Rails 3：将 model 迁移到 MongoDB

Question

I have a few models in my existing Rails 3 app that are completely non-relational to the other models in the application's ecosystem. The underlying data is incredibly large and it would benefit in being moved from my relational db (MySQL) to a non-relational document data store, such as MongoDB. The problem I currently have is that the model is instantiated in several places in my code base using Foo.create, Foo.new etc. My question(s) are the following:

• What is the ideal way for me to use MongoDB and MySQL side by side in a Rails 3 app?

• Should I use a 'ghost' method on ActiveRecord.create for the model I want to migrate to MongoDB and write the logic there that persists it to a different data store? This sounds very brittle, but it's just a thought.

Answer 1

1) Just do it, using mongoid or mongo_mapper. Both are great!

2 ) NO! Replace ActiveRecord superclass with that of mongoid or mongo_mapper.

The only difficult thing about polyglot persistence is to remember the word, polyglot. Don't over-complicate. The models that inherit ActiveRecord are mapped to the SQL-db, the models that don't inherit it, are not. Simple as that. Same with the models that inherit the Mongo-ORM-class, only they are mapped to MongoDB.

I use postgreSQL alongside MongoDB (mongo_mapper). One awesome thing for everybody to try out, is storing errors in Mongo docs. Beats *.log files.

Final note: Having Foo.create and Foo.new at multiple places is a code smell and you should probably refactor according to DRY and SRL. Just a friendly note:)

Answer 2

There's no inherent problem in having some classes in ActiveRecord and some in Mongoid, just transfer the data over.

This is a rather simplistic example, but below you would still be able to say @account.transactions

class Account < ActiveRecord::Base

  def transactions
    Transaction.where(:account_id=>self.id).all
  end

end

class Transaction
  include Mongoid::Document
  field :account_id, :type=>Integer

  def account
    Account.find(account_id)
  end
end

Answer 3

Look at mongoid , an orm for mongodb. It uses ActiveModel and can essential behave just like your ActiveRecord based models. Once you include the mongoid document class in your model, add the fields and config the connection it should be fairly transparent.