[Ur] Exceptions handling

[Gian Perrone]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 8/24/10 5:34 PM, Adam Chlipala wrote:
> Why can't you just check for uniqueness constraint violations in your
> code before inserting into the database?  I can see the case for a
> simple facility for specifying an alternate error-reporting page, but
> more than that doesn't seem worthwhile.  These errors should only come
> up in buggy programs.

Wouldn't checking the uniqueness constraint first require an additional
database query?  My experience is that the web application idiom usually
suggests trying-and-failing in such a case.

Similarly, there does seem to be a case for some kind of exception
handling mechanism for cases where things that aren't obvious bugs cause
queries to fail (e.g. the database server goes away unexpectedly).

My personal preference would just be a simple ML-style "handle"
mechanism, or failing that, the ability to define user-provided callback
functions for the types of exceptions that cannot reasonably be
prevented (e.g. in the simplest case, a global user-defined error
function that takes some error identifier as a parameter and returns a
page), such that one could define error pages within the application
structure.

- --Gian
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.10 (Darwin)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iQEcBAEBAgAGBQJMdBiwAAoJEDd5xfOXfbYMMgsH/RqIYIq5g2DvBzbgc12MyMr8
fx16Sh1HRR1zbyaOUUxX8+4oUMzB6/yZcavPHZHnWDKQ/MrmSbNVCmwb1+Pd2FBg
pMjeOMvLYMkYfdbcQbb4S/YuOkEX/mCcNTfHR/fVNAmKwh/xxl/UegAkS3yyKxtd
k7BzV8+7raPgSNZlZ4XDeNE01yJ5X83anDXukCGhrTzkVK71KGM7/2eS6PnAUO99
tXjhb4r3ia6qtzwXbwFlP/U8EjlZNAB2fKE0RujTr01UXLKmW5YEdKR00g8mDCQ7
YFfSeyccW2qL07mfuIlUz0q+FP3WM/dPertYoj6fu+17fS4ZXWMI8TkQnfIQWLk=
=H3d4
-----END PGP SIGNATURE-----