项目实训10——有join条件的select

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已于 2022-06-12 09:24:32 修改

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分类专栏：学校信息办数据整理文章标签： java mysql vue.js

于 2022-06-05 17:21:38 首次发布

本文链接：https://blog.youkuaiyun.com/weixin_45873017/article/details/125134008

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1.前端完善

前端增加join关系输入框，并且只有在选择select的时候才显示到页面上。效果如下：
在这里插入图片描述
新增变量代表是否选择select

data（）{
	isSelect：false
}

单选组添加isSelect响应改变方法@change=“changeType”

<el-radio-group v-model="ruleForm.type" @change="changeType">
          <el-radio label="insert"></el-radio>

          <el-radio label="select"></el-radio>
</el-radio-group>

changeType(val){
      if(val === 'select'){
        this.isSelect = true;
      }else {
        this.isSelect = false;
      }
}

join关系输入框通过v-if显示或隐藏

<el-form-item label="join关系" v-if="this.isSelect === true">
        <el-input style="width: 800px" size="large" v-model="ruleForm.relation" ></el-input>
</el-form-item>

2.JSON格式添加字段

添加flag字段表示是否有join条件，添加join字段保存join条件。示例如下：

{"dbname":"student","chartsname":["tijian","HHA"],"metas":{"tijian":{"id":"int","sid":"int","des":"string"},
"HHA":{"SS":"TINYINT"}},"type":"select","key":"这里需填写密钥","flag":true,"join":"hh=hh"}

3.后端处理

public List<List<Object>> selectDataJ(String text){
        UserJson userJson = JSONObject.parseObject(text,UserJson.class);
        List<List<Object>> result = new ArrayList<>();

        List<Object> lm = new ArrayList<>();//生成excel的列名
        String str = "";//select ?
        String cnames = "";//from ?
        String condition = userJson.getJoin();//where？
        for (List<PDetail> pDetails : this.chartnames2) {
            for (PDetail pDetail : pDetails) {
                lm.add(pDetail.getChartname() + "." + pDetail.getMeta());
                str += pDetail.getChartname() + "." + pDetail.getMeta() + ",";
            }
        }

        result.add(lm);

        for (String s : this.chartnames1) {
            cnames += s +",";
        }

        str = str.substring(0,str.length()-1);
        cnames = cnames.substring(0,cnames.length()-1);

        Connection conn = null;
        PreparedStatement psmt = null;
        ResultSet rs = null;
        String jdbcUrl = "jdbc:mysql://localhost:3306/"+this.dbname+"?useSSL=false&serverTimezone=UTC";

        try {
            Class.forName("com.mysql.cj.jdbc.Driver");//————————————————————————————————————————————————————————————————
            //创建连接
            conn = DriverManager.getConnection(jdbcUrl,"root","jiamohan@599");//——————————————————————————
            String sql = "SELECT " + str + " FROM " + cnames + " WHERE " + condition;
            System.out.println(sql);
            psmt = conn.prepareStatement(sql);
            rs = psmt.executeQuery();

            while (rs.next()){
                List<Object> data = new ArrayList<>();
                for (Object o : lm) {
                    data.add(rs.getString(o.toString()));
                }
                result.add(data);
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try {
                rs.close();
                psmt.close();
                conn.close();
            } catch (SQLException e){
                e.printStackTrace();
            }
        }
        return result;
    }