Where to perform immutable objects logic?

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Esko - 05 Oct 2005 21:59 GMT

A relatively simple question, I'd like to get some feedback from other
developers. Let's say I have the following a table with a list of countries,
which doesn't change (at least not very often). Now, in my table, I have the
list ordered alphabetically, however when I want to then query this table
from my application and display it on a jsp I want "USA" to list first,
followed by "Canada", then the rest of the countries. What I am doing at the
moment is grabbing the list from the db via JDBC into a Collection, then
removing both those entries, and then reinserting using List.add(pos,obj) at
positions 0 and 1, respectively. Should I be doing this in my app, or should
I do it at the database level? The options I have are to drop that table and
recreate it with the appropriate ordering, or change my select statement to
somehow put those two countries first (I'm not sure how to do that).

Any insight?

Thanks,

-Esko

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Oliver Wong - 05 Oct 2005 22:10 GMT

>A relatively simple question, I'd like to get some feedback from other
>developers. Let's say I have the following a table with a list of
[quoted text clipped - 11 lines]
>
> Any insight?

Disclaimer: I'm not sure that I have enough experience in relational
database design to make good design decision recommendations.

You could add an extra column, "favored" or "rank" or something like
that. Make USA's rank be 1, Canada's rank be 2, and all the other ranks be
NULL.

Then, in your SQL SELECT statement sort ascending first by rank, then by
country name. Hopefully NULL happens after 2 (can't recall off the top of my
head). If not, reverse the order of the sort, and swap the values of USA and
Canada (i.e. 2 and 1 respectively).

The benefit of this design is that you have a lot of freedom in grouping
the countries by giving countries in the same group equal rank (maybe list
USA, then Canada, then all the American countries (e.g. Mexico), then all
the european countries, and so on).

- Oliver

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Thomas G. Marshall - 06 Oct 2005 03:31 GMT

Oliver Wong coughed up:

>> A relatively simple question, I'd like to get some feedback from
>> other developers. Let's say I have the following a table with a list
[quoted text clipped - 29 lines]
>
> - Oliver

If what we're talking about amounts to a /GUI/ table (I'm not a db nor jsp
guy), then it would be relatively straightforward to create a Comparator
that handles the country names in a normal lexical fashion, but with the
quirk that USA and Canada sort at the top.

Such a comparator is likely to be useful in nearly /any/ sorting facility,
at least all the standard ones I can think of use it.

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Where to perform immutable objects logic?

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