【发布时间】：2017-02-14 05:01:04
【问题描述】：
我是 Nodejs 的新手，并且还来自过程语言背景，所以我需要了解我的代码的执行流程。我有一个关于 Nodejs 程序流程的一般性问题。这是场景：
代码结构：
Appnamefolder
...standard node folders(.idea,css,fonts,etc)
...model
....database.js (connect to db and execute db queries)
...public
...routes
....users.js (GET and POST procedures....calls db queries via module.export)
...views
...app.js
...other js files
问题与数据库有关。由于数据库连接不在 app.js 文件中，而是在模型文件夹中的 .js 文件中，在什么时候建立了数据库连接？每次进行数据库查询时都会建立连接吗？
我希望发生的是，数据库连接只进行一次并保持连接，直到应用程序终止。我尝试将数据库连接放在 app.js 中，但是当我尝试数据库查询时出现错误，所以我必须将数据库连接放在与数据库查询相同的文件中......不知何故这对我来说似乎是错误的。谁能解释节点如何处理此流程？....将不胜感激。
编辑：这是代码示例
app.js
var express = require('express');
var path=require('path');
var bodyParser = require('body-parser');
var cookieParser=require('cookie-parser');
var expressSession=require('express-session');
var expejs = require('ejs');
var expressValidator = require('express-validator');
var flash = require('connect-flash');
var expressSession = require('express-session');
var expressLayouts=require("express-ejs-layouts") // add this requirement
var passport = require('passport');
var LocalStrategy = require('passport-local').Strategy;
var crypto = require("crypto");
var loaddealerTable=require('./loaddealerTable');
//var neo4j = require('neo4j-driver').v1;
// var neo4jdb = neo4j.driver("bolt://localhost:7474", neo4j.auth.basic("neo4j", "password"),
// {
// trust: "TRUST_ON_FIRST_USE",
// encrypted:true
// });
//***************Notifications Permission*******
var routes = require('./routes/index');
var users = require('./routes/users');
var csocket=require('./socketconnections');
var app=express();
var server=require('http').createServer(app);
sockets = require('./socketserver');
//rpaMessageWaiting = require('./getRPAmessages');
//var io=require('socket.io').listen(server);
// View Engine
app.set('views', path.join(__dirname,'views'));
app.set('view options', { layout:'layout.ejs' });
app.set('view engine','ejs');
//bodyParsers middleware
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.use(cookieParser());
app.use(expressLayouts);
//set up public folder
app.use(express.static(path.join(__dirname, '/public')));
// set express session with secret
app.use(expressSession({ secret: process.env.SESSION_SECRET || 'secret',
resave: true,
saveUninitialized: true
}));
// Passport initialization
app.use(passport.initialize());
app.use(passport.session());
//Express Validitor...validate inputs..taken from github middleware options
app.use(expressValidator({
errorFormatter: function(param, msg, value) {
var namespace = param.split('.')
, root = namespace.shift()
, formParam = root;
while(namespace.length) {
formParam += '[' + namespace.shift() + ']';
}
return {
param : formParam,
msg : msg,
value : value
};
}
}));
// connect flash middleware
app.use(flash());
// set global variables for flash messages
app.use(function (req, res, next)
{
res.locals.success_msg = req.flash('success_msg');
res.locals.error_msg = req.flash('error_msg');
res.locals.error = req.flash('error');
res.locals.user = req.user || null;
next();
});
// Middelware for route files
app.use('/', routes);
app.use('/users', users); //need to check routing
sockets.startSocketServer(server);
//load dealer table
console.log("load dealer table");
**loaddealerTable(); //First call on the DB**
//============socket io listening=======================
app.set('port',(process.env.PORT|| 3000));
server.listen(app.get('port'), function()
{
console.log('Server started on port '+app.get('port'));
// console.log('Server started on port .....');
// app.get('/index',function (req,res) {
// // body...
// res.render(__dirname+'/index');
});
loaddealertable.js
var loaddealerTable=function()
{
var memorytbl=require('./memorytables');
var User = require('./model/user');
var getHashKey=require('./gethashkey');
const hashMax=1000;
console.log("call get dealers from DB");
User.getallDealers(function(err,dealerFound,result)
{
if (dealerFound)
{
//
for (i=0; i< result.records.length; i++)
{
memorytbl.Dealer.email =result.records[i].get(0).properties.email;
memorytbl.Dealer.name =result.records[i].get(0).properties.name;
memorytbl.Dealer.telephone =result.records[i].get(0).properties.storenumber;
memorytbl.Dealer.creditcard =result.records[i].get(0).properties.creditcard;
memorytbl.Dealer.delivery =result.records[i].get(0).properties.delivery;
memorytbl.Dealer.location =result.records[i].get(0).properties.location;
memorytbl.Dealer.rating =result.records[i].get(0).properties.rating;
var hashIndex = getHashKey(memorytbl.Dealer.email ,hashMax);
memorytbl.DealersQ[hashIndex]=memorytbl.Dealer;
} //end of for i
} //end of if....
else
{
console.log("No dealers found....table is empty");
}
}) //end of loaddealers table db call
} //end of load dealers table function
module.exports=loaddealerTable;
user.js
var express = require('express');
var bcrypt = require('bcryptjs');
var router = express.Router();
var neo4j = require('neo4j-driver').v1;
var driver = neo4j.driver("bolt://localhost", neo4j.auth.basic("neo4j", "password"));
var session = driver.session();
//============Load Memory Tables=========================
router.getallDealers=function(callback) {
session
.run ("MATCH (user:Dealer) RETURN user")
.then (function(result)
{
if ( !result.records[0])
{
console.log("No Dealers Found");
session.close();
if (typeof callback==="function") {
return callback(null,false,result);
}
} // end of if not found
else
{
console.log("Dealer Found");
session.close();
if (typeof callback === "function")
{
return callback(null, true, result);
}
}
// or close session here??
}) //end of .then block
.catch(function(err)
{
console.log("DB call error: "+err);
}); //.then block
} //end of get dealers
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标签： node.js