEncoding=UTF-8"/>
        <property name="username" value="root"/>
        <property name="password" value="a1b2c3"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="mybatis-mapper-student.xml"/>
	<mapper resource="mybatis-mapper-teacher.xml"/>
  </mappers>
</configuration>
 

mybatis-mapper-student.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">
  
<mapper namespace="af.student">
  <select id="get" resultType="my.Student">
    select * from student where id = #{id}
  </select>  
</mapper>
 

mybatis-mapper-teacher.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">
  
<mapper namespace="af.teacher">
  <select id="list" resultType="hashmap">  
    select * from teacher order by id ASC
  </select>
</mapper>
 

註解方式的Mapper

• 除了xml方式的mapper，Mapper也可以用Java程式碼的方式來定義
• 步驟 ：

1.定義一個介面，對應於 Mapper

新增一些方法

添加註解，定義SQL和引數

方法的引數，方法的返回值型別

2.在mybatis-config.xml裡註冊

3.在程式碼裡呼叫

• 註解方式寫的mapper優點：簡潔一些，引數型別和返回值可以自動提示
• 註解方式寫的mapper缺點：不適用於複雜的SQL（比如太長的SQL，要換行書寫）

1.新增介面類mapper StudentMapper.java

package my;

import org.apache.ibatis.annotations.Select;

import my.Student;

public interface StudentMapper
{
	 @Select("SELECT * FROM student WHERE id = #{id}")
	 Student getStudent(int id);
}

我們來與xml形式的mapper對比一下

<?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="af.student">
  <select id="getStu" resultType="my.Student">
    select * from student where id = #{id}
  </select>  
</mapper>

介面類裡面的getStudent對應xml裡面的id，引數id對應sql裡面的引數id，Student對應xml裡面的resultType。

再新增另一個mapper TeacherMapper.java

package my;

import java.util.List;
import java.util.Map;

import org.apache.ibatis.annotations.Select;

public interface TeacherMapper
{
	 @Select("SELECT * FROM teacher ORDER BY ID ASC ")
	 List<Map> getList();
}

2.在mybatis-config.xml裡註冊mapper

<?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>
  <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/af_example?useUnicode=true&amp;characterEncoding=UTF-8"/>
        <property name="username" value="root"/>
        <property name="password" value="a1b2c3"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
	<mapper class="my.StudentMapper"/>
	<mapper class="my.TeacherMapper"/>
  </mappers>
</configuration>

3.測試

package my;

import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;

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
{
	public static void main(String[] args) throws Exception
	{
		// 建立 SqlSessionFactory
		String resource = "mybatis-config.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

		// 以註解方式定義的 Mapper
		try (SqlSession session = sqlSessionFactory.openSession()) {
			StudentMapper mapper = session.getMapper(StudentMapper.class);
			Student stu = mapper.getStudent(20190001);
			if(stu != null)
				System.out.println("找到學生記錄");				
		}

		try (SqlSession session = sqlSessionFactory.openSession()) {
			TeacherMapper mapper = session.getMapper(TeacherMapper.class);
			List<Map> rows = mapper.getList();
			if(rows != null)
				System.out.println("找到教師記錄: " + rows.size());				
		}
		
		System.out.println("Exit");
	}

}

4.結果