Help me the error after replace sqlite3 by using MongoDb and MongoId

I want use MongoDB same as database of Project. I delete gem "sqlite3" and copied 2 gem: gem "mongoid", "~> 3.0.0" gem 'bson_ext' then had error : in `block in replace_gem': Please install the sqlite3 adapter: `gem install activerecord-sqlite3-adapter` (sqlite3 is not part of the bundle. Add it to Gemfile.) (LoadError) and if I copy gem sqlite3 the program ran with MongoDb same as database Plase instruct for me this problem and how to do if I want only MongoDB same as Database. Thanks...

It isn’t enough just to change the gems, you also have to alter the database configuration to be found at config/database.yml. Please check Mongo manual for further details.

Thanks Norbert Melzer I read railscast 238(mongoid) If I use command line:

rails g mongoid:config then in my project have 2 DB :sqlite3+mongoDB And I see data after insert then save in MongoDB If I using both sqlite3+mongoDB above ,please tell me about my program have error with process data after? thanks.