在节点 js 函数中使用回调来保留数据库中的值

Question

var mysql = require("mysql");
var thenJade = require('then-jade');
var connection = mysql.createConnection({
host: 'localhost',
user: 'root',
password: '',
database: 'nodejs'
});

exports.players_list = function(req, res) {

var data = {title: "", res: {}};
if (authenticate(req, res)) {

    results_aaa(function(result) {
        console.log(result);
        res.render('players/players', {title: 'Players List', res:   result});
    });

} else {
        req.session.error = 'Please login to continue.';
        res.redirect('/login');
    }
};

function results_aaa(callback) {
    teams(function(res) {
        callback(res)
    });
}

function teams(callback) {
    var response = [];
    var query = connection.query("select * from team", function(err, result, fields) {
         var response = [];
        for (var index in result)
        {
            players(result[index].id, function(results) {                
                response.push(results);
            });
        }
        console.log(response);
        callback(response);        
    });
}

function players(id, callback) {
    query("SELECT * FROM players where team = " + id, function(results) {
        callback(results);
    });
}

function query(sql, callback) {
    connection.query(sql, function(error, results, fields) {
        callback(results);
    });
}

这里我需要根据他们各自的eams来获取球员。但是在 for 循环中，我只得到第一次迭代值。因为对于异步行为，第二次和第三次迭代值是在数据发送到视图之后出现的。请帮忙

[ { id: 2, player_name: 'Virat Kohli', team: '1' },
  { id: 4, player_name: 'A B DeVilliers', team: '1' },
  { id: 6, player_name: 'Chris Gayle', team: '1' } 
    GET /players 200 177ms - 556
[ { id: 7, player_name: 'Ajinkya Rahane', team: '2' },
  { id: 8, player_name: 'Shane Watson', team: '2' },
  { id: 9, player_name: 'Stuart Binny', team: '2' },
  { id: 10, player_name: 'Karun Nair', team: '2' },
  { id: 11, player_name: 'Sanju Samson', team: '2' } ]
[ { id: 1, player_name: 'Virender Sehwag', team: '3' },
  { id: 3, player_name: 'David Miller', team: '3' },
  { id: 5, player_name: 'Shaun Marsh', team: '3' } ]
GET /css/bootstrap.min.css 304 5ms
GET /css/bootstrap.css 304 4ms
GET /css/style.css 304 4ms

如您所见，在第一次迭代后，视图已呈现。如何使用回调等到 forloop 完成执行，以便我将获得所有结果集。

请帮忙

提前致谢

Answer 1

试试这个

    var async = require('async');
var mysql = require("mysql");
var thenJade = require('then-jade');
var connection = mysql.createConnection({
    host: 'localhost',
    user: 'root',
    password: '',
    database: 'nodejs'
});

exports.players_list = function(req, res) {

    var data = {
        title: "",
        res: {}
    };
    if (authenticate(req, res)) {

        results_aaa(function(result) {
            console.log(result);
            res.render('players/players', {
                title: 'Players List',
                res: result
            });
        });

    } else {
        req.session.error = 'Please login to continue.';
        res.redirect('/login');
    }
};

function results_aaa(callback) {
    teams(function(err,res) {
        callback(res);
    });
}

function teams(callback) {
    var response = [];
    var query = connection.query("select * from team", function(err, result, fields) {
        var tasks = [];
        result.forEach(function(team) {
            tasks.push(function(callback1) {
                players(item.id, callback1);
            });
        });
        async.parallel(tasks, function(error, response) {
            callback(null, response);
        });
    });
}

function players(id, callback) {
    query("SELECT * FROM players where team = " + id, function(error,results) {
        callback(error,results);
    });
}

function query(sql, callback) {
    connection.query(sql, function(error, results, fields) {
        callback(error,results);
    });
}

Answer 2

我明白你从哪里来的回电。该问题发生在 'team' 函数内部。当你的 'for' 循环仍然是运行时你的回调被调用。您需要找到一种方法在所有 'player' 查询完成后执行回调。

function teams(callback) {
    var response = [];
    var query = connection.query("select * from team", function(err, result, fields) {
        var response = [];
        for (var index in result)
        {
            players(result[index].id, function(results) {                
                response.push(results);
            });
        }
        console.log(response);
        // The loop will continue the run... (because the queries take longer)
        // the callback is executed BEFORE the loop is finished running
        callback(response);        
    });
}

解决方案一： 查看 promises。查询的结构方式阻止您使用回调来产生预期结果。

方案二：

如果您希望按各自的球队抓取所有球员，您只需要对球员 table 进行一次查询即可获得所需的输出。请查看下面的 query/example（Select 使用 ORDER BY 查询）。

var mysql = require("mysql");
var thenJade = require('then-jade');
var connection = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  password: '',
  database: 'nodejs'
});

var getPlayersByTeam = function(callback) {
  // New query
  var playerQuery = "SELECT * FROM players ORDER BY team ASC"; 

  connection.query(playerQuery, function(err, result, fields) {
    callback(results);
  });

};

var players_list = function(req,res){
  var data = {
    title: "", 
    res: {}
  };

  if (authenticate(req, res)) {
    getPlayersByTeam(function(result){
      res.render('players/players', {title: 'Players List', res: result});
    });
  } else {
    req.session.error = 'Please login to continue.';
    res.redirect('/login');
  }
};

exports.players_list = players_list;

在节点 js 函数中使用回调来保留数据库中的值

Use callbacks in node js function to retain the values from database

javascript

mysql

loops

callback

node.js