Question

我正在使用Node JS向数据库发出请求。碰巧我正在做一个SELECT语句，之后我需要它的结果来执行INSERT。

 var index = 1;
    async.whilst(
        function() { return index < 10; },
        function(callback) {
            index++;
            let line = csv_json[index][0].split(';');
            let block = csv_json[index];
            read_account(line);
            callback(null, index);
        },
        function(err, n) {
            if (err) throw err;
        }
    );


function read_account(csv, index) {
    if (index == csv_json.length) return;

    let line = csv_json[index][0].split(';');
    let block = csv_json[index];
    var account = line[0];

    waterfall([
        function(callback) {
            connection.query('SELECT id FROM account WHERE account_number = ' + account,
                function(error, results, fields) {
                    if (error)
                        throw error;
                    console.log(results);
                    callback(null, results);

                });

        },
        function(results, callback) {

            if (results == null || typeof results == undefined || results.length == 0) {
                console.log("ENTREI");
                connection.query('INSERT INTO account (account_number) VALUES (' + account + ')',
                    function(err, results, fields) {

                        callback(err, "1 account inserted!")
                        if (err)
                            throw err;
                    });
            }
            //else  callback(null,"record already in db")

        },
    ], function(err, success) {
        if (err) throw err;
        //console.log(success);
    });
};

由于Node是异步的，当我调用read-account（）时，我从INSERT得到的结果总是来自数据库的第一个状态。如何使这个进程同步？

谢谢

Answer 1

您可以在Select函数的回调中编写第二个函数。

function read_account(csv, index) {
    if (index == csv_json.length) return;

    let line = csv_json[index][0].split(';');
    let block = csv_json[index];
    var account = line[0];
    connection.query('SELECT id FROM account WHERE account_number = ' + account,
        function(error, results, fields) {
            if (error)
                throw error;
            console.log(results);

            if (results == null || typeof results == undefined || results.length == 0) {
                console.log("ENTREI");
                connection.query('INSERT INTO account (account_number) VALUES (' + account + ')',
                    function(err, results, fields) {

                        callback(err, "1 account inserted!")
                        if (err)
                            throw err;
                    });
            }

        });
};

您可以考虑为select和insert编写两个不同的函数：

function select(callback){
 connection.query('SELECT id FROM account WHERE account_number = ' + account, function(error, results, fields) {
      if (error) {
        return callback(error);
      } else {
        return callback(null, results, fields);
      }
  });
}

function insert(results, fileds, callback){
  connection.query('INSERT INTO account (account_number) VALUES (' + account + ')',
      function(err, results, fields) {
          if (err){
            return callback(err);
          } else {
            return callback(null, "1 account inserted!")
          }
      });
}

function read_account(csv, index, callback) {
    if (index == csv_json.length) return;
    let line = csv_json[index][0].split(';');
    let block = csv_json[index];
    var account = line[0];

    select(function(null, results, fields){
      if(err){
        return callback(err);
      } else {
        insert(results, fileds, callback);
      }
    });
  }

在Node JS中同步循环

1 个答案: