我制作了包含一些REST服务的Node.js应用程序。这些服务连接到数据库（例如Oracle或DB2)以执行某些查询。
由于我是Node.js编程的初学者，我有一个关于我的案例的问题:什么是访问数据库的正确方式？在应用程序运行时有一个连接引用并在调用REST服务时使用相同的连接实例是否更好？
我发现了一些例子，它们在一个单独的模块中包含数据库连接，并在app中使用该模块，类似于:
db2.js:
var db2 = require('ibm_db');
var db2ConnSettings = "DRIVER={DB2};DATABASE=mydb;HOSTNAME=localhost;UID=db2test;PWD=db2test;PORT=50000;PROTOCOL=TCPIP";
var db2Conn = db2.open(db2ConnSettings, function(err, conn) {
if (err)
return console.log(err);
});
module.exports = db2Conn;
server.js:
var express = require('express');
var app = express();
var db2Connection = require('./db2.js');
app.get('/data', function(req, res) {
console.log(db2Connection );
// make some query
});
当调用此服务时，db2connection是undefined。怎么会？我应该如何从db2.js文件中检索db2连接？
正如@Sirko所说:
var db2 = require('ibm_db');
var db2ConnSettings = "DRIVER={DB2};DATABASE=mydb;HOSTNAME=localhost;UID=db2test;PWD=db2test;PORT=50000;PROTOCOL=TCPIP";
var err, conn;
var callbacks = [];
module.exports = function(callback) {
// db2 module is called
if (err || conn) {
// connection has already been established
// (results of db2.open have been stored)
// callback immediately
callback(err, conn);
}
else {
// connection has not been established
// store the callback for when db connects
callbacks.push(callback);
}
};
db2.open(db2ConnSettings, function(_err, _conn){
// db has connected
err = _err; conn = _conn; // store results
var next_callback;
// array.pop() removed the last item from the array
// and returns it. if no items are left, returns null.
// so this loops through all stored callbacks.
while(next_callback = callbacks.pop()) {
// the removed item is stored in next_callback
next_callback(err, conn); // send connection results to callback
}
// no more items in callbacks to trigger
});
var express = require('express');
var app = express();
var db2Connection = require('./db2.js')(function(err, conn) {
// triggered if the connection has already been established
// or as soon as it HAS been established
app.get('/data', function(req, res) {
console.log(conn);
// ...
});
});
对于带有node-oracledb的Oracle，创建和使用连接池非常简单。您的应用程序只要处理HTTP REST请求，就会从池中获得一个免费连接。查看示例中的webapp.js和webapporations.js。Node-oracledb有一个“连接池队列”（请参阅doc），用于处理连接负载峰值。它还有一个“连接池缓存”（也请参阅文档），这使得访问在不同模块中创建的池变得容易。
