Add transaction_with for transaction multiple models related

[ryopeko]

This feature supports transaction using multi models.
Using multi models in a transaction...

class Book1 < ActiveRecord::Base
  use_switch_point :db1
end

class Book2 < ActiveRecord::Base
  use_switch_point :db1
end

transaction do
  Book1.with_writable do
    #insert, update, delete, etc...
  end

  Book2.with_writable do
    #insert, update, delete, etc...
  end
end

It is not "DRY".

In this case, Book1 and Book2 has a same db connection.
Therefore, we do not need that write twice a "with_writable".

When we write code like this, we must think that switch "readable, writable".

And, transaction must need a same connection.

Now, using this patch...

Book1.transaction_with(Book2) do
  #insert, update, delete, etc...
end

It is "DRY" and easier to understand the intention.

Also, user does not run of unintended query to DB.
(ex. User did not know Book2 using other DB.)

It will raise a exception in that case.

class Book3 < ActiveRecord::Base
  use_switch_point :db2
end

Book1.transaction_with(Book2, Book3) do
  #insert, update, delete, etc...
end

#=> raise RuntimeError

But, this method is declarative.
You can switch a connection in a block of transaction_with.

[coveralls]

Coverage decreased (-0.12%) when pulling c2283be on ryopeko:feature/transaction_with into 68876d8 on eagletmt:master.

[eagletmt]

Looks good. Thank you 👍

[eagletmt]

Released as v0.4.3 💎
https://rubygems.org/gems/switch_point/versions/0.4.3

[ryopeko]

🎊