[Haskell-cafe] Takusen, postgres and boolean fields

[Christoph Bauer]

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