Thread: How to create a function with multiple RefCursor OUT parameters

How to create a function with multiple RefCursor OUT parameters

From

Chuck Bai

Date:

11 May 2008, 18:43:34

I have the following function:

CREATE OR REPLACE FUNCTION test_refcursor(INOUT tcount integer, OUT
o_user refcursor, OUT o_name refcursor)
  RETURNS record AS
$BODY$
BEGIN
    tcount := tcount + 1;
    OPEN o_user FOR SELECT * FROM user_table;
    OPEN o_name FOR SELECT * FROM name_table;
END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE

Question 1: The function is not working with Npgsql .NET data provider.
It did not return a valid .NET DataSet. But the INOUT parameter tcount
works fine. How could I test the above function with SQL in pgAdmin III?
I want to find out if problem is in the function or in the Npgsql.

Question 2: pgAdmin III automatically added "RETURNS record" in the
above function when RETURNS clause is not specified initially. Why is
that? Is this the problem since it returns only single data table with
the following value? How to fix it?

tcount     o_user     o_name
23     <unnamed portal 1>     <unnamed portal 2>


Question 3: I want to return a single DataSet with each OUT RefCursor
map to a DataTable within the DataSet,  plus extra OUT parameters for
individual OUT values. How could I create such a function?

Any help is appreciated.

Re: How to create a function with multiple RefCursor OUT parameters

From

"Merlin Moncure"

Date:

12 May 2008, 15:09:51

On Sun, May 11, 2008 at 2:43 PM, Chuck Bai <cbai22@gmail.com> wrote:
>  CREATE OR REPLACE FUNCTION test_refcursor(INOUT tcount integer, OUT o_user
> refcursor, OUT o_name refcursor)
>   RETURNS record AS
>  $BODY$
>  BEGIN
>    tcount := tcount + 1;
>    OPEN o_user FOR SELECT * FROM user_table;
>    OPEN o_name FOR SELECT * FROM name_table;
>  END;
>  $BODY$
>   LANGUAGE 'plpgsql' VOLATILE
>
>  Question 1: The function is not working with Npgsql .NET data provider. It
> did not return a valid .NET DataSet. But the INOUT parameter tcount works
> fine. How could I test the above function with SQL in pgAdmin III? I want to
> find out if problem is in the function or in the Npgsql.

You can test from pgAdmin by simply running queries in the query
window.  This sort of thing however might be a better fit for psql
(pasting your queries in the query window).  You need to use
transactions since refcursors only only good inside a transaction.

>  Question 2: pgAdmin III automatically added "RETURNS record" in the above
> function when RETURNS clause is not specified initially. Why is that? Is
> this the problem since it returns only single data table with the following
> value? How to fix it?

For a function with >1 out parameters, the output type is a record.
Your function returns (int, refcursor, refcursor) as defined.  SELECT
* FROM test_refcursor(7); would returns a row with three variables ( a
record).

>  tcount  o_user  o_name
>  23      <unnamed portal 1>      <unnamed portal 2>

You probably want to name your refcursors.  The way to do this is
simply o_user := 'something'; inside your pl/pgsql function.

-- inside pl/pgsql_function
refcur_variable := 'mycursor'

-- outside function, but in same transaction
FETCH ALL FROM mycursor -- or, "mycursor"

So, it would at least take a few 'queries' from the perppective of the
client to do what you are attempting.  However, all the data is 'set
up' for return to the client by the server in the main function.  The
server will hang on to it as long as the current transaction is valid
and then release it.

>
>
>  Question 3: I want to return a single DataSet with each OUT RefCursor map
> to a DataTable within the DataSet,  plus extra OUT parameters for individual
> OUT values. How could I create such a function?

Your question is a little opaque to me.  A refcursor is in PostgreSQL
terms a 'hande' to a set, not a DataTable the way you are
thinking...it's really a fancy string.  so, (INOUT int, OUT refcursor,
OUT refcursor) returns takes an 'int' in and returns an int and two
refcursors (strings), with extra work to return this to the client, at
least in terms of SQL statements.

I haven't used .net for a while but IIRC it's probably not possible to
'fill' multiple data tables in a single query without at least some
manual work.  Some of the npgsql experts might have some suggestions
however.  It really depends on how the code operates inside the npgsql
library.

merlin

Re: How to create a function with multiple RefCursor OUT parameters

From

Chuck Bai

Date:

13 May 2008, 02:29:18

The following is a function from PosgreSQL documentation to return
multiple cursors from a single function:

CREATE FUNCTION myfunc(refcursor, refcursor) RETURNS SETOF refcursor AS $$
BEGIN
    OPEN $1 FOR SELECT * FROM table_1;
    RETURN NEXT $1;
    OPEN $2 FOR SELECT * FROM table_2;
    RETURN NEXT $2;
END;
$$ LANGUAGE plpgsql;

-- need to be in a transaction to use cursors.
BEGIN;

SELECT * FROM myfunc('a', 'b');

FETCH ALL FROM a;
FETCH ALL FROM b;
COMMIT;


What I want to achieve is to modify the function to take an INOUT
parameter. For example:
myfunc(INOUT tcount integer, refcursor, refcursor). I want to add logic
to my INOUT parameter inside the function and return it back to client,
as well as returning the two refcursor results. How to modify this
function and how to test it in SQL to achieve my goal?

Merlin Moncure wrote:
> On Sun, May 11, 2008 at 2:43 PM, Chuck Bai <cbai22@gmail.com> wrote:
>
>>  CREATE OR REPLACE FUNCTION test_refcursor(INOUT tcount integer, OUT o_user
>> refcursor, OUT o_name refcursor)
>>   RETURNS record AS
>>  $BODY$
>>  BEGIN
>>    tcount := tcount + 1;
>>    OPEN o_user FOR SELECT * FROM user_table;
>>    OPEN o_name FOR SELECT * FROM name_table;
>>  END;
>>  $BODY$
>>   LANGUAGE 'plpgsql' VOLATILE
>>
>>  Question 1: The function is not working with Npgsql .NET data provider. It
>> did not return a valid .NET DataSet. But the INOUT parameter tcount works
>> fine. How could I test the above function with SQL in pgAdmin III? I want to
>> find out if problem is in the function or in the Npgsql.
>>
>
> You can test from pgAdmin by simply running queries in the query
> window.  This sort of thing however might be a better fit for psql
> (pasting your queries in the query window).  You need to use
> transactions since refcursors only only good inside a transaction.
>
>
>>  Question 2: pgAdmin III automatically added "RETURNS record" in the above
>> function when RETURNS clause is not specified initially. Why is that? Is
>> this the problem since it returns only single data table with the following
>> value? How to fix it?
>>
>
> For a function with >1 out parameters, the output type is a record.
> Your function returns (int, refcursor, refcursor) as defined.  SELECT
> * FROM test_refcursor(7); would returns a row with three variables ( a
> record).
>
>
>>  tcount  o_user  o_name
>>  23      <unnamed portal 1>      <unnamed portal 2>
>>
>
> You probably want to name your refcursors.  The way to do this is
> simply o_user := 'something'; inside your pl/pgsql function.
>
> -- inside pl/pgsql_function
> refcur_variable := 'mycursor'
>
> -- outside function, but in same transaction
> FETCH ALL FROM mycursor -- or, "mycursor"
>
> So, it would at least take a few 'queries' from the perppective of the
> client to do what you are attempting.  However, all the data is 'set
> up' for return to the client by the server in the main function.  The
> server will hang on to it as long as the current transaction is valid
> and then release it.
>
>
>>  Question 3: I want to return a single DataSet with each OUT RefCursor map
>> to a DataTable within the DataSet,  plus extra OUT parameters for individual
>> OUT values. How could I create such a function?
>>
>
> Your question is a little opaque to me.  A refcursor is in PostgreSQL
> terms a 'hande' to a set, not a DataTable the way you are
> thinking...it's really a fancy string.  so, (INOUT int, OUT refcursor,
> OUT refcursor) returns takes an 'int' in and returns an int and two
> refcursors (strings), with extra work to return this to the client, at
> least in terms of SQL statements.
>
> I haven't used .net for a while but IIRC it's probably not possible to
> 'fill' multiple data tables in a single query without at least some
> manual work.  Some of the npgsql experts might have some suggestions
> however.  It really depends on how the code operates inside the npgsql
> library.
>
> merlin
>
>

Re: How to create a function with multiple RefCursor OUT parameters

From

"Albe Laurenz *EXTERN*"

Date:

13 May 2008, 06:20:05

Chuck Bai wrote:
> I have the following function:
>
> CREATE OR REPLACE FUNCTION test_refcursor(INOUT tcount integer, OUT
> o_user refcursor, OUT o_name refcursor)
>   RETURNS record AS
> $BODY$
> BEGIN
>     tcount := tcount + 1;
>     OPEN o_user FOR SELECT * FROM user_table;
>     OPEN o_name FOR SELECT * FROM name_table;
> END;
> $BODY$
>   LANGUAGE 'plpgsql' VOLATILE
>
> Question 1: The function is not working with Npgsql .NET data provider.
> It did not return a valid .NET DataSet. But the INOUT parameter tcount
> works fine. How could I test the above function with SQL in pgAdmin III?
> I want to find out if problem is in the function or in the Npgsql.

psql is easier, but you can also issue SQL commands with pgAdmin III:

test=> BEGIN;
BEGIN
test=> SELECT * FROM test_refcursor(42);
 tcount |       o_user       |       o_name
--------+--------------------+--------------------
     43 | <unnamed portal 3> | <unnamed portal 4>
(1 row)

test=> FETCH ALL FROM "<unnamed portal 3>";
....
....
(n rows)

test=> FETCH ALL FROM "<unnamed portal 4>";
....
....
(m row)

test=> COMMIT;
COMMIT

So it looks to me like your funktion works well.

> Question 2: pgAdmin III automatically added "RETURNS record" in the
> above function when RETURNS clause is not specified initially. Why is
> that? Is this the problem since it returns only single data table with
> the following value? How to fix it?

It is unnecessary to have "RETURNS record", but it is not a problem.
It just means: "returns something".

You do not need to fix it.

> tcount     o_user     o_name
> 23     <unnamed portal 1>     <unnamed portal 2>
>
>
> Question 3: I want to return a single DataSet with each OUT RefCursor
> map to a DataTable within the DataSet,  plus extra OUT parameters for
> individual OUT values. How could I create such a function?

DataSet and DataTable ate .NET things, so you'd better ask on the Npgsql
forum.
What keeps you from adding extra OUT parameters?

Yours,
Laurenz Albe

Re: How to create a function with multiple RefCursor OUT parameters

From

Chuck Bai

Date:

16 May 2008, 02:55:57

Thank you Albe. I test your script using psql and it works as you found
out. If the function is correct. Now the problem is how to use the
function from client side. It could not use "<unnamed portal #>" kind of
thing from client. I tested the function using Npgsql connector and it
did not work. I got only thing like "43 | <unnamed portal 3> | <unnamed
portal 4>" returned as a single row to my .NET client. Any other clients
can use the function? Please advise.

Albe Laurenz *EXTERN* wrote:
> Chuck Bai wrote:
>
>> I have the following function:
>>
>> CREATE OR REPLACE FUNCTION test_refcursor(INOUT tcount integer, OUT
>> o_user refcursor, OUT o_name refcursor)
>>   RETURNS record AS
>> $BODY$
>> BEGIN
>>     tcount := tcount + 1;
>>     OPEN o_user FOR SELECT * FROM user_table;
>>     OPEN o_name FOR SELECT * FROM name_table;
>> END;
>> $BODY$
>>   LANGUAGE 'plpgsql' VOLATILE
>>
>> Question 1: The function is not working with Npgsql .NET data provider.
>> It did not return a valid .NET DataSet. But the INOUT parameter tcount
>> works fine. How could I test the above function with SQL in pgAdmin III?
>> I want to find out if problem is in the function or in the Npgsql.
>>
>
> psql is easier, but you can also issue SQL commands with pgAdmin III:
>
> test=> BEGIN;
> BEGIN
> test=> SELECT * FROM test_refcursor(42);
>  tcount |       o_user       |       o_name
> --------+--------------------+--------------------
>      43 | <unnamed portal 3> | <unnamed portal 4>
> (1 row)
>
> test=> FETCH ALL FROM "<unnamed portal 3>";
> ....
> ....
> (n rows)
>
> test=> FETCH ALL FROM "<unnamed portal 4>";
> ....
> ....
> (m row)
>
> test=> COMMIT;
> COMMIT
>
> So it looks to me like your funktion works well.
>
>
>> Question 2: pgAdmin III automatically added "RETURNS record" in the
>> above function when RETURNS clause is not specified initially. Why is
>> that? Is this the problem since it returns only single data table with
>> the following value? How to fix it?
>>
>
> It is unnecessary to have "RETURNS record", but it is not a problem.
> It just means: "returns something".
>
> You do not need to fix it.
>
>
>> tcount     o_user     o_name
>> 23     <unnamed portal 1>     <unnamed portal 2>
>>
>>
>> Question 3: I want to return a single DataSet with each OUT RefCursor
>> map to a DataTable within the DataSet,  plus extra OUT parameters for
>> individual OUT values. How could I create such a function?
>>
>
> DataSet and DataTable ate .NET things, so you'd better ask on the Npgsql
> forum.
> What keeps you from adding extra OUT parameters?
>
> Yours,
> Laurenz Albe
>
>

Re: How to create a function with multiple RefCursor OUT parameters

From

"Albe Laurenz"

Date:

16 May 2008, 07:36:04

Please don't top post!

Chuck Bai wrote:
>>> CREATE OR REPLACE FUNCTION test_refcursor(INOUT tcount integer, OUT
>>> o_user refcursor, OUT o_name refcursor)
>>>   RETURNS record AS
>>> $BODY$
>>> BEGIN
>>>     tcount := tcount + 1;
>>>     OPEN o_user FOR SELECT * FROM user_table;
>>>     OPEN o_name FOR SELECT * FROM name_table;
>>> END;
>>> $BODY$
>>>   LANGUAGE 'plpgsql' VOLATILE
>>>
>>> Question 1: The function is not working with Npgsql .NET data provider.
>>> It did not return a valid .NET DataSet. But the INOUT parameter tcount
>>> works fine. How could I test the above function with SQL in pgAdmin III?
>>> I want to find out if problem is in the function or in the Npgsql.
>>
>> psql is easier, but you can also issue SQL commands with pgAdmin III:
>>
>> test=> BEGIN;
>> BEGIN
>> test=> SELECT * FROM test_refcursor(42);
>>  tcount |       o_user       |       o_name
>> --------+--------------------+--------------------
>>      43 | <unnamed portal 3> | <unnamed portal 4>
>> (1 row)
>>
>> test=> FETCH ALL FROM "<unnamed portal 3>";
>> ....
>> ....
>> (n rows)
>>
>> test=> FETCH ALL FROM "<unnamed portal 4>";
>> ....
>> ....
>> (m row)
>>
>> test=> COMMIT;
>> COMMIT
>>
>> So it looks to me like your funktion works well.
>
> Thank you Albe. I test your script using psql and it works as you found
> out. If the function is correct. Now the problem is how to use the
> function from client side. It could not use "<unnamed portal #>" kind of
> thing from client. I tested the function using Npgsql connector and it
> did not work. I got only thing like "43 | <unnamed portal 3> | <unnamed
> portal 4>" returned as a single row to my .NET client. Any other clients
> can use the function? Please advise.

Easy as pie.

If you have trouble with unnamed cursors, name them:

CREATE OR REPLACE FUNCTION test_refcursor(INOUT tcount integer,
   OUT o_user refcursor, OUT o_name refcursor) RETURNS record AS
$BODY$
BEGIN
    o_user := 'o_user';
    o_name := 'o_name';
    tcount := tcount + 1;
    OPEN o_user FOR SELECT * FROM user_table;
    OPEN o_name FOR SELECT * FROM name_table;
END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE

Yours,
Laurenz Albe

Re: How to create a function with multiple RefCursor OUT parameters

From

"Merlin Moncure"

Date:

16 May 2008, 13:06:50

On Fri, May 16, 2008 at 2:17 AM, Albe Laurenz <laurenz.albe@wien.gv.at> wrote:
> Chuck Bai wrote:
> CREATE OR REPLACE FUNCTION test_refcursor(INOUT tcount integer,
>   OUT o_user refcursor, OUT o_name refcursor) RETURNS record AS
> $BODY$
> BEGIN
>    o_user := 'o_user';
>    o_name := 'o_name';
>    tcount := tcount + 1;
>    OPEN o_user FOR SELECT * FROM user_table;
>    OPEN o_name FOR SELECT * FROM name_table;
> END;
> $BODY$
>  LANGUAGE 'plpgsql' VOLATILE

also don't forget, the refcursors are only valid for the duration of
the transaction.

merlin

Re: How to create a function with multiple RefCursor OUT parameters

From

"Francisco Figueiredo Jr."

Date:

17 May 2008, 06:14:55

On Fri, May 16, 2008 at 10:06 AM, Merlin Moncure <mmoncure@gmail.com> wrote:
> On Fri, May 16, 2008 at 2:17 AM, Albe Laurenz <laurenz.albe@wien.gv.at> wrote:
>> Chuck Bai wrote:

Hi, Chuck!

What's the Npgsql code you are using to call this function?

Thanks in advance.

--
Regards,

Francisco Figueiredo Jr.
http://fxjr.blogspot.com
http://www.npgsql.org