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database.rb

Multiple Collections and Databases in Mongo Model.

By default models use default database, but You can use multiple databases and save model to any collection. create This is advanced topic, usually You don’t need these features, You can safely ignore this sample if You don’t need such features.

In this example we’ll create Post model and save it to different databasescreate and collections.

 
require 'mongo/model'

Connecting to test database and cleaning it before starting.

 
Mongo::Model.default_database_name = :default_test
Mongo::Model.default_database.clear
db = Mongo::Model.default_database

Collections

 

      		
    

    

      
        

          
        

        
Defining Post.

      		
      
        
class Post
  inherit Mongo::Model
  collection :posts

  attr_accessor :text
end

      		
    

    

      
        

          
        

        
Creating post in default :posts collection.

      		
      
        
post = Post.new text: 'Zerg infestation found on Tarsonis!'
post.save
p db.posts.count                                 # => 1

      		
    

    

      
        

          
        

        
Creating post in custom collection

      		
      
        
post = Post.new text: 'Norad II crashed!'
post.save collection: db.drafts
p db.drafts.count                                # => 1

      		
    

    

      
        

          
        

        
Databases

      		
      
        

      		
    

    

      
        

          
        

        
Let’s create model for Article and save it in another database.
By default model use Mongo::Model.default_database, but we can use customcreate
database and collection.

      		
      
        
class Article < Post
  db :default_test2
  collection :articles
end

      		
    

    

      
        

          
        

        
Now our Article uses :default_test2 database.

      		
      
        
p Article.db.name                                # => "default_test2"

      		
    

    

      
        

          
        

        
But in real life scenario it’s not very convinient to use real database name
in models, usually it’s more convinient to use aliases and specify realcreate
names in config.
create
We can do this by owerriding Mongo.db method.

      		
      
        

      		
    

    

      
        

          
        

        
Here’s our config, it map :db2 alias to the :default_test2 real name.

      		
      
        
DB_CONFIG = {db2: :default_test2}

      		
    

    

      
        

          
        

        
Overriding Mongo.db method and making it use our DB_CONFIG.

      		
      
        
module Mongo
  class << self
    alias_method :db_without_config, :db
    def db name
      name = DB_CONFIG[name] || name
      db_without_config name
    end
  end
end

      		
    

    

      
        

          
        

        
Now we can use database alias in our models.

      		
      
        
class Article
  db :db2
end

      		
    

    

      
        

          
        

        
The :db2 alias mapped to the :default_test2 name.

      		
      
        
p Article.db.name                                # => "default_test2"

      		
    

    

      
        

          
        

        
In this example we covered how to use multiple collections
and databases.