Ruby on Rails

On 28 October 2011 22:46, Christopher J. Bottaro <cjbottaro@gmail.com> wrote:
> Hello,
> What's the best/easiest way to write this delete statement using
> ActiveRecord 3.1?
>
> DELETE e1
>   FROM events e1
>   JOIN events e2
>  WHERE e1.subject_type = e2.subject_type
>    AND e1.subject_id   = e2.subject_id
>    AND e1.origin_type  = e2.origin_type
>    AND e1.origin_id    = e2.origin_id
>    AND e1.id > e2.id

Not answering the question I am afraid, but I think it is unwise to
assume anything about the id sequence. Presumably here you are
assuming that id values are assigned in an increasing sequence, but I
don't think this is necessarily guaranteed in the general case. I
think it might be better to use created_at, if that is what you really
mean. On the other hand if in reality you do not care which one you
delete and have the id test only to make sure that you delete only one
of them then please ignore my comment.

Since you are interested in the best way to code it (rather than just
hacking in the sql) then presumably it is something that happens
routimnely rather than some tidying up operation that you have to do
once. Would it not be possible using validations or similar to ensure
that the duplicate record situation does not happen in the first
place?

Colin

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