如何存储查询Mysql

Question

我将使用不同的Id值获取我的数据库两次。但我需要在某处保存这两个查询，然后将它们发送到res.render。我已经尝试保存在数组中，但它返回undefined。

app.post('/searchInventory', urlencodedParser, function(req, res){
        con.query("SELECT id FROM products WHERE name LIKE '%" + req.body.keyword + "%'", function(err, result){
            data = [];
            for(var a = 0; a < result.length; a++){
                console.log(a);
                con.query("SELECT products.id AS id, products.name AS name, products.price AS price, SUM(enter.quantity) AS quantity FROM products JOIN enter ON products.id = enter.id_prod WHERE enter.id_prod = "+mysql.escape(result[a].id)+";", function(err, results, fields){
                // I need to store the query from here
                data =+ results
                });
            }
            console.log(data); //Undefined
            res.render('inventory', {results: results});
        });
    })

Answer 1

问题是围绕异步数据库查询需要注意。首先要做的是使其简单易读，这就是创建查询承诺。

function dbQueryPromise(query) {
  return new Promise((resolve, reject) => {
    con.query(query, (err, results) => {
      if(err) return reject(err);
      resolve(results);
    })
  })
}

现在您可以使用此承诺来处理您所需的行为：

dbQueryPromise("SELECT id FROM products WHERE name LIKE '%" + req.body.keyword + "%'")
  .then(results => {
   const promiseArray = results.map(result => {
     return dbQueryPromise("SELECT products.id AS id, products.name AS name, products.price AS price, SUM(enter.quantity) AS quantity FROM products JOIN enter ON products.id = enter.id_prod WHERE enter.id_prod = "+mysql.escape(result.id)+";")
   })
   Promise.all(promiseArray).then(allResults => { res.render('inventory', { results: allResults})})
})

Answer 2

您可以使用子查询来查询产品而不是查询两次。

con.query("SELECT products.id AS id, products.name AS name, products.price AS price, SUM(enter.quantity) AS quantity FROM products JOIN enter ON products.id = enter.id_prod WHERE enter.id_prod IN ( SELECT id FROM products WHERE name LIKE '%?%') ", req.body.keyword, function( error, result){
    console.log(result)
})

另外，data + = result不会堆叠数组。您可以使用Array.prototype.concat组合两个数组。

例：

data = data.concat(result) 

要么

data = [].concat(data, result)