Getting output buffer from DBMS_OUTPUT.GET_LINES in C#

Question

I'm trying to get the output from the DBMS_OUTPUT.PUT_LINE() method in my anonymous PL/SQL block through C#. I've looked at a couple of other related questions here, but am still having trouble. The return code of executing the anonymous block is returning -1, which should be correct based on the docs.

I'm setting the DBMS_OUTPUT.ENABLE() to NULL in order to not set a specific buffer size, then using the DBMS_OUTPUT.GET_LINES() method in order to get the lines from that buffer.

It returns nothing in the buffer (An empty OracleString[]) and returns 0 lines. My anonymous PL/SQL block is simple like this, but should work for any.

DECLARE
    lvsName VARCHAR2(6) := 'Oracle';
BEGIN
    DBMS_OUTPUT.PUT_LINE('Do you see me?');
    DBMS_OUTPUT.PUT_LINE('My name is: ' || lvsName);    
END;

What am I missing?

using (OracleDataAdapter oda = new OracleDataAdapter())
using (OracleCommand cmd = new OracleCommand(sql, _connection))
{
    // Execute anonymous PL/SQL block
    cmd.CommandType = CommandType.Text;
    var res = cmd.ExecuteNonQuery();

    // Set output Buffer
    cmd.CommandText = "BEGIN DBMS_OUTPUT.ENABLE(NULL); END;";
    cmd.CommandType = CommandType.Text;
    cmd.ExecuteNonQuery();

    // Get output
    cmd.CommandText = "BEGIN DBMS_OUTPUT.GET_LINES(:outString, :numLines); END;";
    cmd.CommandType = CommandType.Text;
    cmd.Parameters.Clear();
    cmd.Parameters.Add(new OracleParameter("outString", OracleDbType.Varchar2, int.MaxValue, ParameterDirection.Output));
    cmd.Parameters["outString"].CollectionType = OracleCollectionType.PLSQLAssociativeArray;
    cmd.Parameters["outString"].Size = sql.Length;
    cmd.Parameters["outString"].ArrayBindSize = new int[sql.Length];
    cmd.Parameters.Add(new OracleParameter("numLines", OracleDbType.Int32, ParameterDirection.InputOutput));
    cmd.Parameters["numLines"].Value = 10; // Get 10 lines
    cmd.ExecuteNonQuery();

     int numLines = Convert.ToInt32(cmd.Parameters["numLines"].Value.ToString());
     string outString = string.Empty;

     // Try to get more lines until there are zero left
     while (numLines > 0)
     {
         for (int i = 0; i < numLines; i++)
         {
             OracleString s = (OracleString)cmd.Parameters["outString"].Value;
             outString += s.ToString();
         }

         cmd.ExecuteNonQuery();
         numLines = Convert.ToInt32(cmd.Parameters["numLines"].Value.ToString());
     }

     return outString;
}

Answer 1

The main problem with your code was that it was not setting the bind size for each element of your output buffer. Also it was not properly indexing the output buffer when retrieving the results. And finally, the order of execution also plays a role: you have to first enable your output before executing your anonymous block of code. Every single change made is commented in the following MCVE. Only necessary changes to get it working were made.

static void Main(string[] args)
{
    string str = "User Id=xxx; password=xxx; Data Source=localhost:1521/xxx;";
    string sql = @"DECLARE lvsName VARCHAR2(6) := 'Oracle'; BEGIN  DBMS_OUTPUT.PUT_LINE('Do you see me?'); DBMS_OUTPUT.PUT_LINE('My name is: ' || lvsName); END;";

    OracleConnection _connection = new OracleConnection(str);

    try
    {
        _connection.Open();

        //adapter not being used
        //using (OracleDataAdapter oda = new OracleDataAdapter())

        using (OracleCommand cmd = new OracleCommand(sql, _connection))
        {
            // First enable buffer output
            // Set output Buffer
            cmd.CommandText = "BEGIN DBMS_OUTPUT.ENABLE(NULL); END;";
            cmd.CommandType = CommandType.Text;
            cmd.ExecuteNonQuery();

            // Then execute anonymous block
            // Execute anonymous PL/SQL block
            cmd.CommandText = sql;
            cmd.CommandType = CommandType.Text;
            var res = cmd.ExecuteNonQuery();


            // Get output
            cmd.CommandText = "BEGIN DBMS_OUTPUT.GET_LINES(:outString, :numLines); END;";
            cmd.CommandType = CommandType.Text;

            cmd.Parameters.Clear();

            cmd.Parameters.Add(new OracleParameter("outString", OracleDbType.Varchar2, int.MaxValue, ParameterDirection.Output));
            cmd.Parameters["outString"].CollectionType = OracleCollectionType.PLSQLAssociativeArray;
            cmd.Parameters["outString"].Size = sql.Length;
            cmd.Parameters["outString"].ArrayBindSize = new int[sql.Length];

            // set bind size for each array element
            for (int i = 0; i < sql.Length; i++)
            {
                cmd.Parameters["outString"].ArrayBindSize[i] = 32000;
            }


            cmd.Parameters.Add(new OracleParameter("numLines", OracleDbType.Int32, ParameterDirection.InputOutput));
            cmd.Parameters["numLines"].Value = 10; // Get 10 lines
            cmd.ExecuteNonQuery();

            int numLines = Convert.ToInt32(cmd.Parameters["numLines"].Value.ToString());
            string outString = string.Empty;

            // Try to get more lines until there are zero left
            while (numLines > 0)
            {
                for (int i = 0; i < numLines; i++)
                {
                    // use proper indexing here
                    //OracleString s = (OracleString)cmd.Parameters["outString"].Value;
                    OracleString s = ((OracleString[])cmd.Parameters["outString"].Value)[i];
                    outString += s.ToString();

                    // add new line just for formatting
                    outString += "\r\n";
                }

                cmd.ExecuteNonQuery();
                numLines = Convert.ToInt32(cmd.Parameters["numLines"].Value.ToString());
            }

            Console.WriteLine(outString);
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.ToString());
    }

    _connection.Close();
    _connection.Dispose();

    Console.WriteLine("Press RETURN to exit.");
    Console.ReadLine();
}

And the output result is:

Do you see me?
My name is: Oracle

Press RETURN to exit.

Answer 2

Thanks for the answer above by jsanalytics which provided a good basis for a solution. There are some issues with the above solution though, mostly having to do with the usage of sql.Length in many places where it doesn't make sense. Here is a reusable solution which corrects some of the issues.

using Oracle.DataAccess.Client;
using Oracle.DataAccess.Types;
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;

namespace MyNamespace
{
    public static class DbmsOutputHelper
    {
        public const int DefaultReadBatchSize = 10;

        public static void EnableDbmsOutput(this OracleConnection conn)
        {
            using (var cmd = conn.CreateCommand())
            {
                cmd.CommandText = "DBMS_OUTPUT.ENABLE";
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.ExecuteNonQuery();
            }
        }

        public static void DisableDbmsOutput(this OracleConnection conn)
        {
            using (var cmd = conn.CreateCommand())
            {
                cmd.CommandText = "DBMS_OUTPUT.DISABLE";
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.ExecuteNonQuery();
            }
        }

        public static List<string> ReadDbmsOutput(this OracleConnection conn, int readBatchSize = DefaultReadBatchSize)
        {
            if (readBatchSize <= 0)
            {
                throw new ArgumentOutOfRangeException(nameof(readBatchSize), "must be greater than zero");
            }

            using (var cmd = conn.CreateCommand())
            {
                cmd.CommandText = "DBMS_OUTPUT.GET_LINES";
                cmd.CommandType = CommandType.StoredProcedure;

                var linesParam = cmd.Parameters.Add(new OracleParameter("lines", OracleDbType.Varchar2, int.MaxValue, ParameterDirection.Output));
                linesParam.CollectionType = OracleCollectionType.PLSQLAssociativeArray;
                linesParam.Size = readBatchSize;
                linesParam.ArrayBindSize = Enumerable.Repeat(32767, readBatchSize).ToArray();   // set bind size for each array element

                var numLinesParam = cmd.Parameters.Add(new OracleParameter("numlines", OracleDbType.Int32, ParameterDirection.InputOutput));

                var result = new List<string>();
                int numLinesRead;

                do
                {
                    numLinesParam.Value = readBatchSize;
                    cmd.ExecuteNonQuery();
                    numLinesRead = ((OracleDecimal)numLinesParam.Value).ToInt32();

                    var values = (OracleString[])linesParam.Value;

                    for (int i = 0; i < numLinesRead; i++)
                    {
                        result.Add(values[i].ToString());
                    }

                } while (numLinesRead == readBatchSize);

                return result;
            }
        }
    }
}