Question

I am using LINQ-to-SQL for an application that queries a legacy database. I need to call a stored procedure, that selects a single integer value. Changing the stored procedure is not an option.

The designer creates a method with this signature:

private ISingleResult<sp_xal_seqnoResult> NextRowNumber([Parameter(DbType='Int')] System.Nullable<int> increment, [Parameter(DbType='Char(3)')] string dataset) 

I would like the return type to be int. How do I do this using LINQ-to-SQL ?

Answer 1

This would be trivial with a scalar function (UDF) rather than an SP. However, it should work easily enough – although if the SP is complex (i.e. FMT_ONLY can’t inspect it 100%) then you might need to ‘help’ it…

Here’s some dbml that I generated from a simplfied SP that returns an integer; you can edit the dbml via ‘open with… xml editor):

<Function Name='dbo.foo' Method='foo'>     <Parameter Name='inc' Type='System.Int32' DbType='Int' />     <Parameter Name='dataset' Type='System.String' DbType='VarChar(20)' />     <Return Type='System.Int32' /> </Function> 

(note you obviously need to tweak the names and data-types).

And here is the generated C#:

[Function(Name='dbo.foo')] public int foo([Parameter(DbType='Int')] System.Nullable<int> inc, [Parameter(DbType='VarChar(20)')] string dataset) {     IExecuteResult result = this.ExecuteMethodCall(this, ((MethodInfo)(MethodInfo.GetCurrentMethod())), inc, dataset);     return ((int)(result.ReturnValue)); } 

If your current SP uses SELECT (instead of RETURN), then the DBML will need to reflect this. You can fix this by hiding the implementation details, and providing a public wrapper in a partial class; for example:

<Function Name='dbo.foo' Method='FooPrivate' AccessModifier='Private'>     <Parameter Name='inc' Type='System.Int32' DbType='Int' />     <Parameter Name='dataset' Type='System.String' DbType='VarChar(20)' />     <ElementType Name='fooResult' AccessModifier='Internal'>       <Column Name='value' Type='System.Int32' DbType='Int NOT NULL' CanBeNull='false' />     </ElementType> </Function> 

The above describes an SP that returns a single table with a single column; but I’ve made the SP ‘private’ to the data-context, and the result-type ‘internal’ to the assembly (hiding it):

[Function(Name='dbo.foo')] private ISingleResult<fooResult> FooPrivate(     [Parameter(DbType='Int')] System.Nullable<int> inc,     [Parameter(DbType='VarChar(20)')] string dataset) {     IExecuteResult result = this.ExecuteMethodCall(this, ((MethodInfo)(MethodInfo.GetCurrentMethod())), inc, dataset);     return ((ISingleResult<fooResult>)(result.ReturnValue)); } 

Now in my own class file I can add a new partial class (a new .cs file) in the correct namespace, that exposes the method more conveniently:

namespace MyNamespace {     partial class MyDataContext     {         public int Foo(int? inc, string dataSet)         {             return FooPrivate(inc, dataSet).Single().value;         }     } } 

(the namespace and context names need to be the same as the actual data-context). This adds a public method that hides the grungy details from the caller.

Don’t edit the designer.cs file directly; your changes will be lost. Only edit either the dbml or partial classes.