Rollback transactions without exceptions

rubyonrails-core
1

There is only one way to rollback a transaction in Rails: using an exception.

Although an exception may be used to rollback a transaction is OK in certain scenarios, i think it should not be used to rollback all of them. Making a nice differentiation between errors and exceptions makes the code more readable and easy to maintain (it looks awkward to write an exception to handle a name length validation that is not honored in order to rollback a transaction, when ther is already a .valid? method related to the model that handle that)

Basically i think it would be nice to honor the next two rules:

  1. “Exceptions are not meant to be expected, that is why they are called exceptions”

  2. “Don’t use exceptions for control flow”

Some benefits:

  1. We will not have two different ways to handle the same model-validation: so we can use .valid? and model’s errors array to handle model validations within (or not) a transaction

  2. Good differentiation of what an error is (something that we expect to happen) and an exception (something that is not expected to happen) which is a perfect match for this proposed idea of having a proper ActiveModel::Error object which can be used within a transaction too, instead a Exception

  3. Error handling within a Transaction will easier to write and read, for example, something around this:

In the model…

class Model < ApplicationRecord

def some_method(…)

…

Transaction do

rollback unless user.save && invite.save

end

Althoug we roolbacked the transaction this gets executed because we

did not use an Exception, just regular model valiation

user, invite

…

end

end

In the controller

class SomeController < ApplicationController

def some_action

user, invite = Model.some_method(…)

If user && invite

All OK, render json etc

else

Something went wrong… render errors using ActiveRecord::Error related to user and/or invite models

end

…

end

end