项目——通过自动回复机器人学Mybatis(六)

一对多关系的配置

如果每次输入某个指令，机器人回复的都是同一内容那就太尴尬了

原先数据库只有一张表Message，因为出现了一对多关系，现将其拆分成command表和command_content表

command表{id,name,description}

command_content表{id,content,command_id}

CommandContent.xml:

<mapper namespace="CommandContent">

  <resultMap type="com.csdn.bean.CommandContent" id="commandcontent">
    <id column="id" jdbcType="INTEGER" property="id"/>
    <result column="content" jdbcType="VARCHAR" property="content"/>
    <result column="command_id" jdbcType="INTEGER" property="command_id"/>
  </resultMap>

</mapper>

Command.xml:

<mapper namespace="Command">

  <resultMap type="com.csdn.bean.Command" id="command">
    <id column="c_id" jdbcType="INTEGER" property="id"/>
    <result column="name" jdbcType="VARCHAR" property="name"/>
    <result column="description" jdbcType="VARCHAR" property="description"/>
    <collection property="contentList" resultMap="CommandContent.commandcontent"/>
  </resultMap>

  <select id="queryCommandList" parameterType="com.csdn.bean.Command" resultMap="command">
    select a.id c_id,a.name,a.description,b.content,b.id,b.command_id 
    from command a left join command_content b
    on a.id=b.command_id
    <where>
    	<if test="name != null and !"".equals(name.trim())">
	    	and a.name=#{name}
	    </if>
	    <if test="description != null and !"".equals(description.trim())">
	    	and a.description like '%' #{description} '%'
	    </if>
    </where>
  </select>
 
</mapper>

CommandDao.java:

public class CommandDao {
	
	public List<Command> queryCommandList(String name,String description){
		DBAccess dbAccess = new DBAccess();
		SqlSession sqlSession=null;
		List<Command> selectList =new ArrayList<Command>();
		try {
			sqlSession=dbAccess.getSqlSession();
			Command comm = new Command();
			comm.setName(name);
			comm.setDescription(description);
			//通过sqlSession执行SQL语句
			selectList = sqlSession.selectList("Command.queryCommandList",comm);
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			if(sqlSession!=null){
				sqlSession.close();
			}
			
		}
		return selectList;
	}
}

QueryService.java:

将原先代码中的MessageDao替换成CommandDao

public class QueryService {
	
	public List<Command> queryCommandList(String name,String description){
		CommandDao commandDao=new CommandDao();
		return commandDao.queryCommandList(name,description);
	}
	
	public String queryByCommand(String command){
		CommandDao commandDao=new CommandDao();
		List<Command> commandList;
		if(Iconst.HELP.equals(command)){
			commandList=commandDao.queryCommandList(null, null);
			StringBuilder result = new StringBuilder();
			for(int i=0;i<commandList.size();i++){
				if(i!=0){
					result.append("<br/>");
				}
				result.append("回复["+commandList.get(i).getName()+"]可以查看"+commandList.get(i).getDescription());
			}
			return result.toString();
		}
		commandList = commandDao.queryCommandList(command, null);
		if(commandList.size()>0){
			List<CommandContent> contentList = commandList.get(0).getContentList();
			return contentList.get(new Random().nextInt(contentList.size())).getContent();
		}
		return Iconst.NO_MATCHING_CONTENT;
	}
}

contentList.get(new Random().nextInt(contentList.size())).getContent();实现了随机获取command对应的content，这样就不会每次返回统一内容

AutoReplyServlet:

protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
		req.setCharacterEncoding("UTF-8");
		res.setContentType("text/html;charset=utf-8");
		PrintWriter out = res.getWriter();
		QueryService queryservice = new QueryService();
		out.write(queryservice.queryByCommand(req.getParameter("content")));
		out.flush();
		out.close();
	}

实现效果:

Mapper映射文件常用标签:

容易混淆的概念:

我觉得就介绍一下#{}和${}就好，这个用的比较多

#{}有预编译效果，会被替换成?；而${}不会，它会直接在解析sql时直接用传进来的参数值替代，使用时别忘了用单引号括起来  '${}'

使用${}的场景一般是 order by  '${xxxx}'，总不能order by  ?  把

常见问题:

如果你的Command表的主键是自增的，在做新增一个command功能时你会碰到一个问题，新增时你不知道command主键

<insert id="insert" useGeneratedKeys="true" keyProperty="id" parameterType="com.csdn.bean.Command">
  	insert into command(name,description) values(#{name},#{description})
  </insert>

useGeneratedKeys="true"   使用自增主键

 keyProperty="id"                 将获得的自增主键值传给command对象的id属性

一开始传入的command对象中id为空，但是在sqlSession执行到此sql时command对象中id就有值了