Issue using Dapper with C# to call an Oracle stored proc with refcursor as out parameter, however refcursor as return value works

Given this oracle stored proc package:

CREATE OR REPLACE 
PACKAGE TESTPKG AS 
  FUNCTION TestReturnRefCursor RETURN SYS_REFCURSOR;
  PROCEDURE TestingRefCursorsAsOutParam (outp OUT SYS_REFCURSOR);
END TESTPKG

And this package body:

CREATE OR REPLACE
PACKAGE BODY TESTPKG AS

  FUNCTION TestReturnRefCursor RETURN SYS_REFCURSOR AS
    outp SYS_REFCURSOR;
  BEGIN
    OPEN outp FOR SELECT * FROM TABLENAME;
    RETURN outp; 
  END TestReturnRefCursor;

  PROCEDURE TestingRefCursorsAsOutParam (outp OUT SYS_REFCURSOR) AS 
  BEGIN
    OPEN outp FOR SELECT * FROM TABLENAME;
  END TestingRefCursorsAsOutParam;

END TESTPKG;

I am trying to use Dapper to call either function. I have created the OracleDynamicParameters class that implements Dapper.SqlMapper.IDynamicParameters that I found at this post after searching StackOverflow: https://gist.github.com/vijaysg/3096151

Calling the TestReturnRefCursor stored function works fine with this code:

        var conn = new OracleConnection(ConfigurationManager.ConnectionStrings["DataConnection"].ConnectionString);
        conn.Open();
        var p = new OracleDynamicParameters();
        p.Add("retSet", dbType: OracleDbType.RefCursor, direction: ParameterDirection.ReturnValue);
        conn.Execute("TESTPKG.TestReturnRefCursor ", param: p, commandType: CommandType.StoredProcedure);
        var refcur = p.Get<OracleRefCursor>("retSet");
        // do something with refcur
        conn.Close();

However, when I try to call the TestingRefCursorsAsOutParam stored procedure with this code:

var conn = new OracleConnection(ConfigurationManager.ConnectionStrings["DataConnection"].ConnectionString);
conn.Open();
var p = new OracleDynamicParameters();
p.Add("retSet", dbType: OracleDbType.RefCursor, direction: ParameterDirection.Output);
conn.Execute("TESTPKG.TestingRefCursorsAsOutParam ", param: p, commandType: CommandType.StoredProcedure);
var refcur = p.Get<OracleRefCursor>("retSet");
// do something with refcur
conn.Close();

I get an OracleException from the Oracle.ManagedDataAccess.dll with the detail:

"ORA-06550: line 1, column 7:\nPLS-00306: wrong number or types of arguments in call to 'TESTINGREFCURSORSASOUTPARAM'\nORA-06550: line 1, column 7:\nPL/SQL: Statement ignored"

I found after searching another stackoverflow post where sometimes parameters aren't bound if they are null unless you specifically set their value to be DBNull.Value, so I tried changing the add parameter line to be:

p.Add("retSet", value: DBNull.Value, dbType: OracleDbType.RefCursor, direction: ParameterDirection.Output);

but this did not help.

I can call this stored procedure just fine using regular c# oracle code:

var cmd = conn.CreateCommand();
cmd.CommandText = "TESTPKG.TestingRefCursorsAsOutParam";
cmd.CommandType = CommandType.StoredProcedure;

var outparam = new OracleParameter();
outparam.ParameterName = "retSet";
outparam.Direction = ParameterDirection.Output;
outparam.OracleDbType = OracleDbType.RefCursor;

cmd.Parameters.Add(outparam);

OracleDataAdapter da = new OracleDataAdapter(cmd);
cmd.ExecuteNonQuery();

var refcur = (OracleRefCursor)cmd.Parameters[0].Value;

Is there something I am missing here, or is Dapper not functioning correctly?

If you do not want to use a strong type for your result using dapper (i.e: Query<YourStrongType> ), you can use Query<dynamic>, the code below should work:

 IEnumerable<dynamic> results = null;
 using (var conn = new OracleConnection(ConfigurationManager.ConnectionStrings["DataConnection"].ConnectionString))
{
    var p = new OracleDynamicParameters();
    p.Add("outp ", dbType: OracleDbType.RefCursor, direction: ParameterDirection.Output);
    results = conn.Query<dynamic>("TESTPKG.TestingRefCursorsAsOutParam", p, commandType: CommandType.StoredProcedure);

    foreach (var row in results)
    {
         var fields = row as IDictionary<string, object>;
    }
}