Re: Check constraint on foreign table using SQL function

On 25.12.2014 23:50, Adrian Klaver wrote:
> On 12/25/2014 11:21 AM, Andreas Ulbrich wrote:
>> Hey.
>>
>> In the first part I connect to testdb (the remote db). Here I create the
>> schema 'andreas'. That the search_path correct is, shows the output of
>> the pgplsql version.
>
> Yeah, that was a false alarm on my part. Forgot about $user in the path.
>>
>> Then, in the second part, I'm postgres (this db ist empty since
>> compiling).
>> The usermapping says, I wont to be andreas@testdb.
>> The plpgsql-version (and the other work arround: schema qualified, set
>> search_path) shows, that my assumptions are correct.
>>
>> First I'm wondering, why are the constraints are checked in select, but
>> this is not the main problem, because, if I would do an INSERT, I will
>> get the same problem.
>
> The issue seems to begin here:
>
> CREATE TABLE IF NOT EXISTS tab_b (
>      id INTEGER PRIMARY KEY,
>      id_a INTEGER NOT NULL REFERENCES tab_a,
>      name TEXT,
>      CHECK(test_name_b(id_a, name))
>    );
> The CHECK calls test_name_b() which has
>
> SELECT $2 = name FROM tab_a WHERE id = $1  in it
>
> As Tom said fdw calls have a limited search_path and the tab_b table
> is not schema qualified in the function, so:
>
> 2014-12-24 13:11:27 CET andreas(at)testdb QUERY:   SELECT $2 = name FROM
> tab_a WHERE id = $1
> 2014-12-24 13:11:27 CET postgres(at)postgres ERROR:  relation "tab_a"
> does
> not exist
> 2014-12-24 13:11:27 CET postgres(at)postgres CONTEXT:  Remote SQL
> command:
> SELECT id, id_a, name FROM andreas.tab_b
>          SQL function "test_name_b" during inlining
>
> As you found out you need to be explicit about your schemas when going
> through fdw. Either schema qualify object names of set explicit
> search_path,
>
> All this starts when you try to create the foreign table:
>
> 2014-12-24 13:11:27 CET postgres(at)postgres STATEMENT:  TABLE ftab_b;
>
>
>>
>> I believe, that the "inlining" does not use the search_path set in the
>> ALTER DATABASE.
>>
>> Here is a \d output before the END of the transaction in the first part.
>>                List of relations
>>   Schema  |   Name   |     Type      |  Owner
>> ---------+----------+---------------+---------
>>   andreas | tab_a    | table         | andreas
>>   andreas | tab_b    | table         | andreas
>>   test    | unaccent | foreign table | test
>>
>> Regards
>> Andreas
>>
>>
>
>
O.K. I've seen.
I tried again the plpgsql version:
1.) the INSERTS on testdb prints the correct search_path in the raise
WARNING:  test_name_b called: "$user", test, public, ext
2.) Here the TABLE ftab_B works; because the check constraint is not
done (the constraint function is not called)
Is there any deeper cause, why the check is done with SQL function and
not with plpgsql in SELECT? It seems not necessary to do the check - for me.
3.) Is I try to make an INSERT from postgres to testdb, it failes.
And here is the search path not set:
WARNING: test_name_b called: pg_catalog
I think, that's a gap in the fdw.

My idea was the following: I wont do some refactoring. So a created a
new DB with a new schema with the refactored data structure. To populate
this new structure I wanted to use fdw-select to the old structure. The
problem is, I can't do so much changes in the old structure. Further,
qualified table access in the function makes them not reuseable in the
new structure.

O.K. the new idea is. Create a new 'export' schema in the old DB with a
constraintless export formated tables (JSON), populate this in the old
DB and then use fdw to these special designed tables.

Thanks
Andreas