Using a ref cursor in a .NET application v5.0.7.1

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A ref cursor is a cursor variable that contains a pointer to a query result set. The result set is determined by executing the OPEN FOR statement using the cursor variable. A cursor variable isn't tied to a particular query like a static cursor. You can open the same cursor variable a number of times with the OPEN FOR statement containing different queries and each time. A new result set is created for that query and made available by way of the cursor variable. You can declare a cursor variable in two ways:

  • Use the SYS_REFCURSOR built-in data type to declare a weakly typed ref cursor.
  • Define a strongly typed ref cursor that declares a variable of that type.

SYS_REFCURSOR is a ref cursor type that allows any result set to be associated with it. This is known as a weakly typed ref cursor. The following example is a declaration of a weakly typed ref cursor:

name SYS_REFCURSOR;

Following is an example of a strongly typed ref cursor:

TYPE <cursor_type_name> IS REF CURSOR RETURN emp%ROWTYPE;

Creating the stored procedure

The following sample code creates a stored procedure called refcur_inout_callee. It specifies the data type of the ref cursor being passed as an OUT parameter. To create the sample procedure, invoke EDB-PSQL and connect to the EDB Postgres Advanced Server host database. Enter the following SPL code at the command line:

CREATE OR REPLACE PROCEDURE
  refcur_inout_callee(v_refcur OUT SYS_REFCURSOR)
IS
BEGIN
   OPEN v_refcur FOR SELECT ename FROM emp;
END;

The following C# code uses the stored procedure to retrieve employee names from the emp table:

using System;
using System.Data;
using EnterpriseDB.EDBClient;
using System.Configuration;

namespace EDBRefCursor
{
    class EmpRefcursor
    {
        [STAThread]
        static void Main(string[] args)
        {
            string strConnectionString =
            ConfigurationManager.AppSettings["DB_CONN_STRING"];
            EDBConnection conn = new EDBConnection(strConnectionString);
            conn.Open();
            try
            {
                EDBTransaction tran = conn.BeginTransaction();
                EDBCommand command = new EDBCommand("refcur_inout_callee",
                    conn);
                command.CommandType = CommandType.StoredProcedure;
                command.Transaction = tran;
                command.Parameters.Add(new EDBParameter("refCursor",
                    EDBTypes.EDBDbType.Refcursor, 10, "refCursor",

                ParameterDirection.Output, false, 2, 2,
                    System.Data.DataRowVersion.Current, null));

                command.Prepare();
                command.Parameters[0].Value = null;

                command.ExecuteNonQuery();
                String cursorName = command.Parameters[0].Value.ToString();
                command.CommandText = "fetch all in \"" + cursorName + "\"";
                command.CommandType = CommandType.Text;

                EDBDataReader reader =
                    command.ExecuteReader(CommandBehavior.SequentialAccess);
                int fc = reader.FieldCount;
                while (reader.Read())
                {
                    for (int i = 0; i < fc; i++)
                    {
                        Console.WriteLine(reader.GetString(i));
                    }
                }
                reader.Close();
                tran.Commit();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message.ToString());
            }
        }
    }
}

The following .NET code snippet displays the result on the console:

for(int i = 0;i < fc; i++)
{
    Console.WriteLine(reader.GetString(i));
}

You must bind the EDBDbType.RefCursor type in EDBParameter() if you're using a ref cursor parameter.