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Expresser Database

The Database module is a MongoDB wrapper and has 3 main methods: get , set and del . There's also a count helper that works with newer versions of MongoDB.

It also provides a super simple failover mechanism to switch to a backup database in case the main
database fails repeatedly. This will be activated only if you set the settings.database.connString2 value. Please note that Expresser won't keep the main and backup database in sync! If you wish to keep them in sync you'll have to implement this feature yourself - we suggest using background workers with IronWorker (

If the setting is enabled, the Database module will automatically figure out the connection details for the following MongoDB services: AppFog, MongoLab, MongoHQ.

If you're using Backbone.js or any other framework which uses "id" as the document identifier, you might want to leave the settings.database.normalizeId true, so the Database module will parse results and convert "_id" to "id" on output documents and from "id" to "_id" when saving documents to the db.

Sample code

The following example illustrates how to get a document having "username = igor" from collection "users" and duplicate it to a document having "username = igor2". Errors will be logged using the Logger module.

    var expresser = require("expresser");

    var setCallback = function(err, result) {
        if (err) {
            expresser.logger.error("Can't save document with username igor2.", err);
        } else {
  "Document duplicated!", result);

    var getCallback = function(err, result) {
        if (err) {
            expresser.logger.error("Can't get document with username igor.", err);
        } else {
            var user = result[0];
            user.username = "igor2";
            delete user["id"];
            expresser.database.set("users", user, setCallback);

    expresser.database.get("users", {username: "igor"}, getCallback);

For detailed info on specific features, check the annotated source on /docs folder.

Last edited Feb 12, 2014 at 11:51 PM by igoramadas, version 5


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