Ruby-on-rails 如何引发 ActiveRecord::Rollback 异常并一起返回值？

How to raise an ActiveRecord::Rollback exception and return a value together?

提问by Daniel Vandersluis

I have a model that uses a acts_as_nested_setfork, 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::Rollbackto rollback the transaction, but also return false to the caller.

我有一个使用acts_as_nested_setfork的模型，我在模型中添加了一个方法来保存模型并将节点移动到一个事务中的集合中。此方法调用验证方法以确保移动有效，该方法返回 true 或 false。如果验证失败，我希望我的 save 方法提升ActiveRecord::Rollback以回滚事务，但也向调用者返回 false。

My model looks like this:

我的模型看起来像这样：

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:

但是，当我在失败的情况下调用 save 时，事务会回滚但函数返回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"]

回答by Shadwell

You could store the value you want returned from the function in a variable and return that outside the transaction block. E.g.

您可以将要从函数返回的值存储在变量中，然后在事务块之外返回该值。例如

  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::RollbackI believe.

我最初将 return_value 设置为 false 作为摆脱该事务块的唯一其他方法是ActiveRecord::Rollback我相信其他方法之一是否引发。

回答by Daniel Vandersluis

Because the ActiveRecord::Rollbackexception 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.

因为ActiveRecord::Rollback异常被处理，但不是由 重新引发ActiveRecord::Transaction，我可以将我的返回移出事务块，从而在事务回滚后返回一个值。

With a little refactoring:

稍微重构一下：

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

回答by Matteo

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.

我知道现在可能有点晚了，但我遇到了同样的问题，并且刚刚发现，在事务块中，您可以简单地引发一个异常并挽救那个异常……Rails 隐式地回滚整个事务。所以不需要 ActiveRecord::Rollback。

For example:

例如：

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.

我正在使用 Rails 3.2.15 和 Ruby 1.9.3。