In normal rails application contain one database,but if we want rails application having more than one database that is multiple data base. we can achieve this using multiple way.one of the way is i am showing here.it’s just 3 steps.
Lets take an e.g Project has many milestone and milestone has many task
In normal scenario model looks like following way
class Project < ActiveRecord::Base has_many :milestones end class Milestone < ActiveRecord::Base has_many :tasks belongs_to :project end class Task < ActiveRecord::Base belongs_to :milestone end
Now we want that milestone is stored on milestone_db database and task on task_db database
Now to achieve this we have to do the following steps
1) Edit Database.yml
milestone_dev: reconnect: false encoding: utf8 username: <user_name> adapter: mysql database: milestone_db pool: 5 password: <password> task_dev: reconnect: false encoding: utf8 username: <user_name> adapter: mysql database: task_db pool: 5 password: <password>
Now create milestone_db and task_db database.
2) Edit milestone.rb and task.rb
class Milestone < ActiveRecord::Base #add this line to use milestone_db self.establish_connection :milestone_dev has_many :tasks belongs_to :project end class Task < ActiveRecord::Base #add this line to use task_db set_table_name "tasks" belongs_to :milestone end
3) After editing model edit migration file
class CreateMilestones < ActiveRecord::Migration def self.connection Milestone.connection end ..... end
Now rails application is ready with multiple database.
12 comments On Multiple database in rails
Good write up.
I was wondering though, how would you handle migrations in this situation?
Yes fine. This is saved my time. But schema.rb contains the tables structures of only the database under the default ‘development’ environment. Table structures of other databases was not found. How to generate those too.
Thanks and Regards
Great guide.
But i’m facing troubles after I did this and I tried to use rake db:migrate.
All the tables gets created in one database instead of creating one of the models in another specied (like in your example) database.
Do you have any tips/tricks up your sleeves?
Best regards
Hi,
sorry for late reply,i have gone through rake task of db migrate it invoke db:schema:dump task.
It will do
File.open(ENV['SCHEMA'] || "#{RAILS_ROOT}/db/schema.rb", "w") do |file|ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
end
so when we are migrating if we want to specify following self.connection
add this line to migration and it will create another schema file(in this case schma_mile_dev.rb)
File.open("#{RAILS_ROOT}/db/schema_milestone_dev.rb", "w") do |file|ActiveRecord::SchemaDumper.dump(self.connection, file)
end
And in schema_milestone_dev.rb
ActiveRecord::Schema.define(:version => 0) do
ActiveRecord::Base.establish_connection :milestone_dev
end
and run
rake db:schema:load SCHEMA="#{RAILS_ROOT}/db/schema_milestone_dev.rb"it will load schema to database but in respective database.
You can further customize rake task to simplify this process
Have you edit migration file? Please if not update it.If it is still issue please ping me again i will surely look into it.
Hi i have a problem
I am running 2 rails apps.
App1 can access App2’s database.
Now in App1 i have course.rb and in App2 also i have course.rb
How can i say “self.establish_connection :App2’s database” in App1 course.rb”
How can i come out of this problem ??
Hi,
Add another configuration in database.yml(APP2 setting) and try it out.
I don’t know weather it is useful for you or not might be active resource is useful for you.
Thanks a lot for sharing the stuff, it was very helpful 🙂
hi
i have develop the train_develop database and also train_pro, train_test,train_test1,train_test2…totally 8 database under a application.all database has same structure(tables everything).would i connect each database as properly?if possible means send a coding hints as soon as possible.thanks
Hi,
Why you need different database for for same structures.If there are multiple environment like staging,development etc
you can set environment and for respective environment you can add to database.yml file.
Start server with respective environment.It will pick database as you mention in database.yml
If this is not a case let me know i will guide you.
Thank you very much, I’ve found much more complicated solutions, and this is pretty simple, no monkey patches
I could make db:schema:dump work… I did monkey patch with:
2 namespace :db do
3 namespace :schema do
4 task :dump do
5 File.open(ENV[‘SCHEMA’] || “#{RAILS_ROOT}/db/schema.rb”, “w”) do |file|
6 next unless (self.connection.is_a? ActiveRecord::ConnectionAdapters::AbstractAdapter rescue nil)
7 ActiveRecord::SchemaDumper.dump self.connection, file
8 end
9 end
10 end
11 end