Rails - Dec 2006 - Creating/updating multiple associated objects at the same time

The problem: For me it''s a common case that I want to create or update 
multiple associated objects at the same time from a single params hash.

The restrictions: This is clearly functionality that belongs in the 
model. The operation obviously has to be transactional, either all 
objects are created/updated or none.

A solution. Well, it works for me.

  def initialize(attributes = nil)
    # initialize already executes inside a transaction
    # there''s no point in adding a further transaction block
    base_attributes, child_attributes       split_attributes(attributes)
    super(base_attributes)
    attach_children(child_attributes)
  end

  # Use this instead of update_attributes in controller.
  def update_properties!(attributes)
    base_attributes, child_attributes       split_attributes(attributes)
    self.class.transaction do
      attach_children(child_attributes)
      update_attributes(base_attributes) ||
        raise(ActiveRecord::RecordInvalid, self)
    end
  end

  def split_attributes(attributes)
    ...
  end
  
  def attach_children(attributes)
    # find, create, or update the children based on given attributes
    # raises an exception if anything goes wrong
  end

As I said, this works for me, but it doesn''t feel nice and clean. I
have
to override initialize, which I''d rather not do and leave this method 
entirely to ActiveRecord. Similar for updating. Overriding 
update_attributes suitably doesn''t seem feasible[*], and I
wouldn''t
want to anyway.

[*] If anything goes wrong, the surrounding transaction has to be 
aborted to cause a rollback. This can only be done *reliably* by 
raising an exception from update_properties! as the method might be 
executing in an outer transaction block in which case an exception has 
to be raised out of that transaction block to actually abort the 
transaction.

As I''m pretty sure that I''m not the only one whose trying to
tackle this
problem, I''m really interested in other approaches.

Michael

-- 
Michael Schuerig
mailto:michael-q5aiKMLteq4b1SvskN2V4Q@public.gmane.org
http://www.schuerig.de/michael/

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