Multidatabase transactions

Rails
1

hi,
i wanted to implement multidatabase transactions, in a project of
mine.

The AWDR book by DHH and Sam Ruby, says that rails does not support
easily the usecase where we are updating multiple databases
concurrently.

eg:
==== CODE START ====
the Account and User models have different connections.

acc1 = Account.find(10)
acc1 = Account.find(20)

begin
Account.transaction do
acc1.withdraw(100)
acc2.deposit(100)

User.transaction do
   acc1.user.balance = acc1.balance
   acc1.user.save!
   acc2.user.balance = acc2.balance
   acc2.user.save!
end
raise "the Account model will be rolledback not not the User model

as both the classes have diff. connections"
end
rescue Exception => err
puts “Error | #{err.class} #{err.to_s} #{err.backtrace}”
#to get the current values in the db
[acc1.acc2].each {|x| x.reload }
end

what will happen is that the changes for:
acc1.withdraw(100)
acc2.deposit(100)

will be rolled-back

but the changes for:
acc1.user.balance = acc1.balance
acc2.user.balance = acc2.balance

will not be rolledback, as they are on different database connections.

==== CODE END ====

How to solve this, how to keep the transaction across db
connections.
any ideas?

questions?

  1. can i manually maintain the transaction, rather than a DSL. the DSL
    enforces a nesting relationship but i want a grouping
    relationship.
  2. This same problem does not occur if the db connection is the same,
    how?
  3. how do we check that two db connections are different,
    is .connection == .connection sufficient?
  4. what does the option key :joinable do in active_record/
    connection_adapters/abstract/database_statements.rb. it is not
    mentioned in the docs.

i wanted to implement multidatabase transactions. How do we do this?
Has anyone faced this problem?

thanks for the help,
deepak.