Mybatis使用

mybatis-config.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>
  <environments default="development">
    <environment id="development"> <!-- 设置环境 -->
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${驱动类（含包名）}"/>
        <property name="url" value="${数据库连接URL}"/>
        <property name="username" value="${用户名}"/>
        <property name="password" value="${密码}"/>
      </dataSource>
    </environment>
  </environments>
</configuration>

Util

一般只需要创建一次，所以创建一个工具类

public class MybatisUtil {

    //在类加载时就进行创建
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(new FileInputStream("mybatis-config.xml"));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

    /**
     * 获取一个新的会话
     * @param autoCommit 是否开启自动提交（跟JDBC是一样的，如果不自动提交，则会变成事务操作）
     * @return SqlSession对象
     */
    public static SqlSession getSession(boolean autoCommit){
        return sqlSessionFactory.openSession(autoCommit);
    }
}

在其他函数里直接使用

try (SqlSession session = MybatisUtil.getSession(true)) {
    session.selectOne("id", argu);
}

Mapper

原始方法

1. 在mybatis-config.xml中添加

<mappers>
    <mapper url="file:mappers/TestMapper.xml"/>
    <!--    这里用的是url，也可以使用其他类型，我们会在后面讲解    -->
</mappers>

2. 定义TestMapper.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="com.test.mapper.TestMapper"> <!-- 命名空间指明mapper接口名 -->
    <select id="selectStudent" resultType="com.test.entity.Student">
        <!-- id：函数名；resultType：返回类型 -->
        select * from student
    </select>
    <select id="selectOneStudent" resultType="com.test.entity.Student">
        <!-- id：函数名；resultType：返回类型 -->
        select * from student where sid = #{sid}
    </select>
</mapper>

使用

public static void main(String[] args) throws FileNotFoundException {
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(new FileInputStream("mybatis-config.xml")); // config 文件路径
    try (SqlSession sqlSession = sqlSessionFactory.openSession(true)){
        List<Student> student = sqlSession.selectList("selectStudent"); // xml id
        Student stu3 = sqlSession.selectOne("selectOneStudent", 3); // 传参
        student.forEach(System.out::println);
    }
}

接口方法

1. 在mybatis-config.xml中添加

<mappers>
    <mapper resource="com/test/mapper/TestMapper.xml"/>
</mappers>

2. 定义TestMapper.xml和接口TestMapper.java

public interface TestMapper {
    List<Student> selectStudent();
}

使用

public static void main(String[] args) {
    try (SqlSession sqlSession = MybatisUtil.getSession(true)){
        TestMapper testMapper = sqlSession.getMapper(TestMapper.class);
        List<Student> student = testMapper.selectStudent(); // 已经定义好了类型
        student.forEach(System.out::println);
    }
}

注解方法

1. 在mybatis-config.xml中添加

<mappers>
    <mapper class="com.test.mapper.TestMapper"/> 
    // 单个java class
</mappers>

或者

<mappers>
    <mapper package="com.test.mapper"/> 
    // 整个包
</mappers>

使用

public interface TestMapper {
    @Results({
        @Result(id = true, column = "id", property = "sid", 
                one = @One(select = "method")),
    })
    @Select("select * from student") // 注解
    List<Student> selectStudent();

    @Select("select * from student where sid = #{s}, bid = #{book.bid}")
    Student selectStudentBySid(@Param("s") int sid, @Param("book") Book book) // 标明变量

    Type method();
}

动态SQL

if

<if test="argu == value">
    // your sql query.
</if>