Makiwa » ADO.NET http://www.makiwa.com Stuart Campbell's occasional musings about software development, etc. Thu, 08 May 2008 11:04:13 +0000 http://wordpress.org/?v=2.3.3 en Return value parameter returns null http://www.makiwa.com/index.php/2006/08/29/return-value-parameter-returns-null/ http://www.makiwa.com/index.php/2006/08/29/return-value-parameter-returns-null/#comments Tue, 29 Aug 2006 14:07:48 +0000 Stu http://www.makiwa.com/index.php/2006/08/29/return-value-parameter-returns-null/ I was really confused this morning. I was executing a stored proc that returned a single row of data, and a return value. However, the return value was always null - even though the stored proc ALWAYS returned a return value. The code was domething like this:

PLAIN TEXT
C#:
  1. SqlParameter retval = new SqlParameter("@RETURN_VALUE", SqlDbType.Int);
  2. retval.Direction = ParameterDirection.ReturnValue;
  3. command1.Parameters.Add(retval);
  4.  
  5. using (SqlDataReader reader = command1.ExecuteReader())
  6. {
  7.     if (reader.Read())
  8.     {
  9.         var1 = reader["Col1"].ToString();
  10.         var2 = reader["col2"].ToString();
  11.     }
  12.     if (retval.Value != null)
  13.         errorCode = Convert.ToInt32(retval.Value);
  14.     else
  15.         errorCode = -1;
  16. }

It turns out that you need to close the reader before you can access the return value parameter.
From MSDN Library: SqlDataReader.Close()

The Close method fills in the values for output parameters, return values and RecordsAffected...

I can see why it's been implemented like that (the return value, output parameters and number of records affected come at the end, after the result set) - but I have to say it is counter-intuitive to have to close the reader before you can access these values.

]]> http://www.makiwa.com/index.php/2006/08/29/return-value-parameter-returns-null/feed/ Enterprise Library Data Access and Stored Procedure Synonyms http://www.makiwa.com/index.php/2006/08/23/enterprise-library-data-access-and-stored-procedure-synonyms/ http://www.makiwa.com/index.php/2006/08/23/enterprise-library-data-access-and-stored-procedure-synonyms/#comments Tue, 22 Aug 2006 23:51:14 +0000 Stu http://www.makiwa.com/index.php/2006/08/23/enterprise-library-data-access-and-stored-procedure-synonyms/ The Enterprise Library Data Access application block offers some time-saving routines for calling stored procedures. However, they don't all work when the stored procedure is a synonym.

For example, once I have a Database object, I can get a DataReader from a stored proc called GetUser by simply calling:

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C#:
  1. Database db = DatabaseFactory.CreateDatabase();
  2. IDataReader reader = db.ExecuteReader("GetUser", userId);

However, if the stored procedure is a synonym I get an error:

System.InvalidOperationException : The stored procedure 'GetUser' doesn't exist.

The problem isn't actually the Enterprise Library. The problem is - as far as I can see - a bug in ADO.NET. It is the following call that fails:

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C#:
  1. SqlCommandBuilder.DeriveParameters((SqlCommand)discoveryCommand);

It seems to me that SqlCommandBuilder.DeriveParameters(SqlCommand command) hasn't been tested with the stored-proc-is-a-synonym scenario: the SQL that it uses to retrieve the parameters returns an empty result set.

I'm not too phased by this problem because I don't really like specifying the parameter values by ordinal position, which is what you're doing when you just supply a params object[] of values. So, I actually prefer using the workaround, which is to create the parameters explicitly:

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C#:
  1. Database db = DatabaseFactory.CreateDatabase();
  2. SqlCommand cmd = new SqlCommand("GetUser",
  3.     (SqlConnection)db.CreateConnection());
  4. cmd.CommandType = CommandType.StoredProcedure;
  5. db.AddInParameter(cmd, "@UserId", DbType.Int32, userId);
  6. IDataReader reader = db.ExecuteReader(cmd);

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