node.js应用程序-如何通过include连接到mongodb和“共享”连接？

Question

Background Information

I'm attempting my first node.js API/application. As a learning exercise, I'm trying to create some test cases initially delete all records in a table, insert 3 specific records, and then query for those 3 records.

Code

Here's the code I have cobbled together:

http://pastebin.com/duQQu3fm

Problem

As you can see from the code, I'm trying to put the database connection logic in a dbSession.js file and pass it around.

I am able to start up the http server by doing the following:

dev@devbox:~/nimble_node$ sudo nodejs src/backend/index.js 
Server started and listening on port: 8080
Database connection successful

However, when I try to run my jasmine tests, it fails with the following error:

F

Failures:

  1) The API should respond to a GET request at /api/widgets/
   Message:
     TypeError: Object #<MongoClient> has no method 'collection'
   Stacktrace:
     TypeError: Object #<MongoClient> has no method 'collection'
    at resetDatabase (/home/dev/nimble_node/spec/resetDatabase.js:6:29)
    at /home/dev/nimble_node/spec/e2e/apiSpec.js:23:25
    at /home/dev/nimble_node/node_modules/async/lib/async.js:683:13
    at iterate (/home/dev/nimble_node/node_modules/async/lib/async.js:260:13)
    at async.forEachOfSeries.async.eachOfSeries (/home/dev/nimble_node/node_modules/async/lib/async.js:279:9)
    at _parallel (/home/dev/nimble_node/node_modules/async/lib/async.js:682:9)
    at Object.async.series (/home/dev/nimble_node/node_modules/async/lib/async.js:704:9)
    at null.<anonymous> (/home/dev/nimble_node/spec/e2e/apiSpec.js:19:9)
    at null.<anonymous> (/home/dev/nimble_node/node_modules/jasmine-node/lib/jasmine-node/async-callback.js:45:37)

Finished in 0.01 seconds
1 test, 1 assertion, 1 failure, 0 skipped


Database connection successful

Line 6 of resetDatabase is:

 var collection = dbSession.collection('widgets');

Given that after the error appears, I get the "Database connection successful" message, I think what's happening is that when the tests request the dbSession library, the database hasn't finished running the code to connect. And therefore, I can't get the collection object.

I'm currently reading through the mongodb online manual to see if I can find some hints as to how to do something like this. Any suggestions or pointers would be appreciated.

EDIT 1

To prove that there is a collection method on the MongoClient object, I changed the dbSession.js code to look like this:

'use strict';

var DBWrapper = require('mongodb').MongoClient;
var dbWrapper = new DBWrapper;
dbWrapper.connect("mongodb://localhost:27017/test", function(err, db) {
        if (!err) {
                console.log("Database connection successful");
                dbWrapper = db;
                var collection = dbWrapper.collection('widgets');
                console.log('just created a collection...');
        }
});
module.exports = dbWrapper;

And now, when I start up the http server (index.js), notice the messages:

dev@devbox:~/nimble_node$ sudo nodejs src/backend/index.js 
Server started and listening on port: 8080
Database connection successful
just created a collection...

Answer 1

It could be an async issue.

Your code in dbSessionjs

dbWrapper.connect("mongodb://localhost:27017/test", function(err, db) {
        if (!err) {
                console.log("Database connection successful");
                dbWrapper = db;
        }
});
module.exports = dbWrapper;

Starts the connection at dbWrapper asynchronously , but exports dbWrapper right away, which is then imported in resetDatabase. Thus yes, the connect function may have not yet returned from the async function when you call it in resetDatabase (and is what the log suggests,as the error appears before the success log).

You could add a callback after dbWrapper.connect() returns, in order to actually only be able to use dbWrapper when the connection finished.

(With sqlite, this may not happen as it accesses the DB faster on the commandline).

This may not be your problem but looks like a candidate.

EDIT: Here's a possible example for a callback, but please take note it depends on what you need to do so there are a lot of different solutions. The key is to call a callback function when you are done initializing.

Another solution could be to simply wait, and/or poll (eg chcke a variable 'initialized').

'use strict';

var DBWrapper = require('mongodb').MongoClient;
var dbWrapper = new DBWrapper;

function doConnect(callback) {
  console.log("Initializing DB connection...");
  dbWrapper.connect("mongodb://localhost:27017/test", function(err, db) {
        if (!err) {
                console.log("Database connection successful");
                dbWrapper = db; 
                var collection = dbWrapper.collection('widgets');
                console.log('just created a collection...');
                console.log('calling callback...');
                callback(dbWrapper);
        } else {
          console.log("Error connectingi: " + err);
        }
  }); 
};

doConnect(function(correctDbWrapper) {
    //Now you can use the wrapper
  console.log("Inside callback, now consuming the dbWrapper");
  dbWrapper = correctDbWrapper;
  var collection = dbWrapper.collection('widgets');
});

It's interesting though I never ran into this issue, although I have generally used similar code like yours. I guess because normally I have this DB initialization right at the top, and then have to do lots of initializations on the node app, which gives the app time enough to return from the connect call....