Обсуждение: Getting my Database name in a C Extension

Hi,

I'm writing an extention (FDW), and I need, in my C code, the name of
my database ("contrib_regression_test" for example), and I've two
questions:

1) What is the easiest way to get that directly in C?

2) Is there a way to get this information in the SQL extension
installation/update scripts (like the @/extschema/@ substitution)?

Thanks,

Cedric

Cedric Berger <cedric@precidata.com> writes:
> I'm writing an extention (FDW), and I need, in my C code, the name of
> my database ("contrib_regression_test" for example), and I've two
> questions:

> 1) What is the easiest way to get that directly in C?

The usual locution is "get_database_name(MyDatabaseId)".

> 2) Is there a way to get this information in the SQL extension
> installation/update scripts (like the @/extschema/@ substitution)?

Nope.  Doesn't seem to me like a remarkably good idea to refer to it
in that sort of way anyway.  What would happen if someone renamed
the database after the extension is installed?

            regards, tom lane

On 02/10/14 18:13, Tom Lane wrote:

> Cedric Berger <cedric@precidata.com> writes:
>
>> 1) What is the easiest way to get that directly in C?
>
> The usual locution is "get_database_name(MyDatabaseId)".

Ok, but then how do I find "MyDatabaseId" in, say,
a BeginForeignScan() or GetForeignRelSize() FDW callback?

http://www.postgresql.org/docs/9.3/static/fdw-callbacks.html

Sorry for these beginner's questions, but I've trouble navigating
the documentation / source / examples for this kind of info.

PS: is "which see for additional details" really good English
in the fdw-callbacks.html documentation?

>> 2) Is there a way to get this information in the SQL extension
>> installation/update scripts (like the @/extschema/@ substitution)?
>
> Nope.  Doesn't seem to me like a remarkably good idea to refer to it
> in that sort of way anyway.  What would happen if someone renamed
> the database after the extension is installed?

Ok,
Make sense,

Thanks
Cedric

Cedric Berger wrote:
>>> 1) What is the easiest way to get that directly in C?
>>
>> The usual locution is "get_database_name(MyDatabaseId)".
> 
> Ok, but then how do I find "MyDatabaseId" in, say,
> a BeginForeignScan() or GetForeignRelSize() FDW callback?

It is a global, all you should have to do is
#include "miscadmin.h"

Yours,
Laurenz Albe

On 03/10/14 10:23, Michael Paquier wrote:

> On Fri, Oct 3, 2014 at 4:57 PM, Albe Laurenz <laurenz.albe@wien.gv.at
> <mailto:laurenz.albe@wien.gv.at>> wrote:
>  > Cedric Berger wrote:
>  >>>> 1) What is the easiest way to get that directly in C?
>  >>>
>  >>> The usual locution is "get_database_name(MyDatabaseId)".
>  >>
>  >> Ok, but then how do I find "MyDatabaseId" in, say,
>  >> a BeginForeignScan() or GetForeignRelSize() FDW callback?
>  >
>  > It is a global, all you should have to do is
>  > #include "miscadmin.h"
> When looking for a global variable, a command like that is generally useful:
> $ git grep MyDatabaseId -- *.h
> src/include/access/xact.h:      Oid                     dbId;
>          /* MyDatabaseId */
> src/include/miscadmin.h:extern PGDLLIMPORT Oid MyDatabaseId;

Thanks a lot!

I didn't think 'MyDatabaseId' was a real variable name...

Cedric