Using domains for case insensitivity
Hi all,
A while back I asked about creating a case insensitive postgresql. Tom,
at the time, suggested I create a case insensitive type instead.
I am now trying to go that route, and am wondering whether domains will
provide a shortcut for me. As far as I understand the task at hand, I am
quite capable of using all of the existing varchar functions for input,
output, storage, conversions and so on. The only thing I need to
override is the comparison functions (and the resulting index creation,
of course).
According to the docs, domains are not meant for that purpose, but for
changing constraints of a type. Is it possible to define a domain that
will have the same defaults and constraints as the base type, but will
have different comparison functions? Will that provide me with what I need?
Many thanks,
Shachar
--
Shachar Shemesh
Lingnu Open Source Consulting ltd.
http://www.lingnu.com/
Shachar Shemesh wrote:
According to the docs, domains are not meant for that purpose, but
for changing constraints of a type. Is it possible to define a domain
that will have the same defaults and constraints as the base type,
but will have different comparison functions? Will that provide me
with what I need?
Domains constrain the allowed values of a data type and nothing more.
If you were able to override operators, then you would create a new
data type, thus losing a fundamental property of domains. So this is
not the route you want to pursue.
Peter Eisentraut <peter_e@gmx.net> writes:
Shachar Shemesh wrote:
According to the docs, domains are not meant for that purpose, but
for changing constraints of a type. Is it possible to define a domain
that will have the same defaults and constraints as the base type,
but will have different comparison functions? Will that provide me
with what I need?
Domains constrain the allowed values of a data type and nothing more.
If you were able to override operators, then you would create a new
data type, thus losing a fundamental property of domains. So this is
not the route you want to pursue.
I agree. I think there are some cases where the function resolution
code would pick a function declared to take the domain as input, but
it'd be a chancy thing, because for all nontrivial cases the code first
flattens domains to base types.
You can make a separate type that just happens to use the same I/O
functions, and then create a binary-compatible cast to the old type to
allow free use of the existing operators. This is much more likely to
work reliably.
regards, tom lane