如何检查输出 DbParameter 的空值？

Question

I'm using System.Data.Common.DbCommand.ExecuteNonQueryAsync to call an Oracle stored procedure that has one output parameter o_err_msg which (you guessed it) is a VARCHAR2 error message when an exception occurs or null when the procedure succeeds. So, after calling `ExecuteNonQueryAsync, I'm trying to check if that parameter is null, to see if there was an error or not. But can't find a way to actually do it.

I've tried comparing (through both the == operator and the Equals method) the Value property of the parameter to null, to DBNull.Value and calling System.Convert.IsDBNull on it. All of these return null. I've even tried converting it to string (either through the ToString method or System.Convert.ToString ) and then calling string.IsNullOrEmpty , but the resulting string is "null" .

The code I'm running is somewhat similar to this:

DbCommand cmd = dbConnection.CreateCommand();
cmd.CommandText = "PCKG_FOO.PROC_BAR";
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add(new OracleParameter("o_err_msg", OracleDbType.Varchar2, 4000, "", ParameterDirection.Output));

await cmd.ExecuteNonQueryAsync();

if (cmd.Parameters["o_err_msg"].Value != null)
    throw new InvalidOperationException(cmd.Parameters["o_err_msg"].Value.ToString());

Even though, in this example, I'm initializing the parameters as OracleParameter , in my code I only have DbParameter accessible and I'd prefer if I didn't have to cast it to OracleParameter or anything Oracle-specific.

Is there any way I can do this?

Thanks in advance.

Answer 1

I encountered the same problem today, the fowling code should be a workarround.

OracleParameter out1 = new OracleParameter("out1", OracleDbType.Varchar2, ParameterDirection.Output);
                out1.Size = 1000;
Oracle.ManagedDataAccess.Types.OracleString out1Value = (Oracle.ManagedDataAccess.Types.OracleString)out1.Value;
if (!out1Value.IsNull)
{
   // do something
}