Re: [Haskelldb-users] 'IN' operator

[Bjorn B. <bri...@cs...>]

On Jul 5, 2006, at 3:20 PM, Matthias Radestock wrote:

> I want to be able to select records from a table based on a list of =20=

> ids
> I have been given. In SQL I would write
>
>   SELECT ... FROM ... WHERE id IN (10,2,13,4,...)
>
> How do I do this in haskelldb?
>
> Looking at the haskelldb code and docs, it appears that the 'IN'
> operator isn't implemented - it's present in PrimQuery but nothing at
> the higher-levels produces it.
>
> Have I missed something? Is there perhaps a different way to construct
> these kinds of queries?

That would be a nice feature to have, but it isn't implemented at the =20=

moment. You are very welcome to have a go at it and send me a patch.

One workaround that I have used (I don't know why I didn't just =20
implement IN instead) is to use something like:

t <- ...
restrict (foldr (\x y -> t!field .=3D=3D. x .||. y) (const True) values)

(not actual tested code, I just made it up since I couldn't find =20
where I had done it). That is, just use a disjunction of a bunch of =20
equalities.

/Bj=F6rn