When using Express+NodeJS+MongoDB+MongoSkin to quickly build a web application, reading data failed.
On the premise of opening the database connection and creating a piece of data, I did this:
1: data connection in app.js
// Database
var mongo = require('mongoskin');
var db = mongo.db("mongodb://localhost:27017/learn3", {native_parser:true});
2: Connect the database to the http request
// Make our db accessible to our routerapp.use(function(req,res,next){
req.db = db;
next();
});
The code for posting app.js is as follows:
var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
// Database
var mongo = require('mongoskin');
var db = mongo.db("mongodb://localhost:27017/learn3", {native_parser:true});
var routes = require('./routes/index');
var users = require('./routes/users');
var app = express();
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');
// uncomment after placing your favicon in /public
//app.use(favicon(__dirname + '/public/favicon.ico'));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use('/', routes);
app.use('/users', users);
// Make our db accessible to our router
app.use(function(req,res,next){
req.db = db;
next();
});
// catch 404 and forward to error handler
app.use(function(req, res, next) {
var err = new Error('Not Found');
err.status = 404;
next(err);
});
// error handlers
// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
app.use(function(err, req, res, next) {
res.status(err.status || 500);
res.render('error', {
message: err.message,
error: err
});
});
}
// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
res.status(err.status || 500);
res.render('error', {
message: err.message,
error: {}
});
});
module.exports = app;
3: at. \routes\users.js edit as follows:
var express = require('express');
var router = express.Router();
/**
* GET userlist.
*/
router.get('/userlist', function(req, res) {
var db = req.db;
db.collection('userlist').find().toArray(function(err, items) {
res.json(items);
})
// res.send('respond with a resource');
});
module.exports = router;
4: open the service, after npm start, visithttp://localhost:3000/users/userlist, found that the report was wrong.
The error message is: cannotcallmethod ‘collection’ of undefined.
Looking at the Internet, I found this usage is also possible. Please help me look at it.
The reason is found:
// Make our db accessible to our router app.use(function(req,res,next){ req.db = db; next(); }); app.use('/', routes); app.use('/users', users);
Above, I put the value of req.db below. I think it was not instantiated to db when calling req.db, so I reported an error when calling collection later. As for the deeper reasons, I still need to explore. When I wrote it, I felt that the upper and lower positions might not matter much. If there is a friend who can answer this question, please look at it. Thank you very much.