How to raise an ActiveRecord::Rollback exception and return a value together?
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21-08-2019 - |
Question
I have a model that uses a acts_as_nested_set
fork, and I've added a method to the model to save the model and move the node into the set in one transaction. This method calls a validation method to make sure the move is valid, which returns true or false. If the validation fails, I want my save method to raise ActiveRecord::Rollback
to rollback the transaction, but also return false to the caller.
My model looks like this:
class Category < ActiveRecord::Base
acts_as_nested_set :dependent => :destroy, :scope => :journal
def save_with_place_in_set(parent_id)
Category.transaction do
return false if !save_without_place_in_set
if !validate_move parent_id
raise ActiveRecord::Rollback and return false
else
place_in_nested_set parent_id
return true
end
end
end
alias_method_chain :save, :place_in_set
def validate_move(parent_id)
# return true or false if the move is valid
# ...
end
def place_in_nested_set(parent_id)
# place the node in the correct place in the set
# ...
end
end
However, when I call save in a situation that would fail, the transaction is rolled back but the function returns nil
:
>> c = Category.new(:name => "test")
=> #<Category id: nil, name: "test" parent_id: nil, lft: nil, rgt: nil>
>> c.save_with_place_in_set 47
=> nil
>> c.errors.full_messages
=> ["The specified parent is invalid"]
Solution
You could store the value you want returned from the function in a variable and return that outside the transaction block. E.g.
def save_with_place_in_set(parent_id)
return_value = false
Category.transaction do
if !save_without_place_in_set
return_value = false
elsif !validate_move parent_id
return_value = false
raise ActiveRecord::Rollback
else
place_in_nested_set parent_id
return_value = true
end
end
return return_value
end
I've set the return_value to false initially as the only other way you can get out of that transaction block is if one of the other methods raises ActiveRecord::Rollback
I believe.
OTHER TIPS
Because the ActiveRecord::Rollback
exception is handled, but not re-raised by ActiveRecord::Transaction
, I could move my return out of the transaction block, and thus return a value after the transaction is rolled back.
With a little refactoring:
def save_with_place_in_set(parent_id = nil)
Category.transaction do
return false if !save_without_place_in_set
raise ActiveRecord::Rollback if !validate_move parent_id
place_in_nested_set parent_id
return true
end
return false
end
I know it may be a little late, but i ran into the same problem and just found out, that within a transaction block you can simply raise an Exception and rescue that one...Rails implicitly rollbacks the whole transaction. So there is no need for ActiveRecord::Rollback.
For example:
def create
begin
Model.transaction do
# using create! will cause Exception on validation errors
record = Model.create!({name: nil})
check_something_afterwards(record)
return true
end
rescue Exception => e
puts e.message
return false
end
end
def check_something_afterwards(record)
# just for demonstration purpose
raise Exception, "name is missing" if record.name.nil?
end
I'm working with Rails 3.2.15 and Ruby 1.9.3.