Figure Out the Default Values of Stored Procedure Parameters

Introduction

When you are migrating a .NET application that uses ADO.NET to a Java-based one that uses JDBC, you will generally have to add code to add all the stored procedure parameters into the SqlCommand object, as the SQL JDBC doesn't allow you to 'ignore' parameters that have default values. In this article, you will see how you can derive all the parameters from a stored procedure using some T-SQL and C# code so that you can call your stored procedures and automatically have the default parameters assigned with their default values.

As SQL Server does not store the default values of stored procedure parameters in its system tables, and instead evaluates the text of the procedure at runtime, you lose some flexibility when writing applications that use T-SQL stored procedures. This problem can be worked around with a little bit of C# and some T-SQL. Get started using this T-SQL stored procedure called _GetAllProcedures:

CREATE PROCEDURE _GetAllProcedures 
AS 
SET NOCOUNT ON 
select sysobjects.name,syscolumns.name from sysobjects, syscolumns 
where 
sysobjects.xtype='P' and 
sysobjects.id = syscolumns.id 
RETURN 
GO

The C# code that will use this stored procedure to get all your stored procedures and evaluate them for their parameters is pretty straightforward. First, use two connections to the database � I will call these the 'main' connection, and the 'parameter' connection:

SqlConnection conSP = new SqlConnection(ConnectionString); 
SqlConnection conSPParamValue = 
    new SqlConnection(ConnectionString); 
conSP.Open(); 
conSPParamValue.Open();

Next, set up a SqlCommand on the main connection and initialize it with the stored procedure that you are interested in using:

SqlCommand cmdSP = new SqlCommand("_GetAllProcedures", conSP); 
cmdSP.CommandType = CommandType.StoredProcedure;

Next, the code will loop through the results of this stored procedure and ignore all of the system stored procedures that begin with the prefix 'dt_'. Trivia � 'dt' stands for 'DaVinci Tools' and the early code name for the technology used here to auto generate code when using the Enteprise Manager or design tools, so you could say that you've truly found the 'DaVinci Code'.

When the procedure isn't a 'dt_' one, you then create a new command on the 'params' connection to the '_GetParamDefault' stored procedure, which as its name suggests will get the default parameter for you:

string ParamDefaultValue = ""; 
SqlCommand cmdSPParamValue = 
    new SqlCommand("_GetParamDefault", conSPParamValue); 

cmdSPParamValue.CommandType = CommandType.StoredProcedure;

The code for this stored procedure is here:

CREATE proc _GetParamDefault
@Procname varchar(50),
@ProcParamName varchar(50),
@DefaultValue varchar(100) OUTPUT
as
/*
This procedure will return DEFAULT value for 
the parameter in thestored procedure.
Usage:
declare @Value varchar(30)
exec _GetParamDefault 'random_password','@password_type',
                                            @value OUTPUT
SELECT @VALUE

*****************************************************
Author: Eva Zadoyen
Edited: Rafael Mizrahi
*/

set nocount on
declare @sqlstr nvarchar(4000),
@obj_id int,
@version int,
@text varchar(8000),
@startPos int,
@endPos int,
@ParmDefinition NVARCHAR(500)
select @procName = rtrim(ltrim(@procname))
set @startPos= charindex(';',@Procname)

if @startPos<>0
begin
set @version = substring(@procname,@startPos +1,1)
set @procname = left(@procname,len(@procname)-2)
end
else
set @version = 1

SET @sqlstr =N'SELECT @text_OUT = (SELECT text FROM syscomments
WHERE id = object_id(@p_name) and colid=1 and number = @vers)'
SET @ParmDefinition = N'@p_name varchar(50),
@ParamName varchar (50),
@vers int,
@text_OUT varchar(4000) OUTPUT'

EXEC sp_executesql
@SQLStr,
@ParmDefinition,
@p_name = @procname,
@ParamName = @ProcParamName,
@vers = @version,
@text_OUT =@text OUTPUT

--select @TEXT

select @startPos = PATINDEX( '%' + @ProcParamName +'%',@text)
if @startPos<>0
begin
select @text = RIGHT ( @text, len(@text)-(@startPos +1))
select @endPos= CHARINDEX(char(10),@text) -- find the end of a line

select @text = LEFT(@text,@endPos-1)
-- check if there is a default assigned and 

-- parse the value to theoutput

select @startPos= PATINDEX('%=%',@text)
if @startPos <>0
begin
select @DefaultValue = 
     ltrim(rtrim(right(@text,len(@text)-(@startPos))))
select @endPos= CHARINDEX('--',@DefaultValue)
if @endPos <> 0
select @DefaultValue = rtrim(left(@DefaultValue,@endPos-1))

select @endPos= CHARINDEX(',',@DefaultValue)
if @endPos <> 0
select @DefaultValue = rtrim(left(@DefaultValue,@endPos-1))
end
ELSE
select @DefaultValue = 'NO DEFAULT SPECIFIED'
end
else
SET @DefaultValue = 'INVALID PARAM NAME'

set nocount off
return
GO

You then add parameters to this command, which are derived from the 'main' connection. These are the name of the procedure that you are currently inspecting and its parameter:

cmdSPParamValue.Parameters.Add("@Procname",
                             myReader.GetString(0));
cmdSPParamValue.Parameters.Add("@ProcParamName", 
                             myReader.GetString(1));

Finally, you specify the output type and execute the query:

SqlParameter param = cmdSPParamValue.Parameters.Add(
                    "@DefaultValue", SqlDbType.VarChar,100);
param.Direction = ParameterDirection.Output;
cmdSPParamValue.ExecuteNonQuery(); 
ParamDefaultValue = param.Value.ToString();

You now have the default value for the parameter, and you can use this in future calls to the stored procedure quite happily!

The full source code for this routine, in C# is shown below:

// open two connections 

string ConnectionString = "Data Source=localhost;Initial 
                           Catalog=Northwind;user id=sa"; 
SqlConnection conSP = new SqlConnection(ConnectionString); 
SqlConnection conSPParamValue = new SqlConnection(ConnectionString); 
conSP.Open(); 
conSPParamValue.Open(); 

// get all stored procedures and parameters 

SqlCommand cmdSP = new SqlCommand("_GetAllProcedures", conSP); 
cmdSP.CommandType = CommandType.StoredProcedure; 

// loop on all stored procecdures and parameters 

SqlDataReader myReader = cmdSP.ExecuteReader(); 
while (myReader.Read()) 
{ 
  if (myReader.GetString(0).ToLower().StartsWith("dt_") != true) 
  { 

    string ParamDefaultValue = ""; 
    SqlCommand cmdSPParamValue = new SqlCommand(
                         "_GetParamDefault", conSPParamValue); 
    cmdSPParamValue.CommandType = CommandType.StoredProcedure; 
    cmdSPParamValue.Parameters.Add("@Procname",
                               myReader.GetString(0)); 
    cmdSPParamValue.Parameters.Add(
             "@ProcParamName", myReader.GetString(1)); 

    SqlParameter param = cmdSPParamValue.Parameters.Add(
                         "@DefaultValue", SqlDbType.VarChar,100); 

    param.Direction = ParameterDirection.Output; 

    cmdSPParamValue.ExecuteNonQuery(); 

    ParamDefaultValue = param.Value.ToString(); 

    if (ParamDefaultValue != "NO DEFAULT SPECIFIED") 
    { 
      Console.WriteLine("{0}, {1}, {2}", myReader.GetString(0),    
                         myReader.GetString(1), ParamDefaultValue); 
    } 
  } 
} 
myReader.Close(); 
conSP.Close(); 
conSPParamValue.Close();

In this KB you have gained a new tool for your development toolbox: an automatic way of iterating through all the stored procedures in your database and extracting a list of their parameters that are declared with default values. With this list, you can then go through your code and find out where the stored procedures are used, and make sure that the SqlCommand is filled with all the parameters, including the optional ones.