[web-devel] Database.Persistent

[Michael Snoyman]

That's interesting: I'd never considered the idea of inserting
undefined into fields you want excluded... That could work. The reason
I've avoided putting in this (often requested) feature is that I could
think of no way to do so and keep type safety. That might be an
approach.

We may consider requiring the user to supply the value instead,
thereby avoiding the library inserting undefined.

Michael

On Thu, May 5, 2011 at 4:32 PM, Greg Weber <greg at gregweber.info> wrote:
> An alternative to laziness would be selecting a subset of fields. There is
> no support for this directly in persistent, but it might be possible to add
> it and the future and have the value of an unselected field be something
> like undefined.
> At the moment you can select sub fields by dropping down to lower-level sql
> methods (ask Michael about these methods if you are interested). I think
> there is a technique for building your persistent data structure back up
> from the return of raw sql, which again you might be able to do by inserting
> dummy error fields.
> Greg Weber
>
> On Thu, May 5, 2011 at 4:18 AM, Michael Snoyman <michael at snoyman.com> wrote:
>>
>> On Thu, May 5, 2011 at 1:28 PM, Felipe Almeida Lessa
>> <felipe.lessa at gmail.com> wrote:
>> > On Thu, May 5, 2011 at 2:20 AM, Jeremy Hughes <jedahu at gmail.com> wrote:
>> >> Is Database.Persistent lazy wrt reading fields? I need to iterate over
>> >> entities containing both small and large fields. I do not need to use
>> >> the large fields in this instance, and so would rather they were not
>> >> read from the database.
>> >
>> > IIRC, they are read strictly.  I guess you should put them on a
>> > different entity.
>>
>> That's correct. In fact, Persistent avoids any form of lazy I/O to
>> ensure that database connections are returned to the pool as soon as
>> possible (amongst other reasons).
>>
>> Michael
>>
>> _______________________________________________
>> web-devel mailing list
>> web-devel at haskell.org
>> http://www.haskell.org/mailman/listinfo/web-devel
>
>