On Fri, Jul 31, 2009 at 13:39, Murray Steele <murray.ste...@gmail.com>wrote:
> I have to agree with Mislav and Duncan here, if firstname should be unique,
> a finder is not the place to enforce that. Those 2 other "mislav" users
> should not be in the database in the first place! There may be a compelling
> use-case for a find(:only/unique/make_sure_there_is_only_one_result), but
> late detection of invalid data isn't it.
>
To further explain my reasoning:
To me, `first()` is a method I almost exclusively use in the console. I
think of it like "get me the first record that matches some conditions or
scope I specify". If there was a `unique` or `single` method, would the
implementation be much different?
For production code, I use dynamic finders against columns that are
constrained with a unique key—e.g.:
find(1)
find_by_username('mislav')
The implementation for these is (I believe) identical to `first`. I only use
`first` in combination with ordering to say "get me the user with most
comments" or "get me the most recent comment", but this is only for
presentational purposes and you can agree that such a use case doesn't come
often.
But, it's obvious that it's completely wrong to use `first` or `find_by` on
some column(s) that are *not* under a unique constraint. This should always
be used:
find_all_by_username('mislav')
I guess that all I'm trying to say can be summed up as:
1. if the column is unique-constrained, you *should *use find_by_column
(or `first` with conditions or scope);
2. if the column is *not* unique, you *must* use find_all_by_column (or
alternatives);
3. there's no need for an extra method.
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