Mybatis 注解

1.1 基本使用

1.1.1 常用注解

1.1.2 MyBatis 增刪改查

? 物體類

public class Student {
    private Long sId;
    private String sName;
    private Long sAge;
    private String sSex;
	
	// set and get

}

? DAO

/**
 * Created with IntelliJ IDEA.
 *
 * @author Demo_Null
 * @date 2020/9/9
 * @description Mybatis 注解
 */
public interface StudentDao {

    @Select("select * from student")
    public List<Student> findAll();

    @Select("select * from where s_id = #{id} ")
    public Student findOne(Long id);

    @Insert("insert into student values (#{sId}, #{sName}), #{sAge}, #{sSex}")
    public int insert(Student student);

    @Update("update from student set s_id = #{sId}, s_name = #{sName}, s_age = #{sAge}, s_sex = #{sSex}")
    public int update(Student student);
    
    @Delete("delete from student where s_id = #{id} ")
    public int delete(Long id);
}

? 組態檔

<typeAliases>
    <package name="com.software.mybatis.entity"/>
</typeAliases>

<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://localhost:3306/db"/>
            <property name="username" value="root"/>
            <property name="password" value="root"/>
        </dataSource>
    </environment>
</environments>

<mappers>
	<!-- 指定介面所在的包 -->
    <package name="com.software.mybatis.dao"/>
	<!-- 指定介面 -->
    <mapper class="com.software.mybatis.dao.StudentDao"/>
</mappers>

? 測驗

/**
 * Created with IntelliJ IDEA.
 *
 * @author Demo_Null
 * @date 2020/9/9
 * @description
 */
public class MybatisDemo {

    private StudentDao studentDao;

    @Before
    public void before() throws IOException {
        // 加載核心組態檔
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis.xml");
        // 獲得 sqlSession 工廠物件
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        // 獲得 sqlSession 物件
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 獲取 mapper
        studentDao = sqlSession.getMapper(StudentDao.class);
    }

    @Test
    public void TestA() throws IOException {
        List<Student> studentList = studentDao.findAll();

        System.out.println(studentList);
    }

}

??我們可以看到，明明結果已經查詢出來了，為什么列印出來卻是空的，這個是因為屬性名和列名不一致造成的，類似于我們這種 sId ? s_id 可以打開駝峰之自動轉換，如果二者之間沒有任何聯系就需要使用 @Results 一一映射，

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

@Select("select * from student")
@Results(value = {
                @Result(property = "sId", column = "s_id"),
                @Result(property = "sName", column = "s_name"),
                @Result(property = "sAge", column = "s_age"),
                @Result(property = "sSex", column = "s_sex")
})
public List<Student> findAll();

1.2 復雜映射

1.2.1 注解詳解

1.2.2 一對一

? 物體類

public class Student {
    private Long sId;
    private String sName;
    private Long sAge;
    private String sSex;
    private Class class;

    // set and get
}

public class Class {
    private Long cId;
    private String cName;
    private String cAddr;

    // set and get
}

? DAO

public interface ClassDao {
    @Select("select * from class where c_id = #{id} ")
    public Class findById(Long id);
}

public interface StudentDao {

    @Select("select * from student")
    @Results({
            @Result(property = "sId", column = "s_id"),
            @Result(property = "sName", column = "s_name"),
            @Result(property = "sAge", column = "s_age"),
            @Result(property = "sSex", column = "s_sex"),
            // 類似于先查詢出 student 然后拿 c_id 再去查 class
            @Result(property = "class", column = "c_id", javaType = Class.class,
            		one = @One(select = "com.software.mybatis.dao.ClassDao.findById"))
    })
    public List<Student> findAll();
}

1.2.3 一對多

? 物體類

public class Student {
    private Long sId;
    private String sName;
    private Long sAge;
    private String sSex;
    private Long cId;

    // set and get
}

public class Class {
    private Long cId;
    private String cName;
    private String cAddr;
    private List<Student> students;

    // set and get
}

? DAO

public interface StudentDao {
    @Select("select * from where c_id = #{id} ")
    public List<Student> findByCid(Long id);
}

public interface ClassDao {
    @Select("select * from class")
    @Results({
            @Result(property = "cId", column = "c_id"),
            @Result(property = "cName", column = "c_name"),
            @Result(property = "cAddr", column = "c_addr"),
            // 類似于先查詢 class 然后使用 c_id 查詢 student
            @Result(property = "students", column = "c_id", javaType = List.class,
                    many = @Many(select = "com.software.mybatis.dao.StudentDao.findByCid")),
    })
    public List<Class> findAll();
}

1.2.4 多對多

? 物體類

public class Course {
    private Integer cId;
    private String cName;
    private List<Student> students;
    
    // set and get
}

public class Student {
    private Integer sId;
    private String sName;
    private Long sAge;
    private String sSex;
    private List<Course> courses;
        
    // set and get
}

? DAO

public interface CourseDao {
    @Select("select * from course c, s_c sc where c.c_id = sc.c_id and sc.s_id = #{id} ")
    public List<Course> findBySid(Long id);
}

public interface StudentDao {
    @Select("select * from student")
    @Results({
            @Result(property = "sId", column = "s_id"),
            @Result(property = "sName", column = "s_name"),
            @Result(property = "sAge", column = "s_age"),
            @Result(property = "sSex", column = "s_sex"),
            // 類似于先查詢 student 然后連接查詢 course 和 s_c 表條件為 c.c_id = sc.c_id and s_id = sc.s_id
            @Result(property = "Courses", column = "s_id", javaType = List.class,
            		many = @Many(select = "com.software.mybatis.dao.CoursesDao.findBySid"))
    })
    public List<Student> findAll();
}