Thread: Status of Fix Domain Casting TODO
I'm wondering if Gevik has had any time for further work on http://archives.postgresql.org/pgsql-hackers/2006-09/msg01738.php ? FWIW, I'm running into this trying to create a 'raw' domain that would automagically convert hex strings into actual binary data for storage in a bytea. My intention was to use that as the basis for an 'md5data' domain (unfortunately, calling the domain simply 'md5' results in a conflict with the built-in md5 function). So something to consider on the domain casting is the case of casting from domain A to domain B to a base type. -- Jim Nasby jim@nasby.net EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
"Jim C. Nasby" <jim@nasby.net> writes:
> FWIW, I'm running into this trying to create a 'raw' domain that would
> automagically convert hex strings into actual binary data for storage in
> a bytea.
I think you've got 0 chance of implementing that as a domain rather than
an independent type. Without or without revisions in the casting rules,
a domain has not got its own I/O functions, and never will.
regards, tom lane
Tom Lane wrote: > "Jim C. Nasby" <jim@nasby.net> writes: >> FWIW, I'm running into this trying to create a 'raw' domain that would >> automagically convert hex strings into actual binary data for storage in >> a bytea. > > I think you've got 0 chance of implementing that as a domain rather than > an independent type. Without or without revisions in the casting rules, > a domain has not got its own I/O functions, and never will. This might be less of an issue if we allowed such IO functions to be written in a loadable PL rather than in C. cheers andrew
On Mon, Jan 01, 2007 at 06:30:40PM -0600, Andrew Dunstan wrote: > Tom Lane wrote: > > "Jim C. Nasby" <jim@nasby.net> writes: > >> FWIW, I'm running into this trying to create a 'raw' domain that would > >> automagically convert hex strings into actual binary data for storage in > >> a bytea. > > > > I think you've got 0 chance of implementing that as a domain rather than > > an independent type. Without or without revisions in the casting rules, > > a domain has not got its own I/O functions, and never will. > > > This might be less of an issue if we allowed such IO functions to be > written in a loadable PL rather than in C. I'm confused... couldn't I just write a cast function? Or is that what's meant by I/O functions? And yes, in this case I should be able to accomplish what I'm looking for just using encode() and decode(). -- Jim Nasby jim@nasby.net EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
Jim C. Nasby wrote: > On Mon, Jan 01, 2007 at 06:30:40PM -0600, Andrew Dunstan wrote: > >> Tom Lane wrote: >> >>> "Jim C. Nasby" <jim@nasby.net> writes: >>> >>>> FWIW, I'm running into this trying to create a 'raw' domain that would >>>> automagically convert hex strings into actual binary data for storage in >>>> a bytea. >>>> >>> I think you've got 0 chance of implementing that as a domain rather than >>> an independent type. Without or without revisions in the casting rules, >>> a domain has not got its own I/O functions, and never will. >>> >> This might be less of an issue if we allowed such IO functions to be >> written in a loadable PL rather than in C. >> > > I'm confused... couldn't I just write a cast function? Or is that what's > meant by I/O functions? > > And yes, in this case I should be able to accomplish what I'm looking > for just using encode() and decode(). > The I/O functions are set up by the INPUT and OUTPUT params of the CREATE TYPE statement. They convert to and from the type 'cstring'. If you want to change the way a piece of data is read/produced (e.g. automatically encode/decode the value) these are what you would need. A domain is in effect a constrained type. But it inherits the I/O functions of its base type. But constraints are not what you want - you want to deal with representation, which is the property dealt with by I/O functions - their fundamental purpose is to convert between external and internal representation. HTH cheers andrew
On Tue, Jan 02, 2007 at 10:04:43AM -0500, Andrew Dunstan wrote: > Jim C. Nasby wrote: > >On Mon, Jan 01, 2007 at 06:30:40PM -0600, Andrew Dunstan wrote: > > > >>Tom Lane wrote: > >> > >>>"Jim C. Nasby" <jim@nasby.net> writes: > >>> > >>>>FWIW, I'm running into this trying to create a 'raw' domain that would > >>>>automagically convert hex strings into actual binary data for storage in > >>>>a bytea. > >>>> > >>>I think you've got 0 chance of implementing that as a domain rather than > >>>an independent type. Without or without revisions in the casting rules, > >>>a domain has not got its own I/O functions, and never will. > >>> > >>This might be less of an issue if we allowed such IO functions to be > >>written in a loadable PL rather than in C. > >> > > > >I'm confused... couldn't I just write a cast function? Or is that what's > >meant by I/O functions? > > > >And yes, in this case I should be able to accomplish what I'm looking > >for just using encode() and decode(). > > > > The I/O functions are set up by the INPUT and OUTPUT params of the > CREATE TYPE statement. They convert to and from the type 'cstring'. If > you want to change the way a piece of data is read/produced (e.g. > automatically encode/decode the value) these are what you would need. A > domain is in effect a constrained type. But it inherits the I/O > functions of its base type. But constraints are not what you want - you > want to deal with representation, which is the property dealt with by > I/O functions - their fundamental purpose is to convert between external > and internal representation. > You can fake out the input function by putting a check clause on the type definition. I agree there should be hooks allowing input/output functions to be written in pls. late to the thread, again, --elein