database.md

Database

The first thing to do in order to make queries to the database is to open one. This can be done with the Db constructor.

var mongodb = require("mongodb"),
    mongoserver = new mongodb.Server(host, port, server_options),
    db_connector = new mongodb.Db(name, mongoserver, db_options);
    
db_connector.open(callback);

• host is a server hostname or IP
• port is a MongoDB port, use mongodb.Connection.DEFAULT_PORT for default (27017)
• server_options see Server options
• name is the databse name that needs to be opened, database will be created automatically if it doesn't yet exist
• db_options see DB options

Server options

Several options can be passed to the Server constructor with options parameter.

• auto_reconnect - to reconnect automatically, default:false
• poolSize - specify the number of connections in the pool default:1
• socketOptions - a collection of pr socket settings

Socket options

Several options can be set for the socketOptions.

• timeout = set seconds before connection times out default:0
• noDelay = Disables the Nagle algorithm default:true
• keepAlive = Set if keepAlive is used default:0, which means no keepAlive, set higher than 0 for keepAlive
• encoding = 'ascii'|'utf8'|'base64' default:null

DB options

Several options can be passed to the Db constructor with options parameter.

• native_parser - if true, use native BSON parser
• strict - sets strict mode, if true then existing collections can't be "recreated" etc.
• pk - custom primary key factory to generate _id values (see Custom primary keys).
• forceServerObjectId - generation of objectid is delegated to the mongodb server instead of the driver. default is false
• retryMiliSeconds - specify the number of milliseconds between connection attempts default:5000
• numberOfRetries - specify the number of retries for connection attempts default:3
• reaper - enable/disable reaper (true/false) default:false
• reaperInterval - specify the number of milliseconds between each reaper attempt default:10000
• reaperTimeout - specify the number of milliseconds for timing out callbacks that don't return default:30000
• raw - driver expects Buffer raw bson document, default:false

Opening a database

Database can be opened with Db method open.

db_connector.open(callback);

callback is a callback function which gets 2 parameters - an error object (or null, if no errors occured) and a database object.

Resulting database object can be used for creating and selecting collections.

db_connector.open(function(err, db){
    db.collection(...);
});

Database properties

• databaseName is the name of the database
• serverConfig includes information about the server (serverConfig.host, serverConfig.port etc.)
• state indicates if the database is connected or not
• strict indicates if strict mode is on (true) or off (false, default)
• version indicates the version of the MongoDB database

Database events

• close to indicate that the connection to the database was closed

For example

db.on("close", function(error){
    console.log("Connection to the database was closed!");
});

NB! If auto_reconnect was set to true when creating the server, then the connection will be automatically reopened on next database operation. Nevertheless the close event will be fired.

Sharing the connections over multiple dbs

To share the connection pool across multiple databases you database instance has method db

db_connector.db(name)

this returns a new db instance that shares the connections off the previous instance but will send all commands to the database name. This allows for better control of resource usage in a multiple database scenario.

Deleting a database

To delete a database you need a pointer to it first. Deletion can be done with method dropDatabase.

db_connector.open(function(err, db){
    db.dropDatabase()
});

Custom primary keys

Every record in the database has an unique primary key called _id. Default primary keys are 12 byte hashes but a custom key generator can be used for something else. If you set _id "by hand" when inserting records then you can use whatever you want, primary key factory generates _id values only for records without ones.

Example 1: No need to generate primary key, as its already defined:

collection.insert({name:"Daniel", _id:"12345"});

Example 2: No primary key, so it needs to be generated before save:

collectionn.insert({name:"Daniel"});

Custom primary key factory is actually an object with method createPK which returns a primary key. The context (value for this) for createPK is left untouched.

var CustomPKFactory = {
    counter:0,
    createPk: function() {
        return ++this.counter;
    }
} 

db_connector = new mongodb.Db(name, mongoserver, {pk: CustomPKFactory});