# Multidatabase transactions

**URL:** <https://www.ruby-forum.com/t/multidatabase-transactions/182224>\
**Category:** Rails\
**Created:** [January 25, 2010, 12:46pm UTC](https://www.ruby-forum.com/t/multidatabase-transactions/182224 "2010-01-25T12:46:10Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![deepak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7bcc69/32.png) [@deepak](https://www.ruby-forum.com/u/deepak)\
**Post date:** [January 25, 2010, 12:46pm UTC](https://www.ruby-forum.com/t/multidatabase-transactions/182224/1 "2010-01-25T12:46:10Z")

</div>

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.