c# asp.net: capture the raiserror() message from an SQL stored procedure

Question

I am trying to get my head around ASP.NET 4.0 using C# as my programming language of choice. I am a good SQL developer and so plan to do most of my business logic in SQL. The application will only interact with the database through stored procedures.

In the aspx page I have a datasource for populating a dataview which calls sp 'season_get_byID' and for the update 'season_update' which takes a number of parameters,

The aspx source shows

    <asp:SqlDataSource ID="dsDetail" runat="server" 
    ConnectionString="<%$ ConnectionStrings:ADR %>" 
        SelectCommand="season_get_by_ID" SelectCommandType="StoredProcedure" 
        UpdateCommand="season_Update" UpdateCommandType="StoredProcedure">
        <SelectParameters>
            <asp:ControlParameter ControlID="GridView1" Name="ID" 
        PropertyName="SelectedValue" Type="Int32" />
        </SelectParameters>
        <UpdateParameters>
            <asp:Parameter Name="ID" Type="Int32" />
            <asp:Parameter Name="Code" Type="String" />
            <asp:Parameter Name="Description" Type="String" />
            <asp:Parameter DbType="Datetime" Name="StartDate" />
            <asp:Parameter DbType="Datetime" Name="EndDate" />
            <asp:Parameter Name="isActive" Type="Byte" />
            <asp:Parameter Name="isCurrent" Type="Byte" />
        </UpdateParameters>
    </asp:SqlDataSource>

Where each asp:Parameter maps to an @Param argument in the stored procedure - so far so good

The stored proc does some validation before trying to do the update. If the validations fail then a RAISERROR(@errmsg,10,1) is raised.

What I can't work out is where in the aspx.cs code behind file I would try to capture the errors and what the syntax should be: should it be in the after_update event handler and if so it does not appear to be part of e.exception. I know that some of the validation in this routine could be done using the validation classes but this is a learning excercise in the manipulating the environment rather than final production code ie I am trying to understand what is possible, rather than what is 'correct'

text for stored proc is below.

ALTER Procedure [dbo].[season_Update] 
    (
        @ID int,
        @Code nvarchar(10), 
    @Description nvarchar(50), 
    @StartDate date, 
    @EndDate date, 
    @isActive tinyint, 
    @isCurrent tinyint
)
as
DECLARE @ERR nvarchar(max) = ''

IF (SELECT count(*) FROM season WHERE ID = @ID) = 0 
BEGIN
SET @ERR = @ERR + '|Season Doesn''''t exist'
END

/*validate that season code and description are not blank*/
IF (@Code is null 
or
ltrim(rtrim(@Code)) = ''
)
BEGIN
set @ERR =+ '|Season Code cannot be blank'
END

IF @ERR = ''
BEGIN
IF (@Description is null 
    or
    ltrim(rtrim(@Description)) = ''
    )
BEGIN
    set @ERR =+ '|Season Description cannot be blank'
END

/*validate that the season code does not already exist on a different ID*/
IF (SELECT count(*) FROM season WHERE Code = ltrim(rtrim(upper(@CODE))) and 
       ID <> @ID) > 0 
BEGIN
    SET @ERR =+ '|Season Code ' + @Code + 'already exists'
END

/*validate that the start date is before the end date*/
IF @Startdate > @Enddate
BEGIN
    SET @ERR =+ '|Start Date cannot be Before End Date'
END
END

IF @ERR = ''
BEGIN
BEGIN TRY
UPDATE Season
    SET Code = ltrim(rtrim(upper(@Code))), 
        Description = Ltrim(rtrim(@Description)), 
        StartDate = @StartDate, 
        EndDate = @EndDate, 
        isActive = @isActive, 
        isCurrent = @isCurrent
WHERE
        ID = @ID    
END TRY
BEGIN CATCH
RAISERROR(N'There was a problem',10,1)
END CATCH
END

IF @ERR <> ''
BEGIN
RAISERROR(@ERR,10,1)
END

Answer 1

Microsoft have an article on this, How to Retrieve Values in SQL Server Stored Procedures , albeit in Visual Basic. This should give you an idea on how to resolve your problem.