1.1 基本使用
1.1.1 常用注解
| 注解 | 描述 |
|---|---|
| @Insert | 实现新增 |
| @Update | 实现更新 |
| @Delete | 实现删除 |
| @Select | 实现查询 |
| @Result | 实现结果集封装 |
| @Results | 可以与 @Result 一起使用，封装多个结果集 |
| @One | 实现一对一结果集封装 |
| @Many | 实现一对多结果集封装 |
1.1.2 MyBatis 增删改查
实体类
public class Student {
private Long sId;
private String sName;
private Long sAge;
private String sSex;
// set and get
}
DAO
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);
}
配置文件
<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>
<!-- 指定接口所在的包 -->
<package name="com.software.mybatis.dao"/>
<!-- 指定接口 -->
<mapper class="com.software.mybatis.dao.StudentDao"/>
</mappers>
测试
public class MybatisDemo {
private StudentDao studentDao;
@Before
public void before() throws IOException {
// 加载核心配置文件
InputStream resourceAsStream = Resources.getResourceAsStream("mybatis.xml");
// 获得 sqlSession 工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
// 获得 sqlSession 对象
SqlSession sqlSession = sqlSessionFactory.openSession();
// 获取 mapper
studentDao = sqlSession.getMapper(StudentDao.class);
}
@Test
public void TestA() throws IOException {
List<Student> studentList = studentDao.findAll();
System.out.println(studentList);
}
}
我们可以看到，明明结果已经查询出来了，为什么打印出来却是空的。这个是因为属性名和列名不一致造成的，类似于我们这种 sId s_id 可以打开驼峰之自动转换。如果二者之间没有任何联系就需要使用 @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 复杂映射
1.2.1 注解详解
| 注解 | 说明 |
|---|---|
| @Results | 代替的是标签该注解中可以使用单个@Result注解，也可以使用@Result集合 使用格式：@Results（{@Result（），@Result（）}）或@Results（@Result（）） |
| @Result | 代替了标签和标签 @Result中属性介绍： column：数据库的列名 property：需要装配的属性名 one：需要使用的@One 注解（@Result（one=@One）（））） many：需要使用的@Many 注解（@Result（many=@many）（））） |
| @One(一对一) | 代替了标签，是多表查询的关键，在注解中用来指定子查询返回单一对象。 @One注解属性介绍： select：指定用来多表查询的sqlmapper使用格式：@Result（column=""，property="".one=@One（select="）） |
| @Many(一对多) | 代替了标签，是是多表查询的关键，在注解中用来指定子查询返回对象集合。 使用格式：@Result（property="".column="，many=@Many（select="）） |
1.2.2 一对一
实体类
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"),
// 类似于先查询出 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 一对多
实体类
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"),
// 类似于先查询 class 然后使用 c_id 查询 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 多对多
实体类
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"),
// 类似于先查询 student 然后连接查询 course 和 s_c 表条件为 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();
}
