On Fri, 20 May 2011 09:48:45 -0500,
Jack Christensen <jackc@hylesanderson.edu> wrote:
> On 5/20/2011 8:41 AM, Seb wrote:
>> Hi,
>> I'm trying to implementing the checking in and checking out of items
>> in a table, whereby an item cannot be checked out if it's not
>> checked-in. I've searched for schemas for public libraries where
>> this is a key requirement, but haven't managed to hit the right
>> keywords to get relevant results.
>> Thanks,
> Use a loans table with unique partial index to ensure that only one
> unreturned loan per item can exist at a time.
[...]
Thanks, this certainly avoids loaning an item before it's returned, but
it doesn't protect against having loans that overlap in time. For
example, an item can have a start_time that is between start_time and
end_time of a previous loan for that same item. My first thought was to
have some CHECK constraint with a query, but this doesn't seem to be
supported by postgresql.
--
Seb
