[英]make NodeJS function synchronus? sends json response before querying database
[英]NodeJs + Postgres synchronus connection to Database to populate variable
我正在使用帶有postgreSQL的nodeJs express 3框架,正在使用以下腳本在DB中查找用戶名並填充變量,以便將其傳遞給視圖。 這是我的腳本:
app.js
var app = express();
app.use(express.bodyParser());
......
function fncCheckUsernameAvailability(vstrUsername){
var pg = require("pg");
var client = new pg.Client({user: 'xxx', password: 'xxxx', database: 'xxx', host: 'example.com'});
var response = "";
client.connect(function(err) {
if(err) {
return console.error('could not connect to postgres', err);
}
client.query("SELECT username FROM users WHERE username ='"+vstrUsername+"'", function(err, result) {
if(err) {
return console.error('error running query', err);
}
if(result.rows[0] == undefined){
//console.log("Username available");
response = "Username available";//Populating The variable here
}else{
//console.log("Username already taken");
response = "Username already taken";//Populating The variable here
}
client.end();
});
});
return response;
}
app.post("/Signup", function(req, res){
var username = req.body.username;
var Response = fncCheckUsernameAvailability(username);
console.log(Response);
}
響應變量始終是“未定義的”,因此如何使該腳本等待數據庫完成檢查以填充“響應”變量?
您不能將返回值放入異步函數中。 相反,您需要使用回調,這是您的代碼可能看起來像的樣子:
function fncCheckUsernameAvailability(vstrUsername, callback) {
client.connect(function(err) {
if (err) {
callback(err, null);
return;
}
client.query("SELECT username FROM users WHERE username ='" + vstrUsername + "'", function (err, result) {
client.end();
if (err) {
callback(err, null);
return;
}
if (result.rows[0] == undefined) callback(null, 'Username available.');
else callback(null, 'Username taken.');
});
});
};
您將使用如下功能:
app.post("/Signup", function(req, res) {
var username = req.body.username;
fncCheckUsernameAvailability(username, function(err, result) {
console.log(result);
});
});
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