firebird-devel

[Firebird-devel] Exceptions with custom message text

[Marco M. <mm...@ly...>]

Hi, as far as I remember, exception with a message that can build "on 
the fly" in a trigger or a SP is available for FB 1.5 or planned.
Thinking about what I actually need in my database, I think that a 
"customisable" message would be better, I mean, something like:
EXP_WRONG_CODE = 'THE CODE %s IS WRONG, TRY AGAIN';
And in the SP
EXCEPTION EXP_WRONG_CODE(CAST(NEW.ITEMCODE AS VARCHAR(10)));
This is much better than having to assign all the message only to change 
a little but fundamental information.
What do you think about it?
Regards
Marco Menardi

Re: [Firebird-devel] Exceptions with custom message text

[Mike N. <ta...@al...>]

I can't really comment on the utility of the proposal. I did however
start to think about some technical aspects of it.

Marco Menardi wrote:

> EXP_WRONG_CODE = 'THE CODE %s IS WRONG, TRY AGAIN';

I'm not so sure about the syntax of parameter substitution here. There
are (at least) two issues:
1. The user have to learn/use different specifiers depending on data
type.
2. It makes localisation awkward, since the position would be fixed
relative any other substitution needed in the same exception.

What about "{1}", "{2}" ... "{n}"? That would handle the seond problem
outlined above, allowing something like FOO='Hey {3}, you can't {1}
record #{2}!', and at use
EXCEPTION FOO('delete', old.rec_id, 'Mike')

It would be only one type used for these substitution, string. Any type
used in the substitution would have to have to be convertible to string.
If someone really had the urge or need to cast data types back and forth
(maybe to truncate incoming strings) I see no reason to disallow it, but
for the general case such casts wouldn't have to be performed - it would
know how to turn e.g. an integer into a string.

Just some technical ideas on a subject I otherwise haven't even
considered.

/Mike

Re: [Firebird-devel] Exceptions with custom message text

[Alex P. <pe...@in...>]

> 
> What about "{1}", "{2}" ... "{n}"? That would handle the seond problem
> outlined above, allowing something like FOO='Hey {3}, you can't {1}
> record #{2}!', and at use
> EXCEPTION FOO('delete', old.rec_id, 'Mike')
> 

This syntax with string-only substitution sounds good for me. 
Must we enable exceptions like:
FOO='Hey {3}, you can't {1} record #{3}!'
Should we treat this as a bug or:
'Hey Mike, you can't delete record #Mike!'
Should we require precise match for number of exception params
and {n} in exception or may replace missing one with empty strings
and ignore unneeded?

Alex.

Re: [Firebird-devel] Exceptions with custom message text

[Mike N. <ta...@al...>]

Alex Peshkov wrote:

> This syntax with string-only substitution sounds good for me.
> Must we enable exceptions like:
> FOO='Hey {3}, you can't {1} record #{3}!'
> Should we treat this as a bug or:
> 'Hey Mike, you can't delete record #Mike!'

The latter. Even if perhaps a bit odd to not use parameter 2 in this
example, I don't see why reusing parameters like this would be a
problem.

> Should we require precise match for number of exception params
> and {n} in exception or may replace missing one with empty strings
> and ignore unneeded?

I think parameters that are requested in format string but not present
at the point of use (i.e. the exception clause) should be allowed, at
least we shouldn't SEGV. :-)

What such missing parameter should be replaced with, I do not know. An
empty string is one possibility, but perhaps the string "{missing
exception parameter n}", where 'n' would be the parameter number
expected, such as "{3}". I'd also expect that string to be hard-coded
and not subject to localisation.

What could pose another problem, maybe even more interesting, would be
to give too many parameters. What should the outcome of that be? I
believe it should do substitution as requested, but maybe display even
the error? Something like:

Hey nn, ... (the real message)
Too many parameters to exception FOO from SP BARF. Expected 3 but got 6
parameters.
param4: "Symphony of destruction"
param5: "3.1415926535897932384626433832795"
param6: "80:4711"

The "from SP BARF" might or might not be a good thing to have, to help
in tracking down such offenders.


But this is still all an academic discussion, right? :-)

/Mike

Re: [Firebird-devel] Exceptions with custom message text

[Alex P. <pe...@in...>]

> 
> But this is still all an academic discussion, right? :-)
> 
> /Mike
> 

I think that this is discussion concerning 2.0 :)
Alex.

Re[2]: [Firebird-devel] Exceptions with custom message text

[Nickolay S. <sk...@bs...>]

>>
>> But this is still all an academic discussion, right? :-)
>> 
>> /Mike
>> 

> I think that this is discussion concerning 2.0 :)

I think it is still possible to bribe Dmitry to implement this
feature in 1.5. ;))
Mike, if you really need this feature - it is small and is really easy
to implement. It can sneak to FB1.5 during beta stage I think...

> Alex.

Nickolay Samofatov

RE: Re[2]: [Firebird-devel] Exceptions with custom message text

[Dmitry Y. <di...@us...>]

Nickolay,

> > I think that this is discussion concerning 2.0 :)
>
> I think it is still possible to bribe Dmitry to implement this
> feature in 1.5. ;))

Sorry, but it's not problem for Dmitry to just write small SP in his
databases to handle parameters in exception messages ;-)


Dmitry

Re: [Firebird-devel] Exceptions with custom message text

[Marco M. <mm...@ly...>]

What kind of 'magic' are you telling about?
I know how to raise an exception, but not how change the message in a SP...
I think that ofter a more precise (informative) exception message is 
welcome, but we must take care to avoid:
a) exception definition proliferation, i.e. you end up with 1,000 
different exception just to be more informative
b) "build on the fly" exception, where you end up with only one 
exception, and build it's message "as needed".
My suggestion is to create something like "exception families", or 
"cutomizable exception", so for invalid date you can have
EXP_INVALID_QUANTITY = 'THE QUANTITY {1} IN {2} IS TOO SMALL, MINIMUM {3}';

and in some trigger, have:
IF (NEW.BEER_QT < 100) THEN
   EXCEPTION EXP_INVALID_QUANTITY(NEW.BEER_QT, 'beer', '100');
IF (NEW.FIREBIRD_ORDERS_QT < 5000) THEN
   EXCEPTION EXP_INVALID_QUANTITY(NEW.FIREBIRD_ORDERS_QT, 'Firebird 
servers', '5,000');

regards
Marco Menardi


Dmitry Yemanov wrote:
> Nickolay,
> 
> 
>>>I think that this is discussion concerning 2.0 :)
>>
>>I think it is still possible to bribe Dmitry to implement this
>>feature in 1.5. ;))
> 
> 
> Sorry, but it's not problem for Dmitry to just write small SP in his
> databases to handle parameters in exception messages ;-)
> 
> 
> Dmitry
> 
> 
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Re: Re[2]: [Firebird-devel] Exceptions with custom message text

[Mike N. <ta...@al...>]

Nickolay Samofatov wrote:

> I think it is still possible to bribe Dmitry to implement this
> feature in 1.5. ;))

I don't think it should even be considered for 1.5, especially not this
late in the beta-stages. Shouldn't we have been at feature-freeze quite
some time ago?

> Mike, if you really need this feature

_I_ don't need it. I'm not even sure I'd want it! :-)

It was someone else that suggested the %s syntax. I just commented on
some of the technical aspects, possible problems and possible
solution(s) of such parameterized string  substitution.

/Mike