Rails - Apr 2005 - Feedback/help on possible ActiveRecord patch/research?

I needed a way to add automatic saving of previous versions of 
arbitrary tables in my web app''s database, because I wasn''t
sure what
tables I''d want to do this with and with what fields in them, and I 
came up with this rough and sort-of tested solution:

1. For the table I want to save previous versions of, I create a table 
with its singular name, plus "_versions", so that my
"articles" table
has an "article_versions" counterpart.

2. My "articles" table has a field called "body", and some
other fields
for its title, what newsletter it belongs to, etc. I want to keep 
versions of the "body" field only. So, in the
"article_versions" table,
I create a field called "body", and I also create a field called 
"article_id", and a field called "created_at".

3. This point is the point at which I need help! What I do here is 
include a module that has a modified "save" method and methods for 
getting previous versions of the given article, and create a method in 
my Article class called "attributes_to_save_in_versions", which
returns
an array of the fields I want to save in previous versions. Right now, 
the module is called "KeepsVersionsOf", but I''d like to do
something
like in ActiveRecord Associations, where I just type "keeps_versions_of 
:body" or something.

The module is here: http://mdaines.com/code/keeps_versions_of.rb (It''s 
not all that long, but I don''t know the protocol for posting code here,
so I thought I better just include a link.)

One thing that needs to be done -- if a record is destroyed, the 
previous versions aren''t. I suppose this would involve doing something 
to the "destroy" method, but I can''t quite figure out how to
use, say,
method aliasing to put my destroy code after the existing code without 
touching it. (Same with the "save" method.)

If possible, I would like feedback on this. Also, if possible, advice 
on how to prepare a patch of it.


- Michael Daines

On 21/04/2005, at 11:42 AM, Michael Daines wrote:
> I needed a way to add automatic saving of previous versions of 
> arbitrary tables in my web app''s database, because I
wasn''t sure what
> tables I''d want to do this with and with what fields in them, and
I
> came up with this rough and sort-of tested solution:
Why not use ActiveRecord::Observer to observe the articles on 
before_update and before_destroy? Combine these with a table view 
giving you only the articles that have ''DELETED_FLAG = 1'' and
vice
versa and you''ll be laughing -- unless of course your dbms
doesn''t have
table views... then life isn''t quite so sweet =)

- tim lucas