[Ur] Constructing SQL WHERE clause at runtime

[Sergey Mironov]

Thanks, Adam. Looks like it is what I need. I'll try the code soon.

Regards,
Sergey

2015-06-03 0:54 GMT+03:00 Adam Chlipala <adamc at csail.mit.edu>:
> I could swear I sent an example of this kind to the list years ago, but I
> couldn't find it quickly, so here's a new one!  The function [matching] is
> fine to call with expressions that are only determined at runtime.
>
> I do believe all of the ingredients (e.g. parser extensions) here are
> documented in the manual, but admittedly it's not trivial to piece them all
> together into a sufficient intuitive understanding.
>
> table t : { A : int, B : int }
>
> datatype int_exp =
>          A
>        | B
>        | Plus of int_exp * int_exp
>
> datatype bool_exp =
>          Eq of int_exp * int_exp
>        | And of bool_exp * bool_exp
>
> fun int_exp (e : int_exp) : sql_exp [T = [A = int, B = int]] [] [] int =
>     case e of
>         A => (SQL t.A)
>       | B => (SQL t.B)
>       | Plus (e1, e2) => (SQL {int_exp e1} + {int_exp e2})
>
> fun bool_exp (e : bool_exp) : sql_exp [T = [A = int, B = int]] [] [] bool =
>     case e of
>         Eq (e1, e2) => (SQL {int_exp e1} = {int_exp e2})
>       | And (e1, e2) => (SQL {bool_exp e1} AND {bool_exp e2})
>
> fun matching (e : bool_exp) : transaction (list {A : int, B : int}) =
>     queryL1 (SELECT * FROM t WHERE {bool_exp e})
>
>
>
> On 06/02/2015 03:43 PM, Sergey Mironov wrote:
>>
>> Hi! I am trying to implement a post-query filter. Of cause it is
>> possible to use [queryL] followed by server-side filtering code, but
>> using the DB engine is a better solution in my case.
>>
>> Typically, I'd like to convert a list of string patterns to a WHERE
>> clause of the form  (OR Field LIKE {[patter1]} OR Filed LIKE
>> {[pattern2]} OR ... pattern x ...  OR FALSE)
>>
>> I think it should be possible to write it in Ur/Web, but I can't
>> remember any examples demonstrating this. Is it really possible?
>
>
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