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.
Community comments
Real .NET to Stored Procedure Implementation
by Daniel Bullington,
Real .NET to Stored Procedure Implementation
by Daniel Bullington,
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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