Mybatis基于接口注解配置SQL映射器(一)

上文已经讲解了基于XML配置的SQL映射器,在XML配置的基础上MyBatis提供了简单的Java注解，使得我们可以不配置XML格式的Mapper文件，也能方便的编写简单的数据库操作代码。

Mybatis之接口注解

映射语句

@Insert

可以使用@Insert注解来定义一个INSERT映射语句：

  @Insert(" insert into sys_user (id, username, password, " +
             "      name, sex, status, org_id, " +
             "      email, idcard, is_admin, " +
             "      sort, mobile, stationid" +
             "      )" +
             "    values (#{id}, #{username}, #{password}," +
             "      #{name}, #{sex}, #{status}, #{orgId}, " +
             "      #{email}, #{idcard}, #{isAdmin}, " +
             "      #{sort}, #{mobile}, #{stationid}" +
             "      )")
     int insertUser(sysUser sysuser);

[自动生成主键]

在上一章中我们讨论过主键列值可以自动生成。我们可以使用@Options注解的userGeneratedKeys 和keyProperty属性让数据库生成AUTO_INCREMENT列的值

    @Insert(" insert into sys_user ( username, password, " +
             "      name, sex, status, org_id, " +
             "      email, idcard, is_admin, " +
             "      sort, mobile, stationid" +
             "      )" +
             "    values ( #{username}, #{password}," +
             "      #{name}, #{sex}, #{status}, #{orgId}, " +
             "      #{email}, #{idcard}, #{isAdmin}, " +
             "      #{sort}, #{mobile}, #{stationid}" +
             "      )")
     @Options(useGeneratedKeys = true, keyProperty = "id")
     int insertUser2(sysUser sysuser);

有些数据库如Oracle并不支持 AUTO_INCREMENT 列，其使用序列（SEQUENCE），或者其他查询（uuid）来生成主键值，如下所示：

 @Insert(" insert into sys_user ( username, password, " +
             "      name, sex, status, org_id, " +
             "      email, idcard, is_admin, " +
             "      sort, mobile, stationid" +
             "      )" +
             "    values ( #{username}, #{password}," +
             "      #{name}, #{sex}, #{status}, #{orgId}, " +
             "      #{email}, #{idcard}, #{isAdmin}, " +
             "      #{sort}, #{mobile}, #{stationid}" +
             "      )")
     @SelectKey(statement=" SELECT replace(uuid(),'-','')  AS id",
             keyProperty="id", resultType=String.class, before=true)
     int insertUser3(sysUser sysuser);

@Update

可以使用@Update注解来定义一个UPDATE映射语句：

 @Update("update sys_user" +
             "    set username = #{username}," +
             "      password = #{password}," +
             "      name = #{name}," +
             "      sex = #{sex}," +
             "      status = #{status}," +
             "      org_id = #{orgId}," +
             "      email = #{email}," +
             "      idcard = #{idcard}," +
             "      is_admin = #{isAdmin}," +
             "      sort = #{sort}," +
             "      mobile = #{mobile}," +
             "      stationid = #{stationid}" +
             "    where id = #{id}")
     int updateUser(sysUser sysuser);

@Delete

可以使用@Delete  注解来定义一个DELETE映射语句：

   @Delete("delete from sys_user WHERE id=#{id}")
     int deleteUser(String id);

@Select

可以使用@ Select注解来定义一个SELECT映射语句：

     @Select("SELECT * FROM sys_user WHERE username = #{username}")
     sysUser findByUsername(@Param("username") String username);

     @Select("SELECT * FROM sys_user WHERE id = #{id}")
     sysUser findById(@Param("id") String id);

结果映射

我们可以将查询结果通过别名或者是@Results注解与JavaBean属性映射起来：

 @Select("SELECT * FROM sys_user WHERE username = #{username}")
     @Results(
             {
                     @Result(id = true, column = "id", property = "id"),
                     @Result(column = "password", property = "password"),
                     @Result(column = "name", property = "name"),
                     @Result(column = "sex", property = "sex")
             })
     sysUser findByUsername(@Param("username") String username);

一对一映射

MyBatis提供了@One注解来使用嵌套select语句（Nested-Select）加载一对一关联查询数据。MyBatis3.2.2版本，并没有对应的注解支持嵌套结果ResultMap。

  @Select("SELECT * FROM sys_user WHERE id = #{id}")
     @Results(
      {
         @Result(id = true,column = "id", property = "id"),
         @Result(column = "password", property = "password"),
         @Result(column = "name", property = "name"),
         @Result(column = "sex", property = "sex"),
         @Result(property = "sysuserinfo", column = "id",
            one = @One(select = "com.goku.mybatis.mapper.sysUserMapper.findsysUserInfo"))
      })
     sysUser findsysUser(@Param("id") String id);

     @Select("select * from sys_user_info where id=#{id}")
     sysUserInfo findsysUserInfo(String id);

一对多映射

MyBatis提供了@Many注解来使用嵌套Select语句加载一对多关联查询。

  @Select("SELECT * FROM sys_org WHERE id = #{id}")
     @Results(
     {
             @Result(id = true,column = "id", property = "id"),
             @Result(column = "version", property = "version"),
             @Result(column = "level", property = "level"),
             @Result(column = "type", property = "type"),
             @Result(property = "sysuser", column = "id",
                     many = @Many(select = "com.goku.mybatis.mapper.sysUserMapper.findByOrgId"))
     })
     sysOrg findsysOrg(@Param("id") String id);

     @Select("SELECT * FROM sys_user WHERE org_id = #{id}")
     sysUser findByOrgId(String id);

动态SQL

有时候我们需要根据输入条件动态地构建SQL语句。MyBatis提供了各种注解如@InsertProvider,@UpdateProvider,@DeleteProvider和@SelectProvider，来帮助构建动态SQL语句，然后让MyBatis执行这些SQL语句。

@SelectProvider

可以使用org.apache.ibatis.jdbc.SQL工具类来构建SQL语句：

 public String findUserByIdSql()
     {
         return new SQL()
         {
             {
                 SELECT("*");
                 FROM("sys_user");
                 WHERE("id=#{id}");
             }
         } .toString();
     }

可以使用@SelectProvider注解来创建一个SELECT映射语句：

    @SelectProvider(type=sysUserDynaSqlProvider.class, method="findUserByIdSql")
     sysUser findUserByIdSql(@Param("id") String id);

SQL工具类会处理以合适的空格前缀和后缀来构造SQL语句。

动态SQL provider方法可以接收以下其中一种参数：

• 无参数
• 和映射器Mapper接口的方法同类型的参数
• java.util.Map

例如 映射器Mapper接口方法只有一个参数，那么可以定义SQLProvider方法，它接受一个与Mapper接口方法相同类型的参数：

  public String findUserByIdSql(final String id)
     {
         return new SQL()
         {
             {
                 SELECT("*");
                 FROM("sys_user");
                 WHERE("id='"+id+"'");
             }
         } .toString();
     }

如果映射器Mapper接口有多个输入参数，我们可以使用参数类型为java.util.Map的方法作为SQLprovider方法。MyBatis提供的多值映射参数，使用的是#{param}语法。

 public String findUserByIdSql2(Map<String, Object> map)
     {
         return new SQL()
         {
             {
                 SELECT("*");
                 FROM("sys_user");
                 WHERE("id=#{param1} and username=#{param2}");
             }
         } .toString();
     }

     @SelectProvider(type=sysUserDynaSqlProvider.class, method="findUserByIdSql2")
     sysUser findUserByIdSql2(String id, String name);

SQL工具类也提供了其他的方法来表示JOINS，ORDER_BY，GROUP_BY等等。

例如 使用LEFT_OUTER_JOIN的例子：

  public String findUserinfoByIdSql()
     {
         return new SQL()
         {
             {
                 SELECT("u.id, username, password, name, sex, status, org_id, email, idcard, is_admin, sort," +
                         "        mobile,address, post_code, height, weight, birthday, blood, culture, finish_school_date," +
                         "        folk, government, homepage, householder, marriage, msn, nativity_address, qq, speciality," +
                         "        description, version");
                 FROM("sys_user u");
                 LEFT_OUTER_JOIN("sys_user_info t on u.id=t.id");
                 WHERE("u.id=#{id}");
             }
         } .toString();
     }

     @SelectProvider(type=sysUserDynaSqlProvider.class, method="findUserinfoByIdSql")
     List<Map<String, String>> findUserinfoByIdSql(@Param("id") String id);

@InsertProvider

可以使用@InsertProvider注解创建动态的INSERT语句:

     public String insertUser(final sysUser sys_user)
     {
         return new SQL()
         {
             {
                 INSERT_INTO("sys_user");
                 if (sys_user.getId()!=null)
                 {
                     VALUES("id", "#{id}");
                 }
                 if (sys_user.getName() != null)
                 {
                     VALUES("name", "#{name}");
                 }
             }
         } .toString();
     }

  @InsertProvider(type = sysUserDynaSqlProvider.class, method = "insertUser")
     int insertUser4(sysUser sysuser);

@UpdateProvider

可以通过@UpdateProvider注解创建动态的UPDATE语句：

     public String updateUser(final sysUser sys_user)
     {
         return new SQL()
         {
             {
                 UPDATE("sys_user");
                 if (sys_user.getName() != null)
                 {
                     SET("name = #{name}");
                 }
                 WHERE("id = #{id}");
             }
         } .toString();
     }

     @InsertProvider(type = sysUserDynaSqlProvider.class, method = "updateUser")
     int updateUser2(sysUser sysuser);

@DeleteProvider

可以使用@DeleteProvider注解创建动态的DELETE语句：

     public String deleteUser()
     {
         return new SQL()
         {
             {
                 DELETE_FROM("sys_user");
                 WHERE("id = #{id}");
             }
         } .toString();
     }

     @DeleteProvider(type = sysUserDynaSqlProvider.class, method = "deleteUser")
     int deleteUser2(@Param("id") String id);

GITHUB

github : https://github.com/nbfujx/learn-java-demo/tree/master/Goku.MybatisDemo.Annotation