[Haskell-cafe] Takusen, postgres and boolean fields

[Sasha Shipka]

When I did SELECT statement I handled boolean field as String, and
convert it to Bool.
However when I did update or insert, I must bind those values, then
takusen calls foreign postgres library and function with "?" and
values of proper type. So I cannot use neither Bool neither String in
bindP.

Instead of binding, I've used ugly hack :
"update some_table set some_boolean_field = ? ..." [bindP True, ...]
is replaced with
(printf "update some_table set some_boolean_field = '%s' ... " "t") [...]
I really hate it and I hope there is better way to do it.

On Sat, Apr 25, 2009 at 2:06 PM, Christoph Bauer
<c-bauer-olsbruecken at t-online.de> wrote:
> Sasha Shipka <xaotuk at gmail.com> writes:
>
>> Let say one has to do something similar to this:
>>
>> execDML $ cmdbind (sql "update some_table set some_boolean_field = ?
>> where ...") [bindP True, ...]
>>
>> When I do it, I have an error:
>>
>> DBError ("42","804") 7 "ERROR:  42804: column \"some_boolean_field\"
>> is of type boolean but expression is of type text ..."
>>
>> I've noticed that when I read boolean fields from postgres it reads
>> them as string "t" or "f". So I also tried bindP "t" and had same
>> error.
>
> Indeed, I also have such problems in my application [1] in
>   SELECT boolean_field from TABLE.
>
> My workaround is: I defined a plpgsql function
>
> CREATE OR REPLACE FUNCTION HBoolean(v IN BOOLEAN)
> RETURNS TEXT AS $$
> BEGIN
>   IF v THEN RETURN 'True';
>   ELSE RETURN 'False';
>   END IF;
> END;
> $$ LANGUAGE plpgsql;
>
>
> and rewrite my query as
>
>   SELECT HBoolean(boolean_field) from TABLE
>
> and  takusen converts it to Bool.
>
>
> For performance reason you may convert from text to boolean (but keep
> bindP True). If there is a better solution, I'm also glad to know it.
>
> Christoph Bauer
>
>
> [1] http://www.communitystory.de
>