MyBatis笔记(注解方式)

注解方式和xml配置方式不同处

不需要配置映射文件
在dao接口中完成注解

核心配置文件

<mappers>
        <mapper class="home.sise.cn.dao.IUserDao"></mapper>
    </mappers>

小注意，如果同时存在规范路径下的映射文件和注解，解析的会混乱

常用增删改操作

select注解

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Select {
  String[] value();
}

在jvm运行时执行，限定作用于方法。

public interface IUserDao {

    /**
     * 查询所有用户
     * @return
     */
    @Select("select * from user")
    List<User> findAll();

    /**
     * 保存用户
     * @param user
     */
    @Insert("insert into user(username,address,sex,birthday)values(#{username},#{address},#{sex},#{birthday})")
    void saveUser(User user);

    /**
     * 更新用户
     * @param user
     */
    @Update("update user set username=#{username},sex=#{sex},birthday=#{birthday},address=#{address} where id=#{id}")
    void updateUser(User user);

    /**
     * 删除用户
     * @param userId
     */
    @Delete("delete from user where id=#{id} ")
    void deleteUser(Integer userId);

    /**
     * 根据id查询用户
     * @param userId
     * @return
     */
    @Select("select * from user  where id=#{id} ")
    User findById(Integer userId);

    /**
     * 根据用户名称模糊查询
     * @param username
     * @return
     */
//    @Select("select * from user where username like #{username} ")
    @Select("select * from user where username like '%${value}%' ")
    List<User> findUserByName(String username);

    /**
     * 查询总用户数量
     * @return
     */
    @Select("select count(*) from user ")
    int findTotalUser();
}

mybatis注解建立实体类属性和数据库表中列的对应关系

Results注解

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Results {
  /**
   * The name of the result map.
   */
  String id() default "";
  Result[] value() default {};
}

result注解

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({})
public @interface Result {
  boolean id() default false;

  String column() default "";

  String property() default "";

  Class<?> javaType() default void.class;

  JdbcType jdbcType() default JdbcType.UNDEFINED;

  Class<? extends TypeHandler> typeHandler() default UnknownTypeHandler.class;

  One one() default @One;

  Many many() default @Many;
}

One注解

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({})
public @interface One {
  String select() default "";

  FetchType fetchType() default FetchType.DEFAULT;

}

Many注解

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({})
public @interface Many {
  String select() default "";

  FetchType fetchType() default FetchType.DEFAULT;

}

FetchType注解(表示加载策略)

public enum FetchType {
  LAZY, EAGER, DEFAULT
}

一个账户所属一个用户： 一对一

public interface IAccountDao {

    /**
     * 查询所有账户，并且获取每个账户所属的用户信息
     * @return
     */
    @Select("select * from account")
    @Results(id="accountMap",value = {
            @Result(id=true,column = "id",property = "id"),
            @Result(column = "uid",property = "uid"),
            @Result(column = "money",property = "money"),
            @Result(property = "user",column = "uid",one=@One(select="home.sise.cn.dao.IUserDao.findById",fetchType= FetchType.EAGER))
    })
    List<Account> findAll();

    /**
     * 根据用户id查询账户信息
     * @param userId
     * @return
     */
    @Select("select * from account where uid = #{userId}")
    List<Account> findAccountByUid(Integer userId);
}

一个用户有多个账户 ： 一对多

@CacheNamespace(blocking = true)
public interface IUserDao {

    /**
     * 查询所有用户
     * @return
     */
    @Select("select * from user")
    @Results(id="userMap",value={
            @Result(id=true,column = "id",property = "userId"),
            @Result(column = "username",property = "userName"),
            @Result(column = "address",property = "userAddress"),
            @Result(column = "sex",property = "userSex"),
            @Result(column = "birthday",property = "userBirthday"),
            @Result(property = "accounts",column = "id",
                    many = @Many(select = "home.sise.cn.dao.IAccountDao.findAccountByUid",
                                fetchType = FetchType.LAZY))
    })
    List<User> findAll();

    /**
     * 根据id查询用户
     * @param userId
     * @return
     */
    @Select("select * from user  where id=#{id} ")
    @ResultMap("userMap")
    User findById(Integer userId);}

开启二级缓存
1.在主配置文件中配置：

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

2.在dao接口上配置注解 ：

@CacheNamespace(blocking = true)
public interface IUserDao {...}