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LABS
Mongoid Migrations using the Mongo Driver

In my last post, I modified a Mongoid::Document during a migration in order to access fields that where no longer defined in the class. This time I am using the mongo ruby driver directly to migrate data.

Since I am using Mongoid in this project, I will be using it to access the dependent mongo driver. This will prevent me from having to provide mongo with a connection string in my migration. I am also using mongoid_rails_migrations to roll out the change.

Initial Design

class User
  include Mongoid::Document
  field :first_name
  field :last_name
end

New Design

class User
  include Mongoid::Document
  field :name
end

Migration

class MergeUsersFirstAndLastName < Mongoid::Migration
  def self.up
    #get the mongo database instance from the Mongoid::Document
    mongo_db = User.db

    #query the collection for the fields needed for the migration
    user_hashes = mongo_db.collection("users").find({}, :fields => ["first_name", "last_name"])

    user_hashes.each do |user_hash|
      new_name = "#{user_hash['first_name']} #{user_hash['last_name']}"

      #update the new field
      mongo_db.collection("users").update({"_id" => user_hash["_id"]}, {"$set" => {"name" => new_name}})

      #remove old fields from collection
      mongo_db.collection("users").update({"_id" => user_hash["_id"]}, {"$unset" => { "last_name" => 1, "first_name" => 1}})
    end
  end
end

Resources

MongoDB Ruby Driver Tutorial

Querying with MongoDB Ruby Driver

Updating with MongoDB Ruby Driver

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