On Sun, Feb 15, 2015 at 08:53:28AM -0800, Jeremy Evans wrote:
> On Sunday, February 15, 2015 at 12:52:27 AM UTC-8, Matt Palmer wrote:
> > Long version:
> >
> > I tried to define a where clause which contained a modulus calculation,
> > like
> > so:
> >
> > db[:ex].where { col % 3 == 0 }
> >
> > Much to my surprise, this bombed, telling me
> >
> > NoMethodError: undefined method `%' for #<Sequel::SQL::Identifier
> > @value=>:col>
> >
>
> This is wrong in two places. First, equality is done via hashes, second,
> the modulus operator is only defined for columns known to be numeric.
>
> db[:ex].where{{col.sql_number % 3 => 0}}
Fair enough. Why does modulo need to be called against a numeric column,
while the other arithmetic-only operators can be applied to anything? I get
why '+' is valid for strings (nice one, by the way), but the others aren't
valid Ruby for Strings.
> > "Hmm, OK", says I, "I'll see if I'm doing this totally wrong, by trying
> > division":
> >
> > db[:ex].where { col / 3 == 0 }
> >
> > This doesn't exception out, but instead produces the SQL
> >
> > SELECT * FROM "ex" WHERE false
> >
> > That's... not right.
>
> Sequel doesn't override the equality operator (#==), as that would make it
> very difficult to determine equality at the ruby level.
With the example you provide, I now understand why #== can't be overridden.
> I'd definitely welcome documentation updates that better explain things,
> though.
Then that is the patch I shall endeavour to produce.
Thanks,
- Matt
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