Wrapping Stored Procedures in .NET Languages

Posted by Jonathan Allen on Jun 03, 2009

Sections

Architecture & Design,

Development,

Operations & Infrastructure

Topics

.NET ,

Language Design ,

Data Access

Tags

C# 4 ,

C# ,

F# ,

VB 10 ,

.NET Framework 4.0 ,

Visual Basic.NET

Creating wrapper functions for pre-existing stored procedures is surprisingly difficult in .NET. Stored procedures have certain calling conventions that aren’t generally used in the .NET Framework. These include:

• Pass by Reference Parameters
• Output Parameters
• Optional Parameters with default values
• All parameters are nullable

Until recently, full mappings were not possible. C# doesn’t currently support optional parameters, making placeholders for missing parameters necessary. VB could handle optional parameters, but not if those parameters were also nullable. For example, you cannot write:

Function FindCustomer(Optional ByVal firstName As String = Nothing, _ 
                      Optional ByVal lastName As String = Nothing, _
                      Optional ByVal zipCode As Integer? = Nothing) As DataTable

 This becomes a real concern when call search-style stored procedures that then to have numerous optional parameters. With C# 4 and VB 10, the last of these holes have been addressed. C# now supports optional values and both languages can use optional types in conjunction with nullable structures.

Feature	C#	Mapping	VB	Mapping	F#	Mapping
Pass by Reference	1	ref type [param]	7	ByRef [param] As [type]	4	[param] : [type] byref
Output	1	out type [param]	7	ByRef [param] As [type]	4	[param] : [type] byref
Optional Strings	4	string param = [default]	7	Optional [param] As String = [default]	N/A 4	Normal functions do not support optional parameters. Method functions use: ?[param] : [type]
Optional (other)	4	[type] param = [default]	7	Optional param As [type] = [default]
Nullable Strings	1	string param	7	param as String	4	[param] : string [param] : string option
Nullable (other)	2	[type]? param	8	param As Nullable(of [type])	4	[param] : Nullable<[type]> [param] : [type] option
			9	param as [type]?
Optional Nullable (other)	4	[type]? param = [default]	10	Optional param As [type]? = [default]	4	?[param] : Nullable<[type]> ?[param] : [type] option

It should be noted that while F# does support returning multiple values, the support is very limited. There is no way to update more than one arbitrary mutable value without using the byref syntax.

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   Real .NET to Stored Procedure Implementation

   by Daniel Bullington

   I have successfully created a framework for mapping interface methods to database stored prcoedure calls, as part of my blog code suite.
   
   The framework is well engineered ans fully unit (in the true sense) tested.
   
   The code is at: www.codeplex.com/SoftwareIsHardwork
   Blog: blog.softwareishardwork.com
   
   For example:
   
   [DatabaseContract]
   public interface IMockDatabaseContract : IDisposable
   {
   [CommandContract(CommandType.StoredProcedure, "usp_DoSomething", CommandBehavior.Default, -1, false)]
   void DoSomething([ParameterContract(DbType.Int32, 0, "@ItemId")] int itemId);
   }
   
   would map to
   
   exec usp_DoSomething @ItemId
   
   but the .NET code ONLY sees the contract; a factory dishes out transparent prxoies which intercept these methods and do the real database work.
   
   Take a look...
   
   dpb
   
   D. P. Bullington

   Reply

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