Category BLL/UI Problem

mashour · November 25th, 2008, 05:06 PM

I'm following the code in the book, and have reached chapter 5, News and Article Management. Implementing the GridView/DetailsView in ManageCategories.aspx. I get the following exception when I try to update a category:

Code:

[InvalidOperationException: ObjectDataSource 'objCurrentCategory' could not find a non-generic method 'UpdateCategory' that has parameters: Title, Importance, ImageUrl, Description.]
   System.Web.UI.WebControls.ObjectDataSourceView.GetResolvedMethodData(Type type, String methodName, IDictionary allParameters, DataSourceOperation operation) +1440
   System.Web.UI.WebControls.ObjectDataSourceView.ExecuteUpdate(IDictionary keys, IDictionary values, IDictionary oldValues) +2292
   System.Web.UI.DataSourceView.Update(IDictionary keys, IDictionary values, IDictionary oldValues, DataSourceViewOperationCallback callback) +179
   System.Web.UI.WebControls.DetailsView.HandleUpdate(String commandArg, Boolean causesValidation) +1199
   System.Web.UI.WebControls.DetailsView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +545
   System.Web.UI.WebControls.DetailsView.OnBubbleEvent(Object source, EventArgs e) +163
   System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +56
   System.Web.UI.WebControls.DetailsViewRow.OnBubbleEvent(Object source, EventArgs e) +118
   System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +56
   System.Web.UI.WebControls.LinkButton.OnCommand(CommandEventArgs e) +106
   System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument) +175
   System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +31
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +32
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +244
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3836

I checked the method signature of MB.TheBeerHouse.BLL.Articles.Category.UpdateCatego ry() and it is the same as Marco's in the downloaded code.

Anybody have an idea of what could going wrong here?

Lee Dumond · November 25th, 2008, 05:26 PM

This is because UpdateCategory takes five parameters -- title, importance, description, imageUrl, and id.

If you don't pass the id, how would the database know which category to update, right? ;)

I suspect that you may have forgotten to specify DataKeyNames="ID" in the DetailsView.

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mashour · November 25th, 2008, 05:44 PM

It was exactly that. When I added the DataKeyNames attribute it worked just fine. I'm kinda fascinated by the magic of ASP.NET 2.0, especially with ObjectDataSources and how they automatically work with the GridView and DetailsView.

A couple of more questions on the code, though: Why are SortExpression attributes being used in the DetailsView? And I'm assuming that the InsertVisible attribute on BoundFields excludes them from the insertion operation. Am I correct?

Lee Dumond · November 25th, 2008, 06:25 PM

Quote:

quote:Originally posted by mashour
It was exactly that. When I added the DataKeyNames attribute it worked just fine. I'm kinda fascinated by the magic of ASP.NET 2.0, especially with ObjectDataSources and how they automatically work with the GridView and DetailsView.

That's reflection. The ObjectDataSource uses reflection on your type to figure out the method signatures at runtime. Pretty cool actually.

Quote:

quote:Originally posted by mashour

A couple of more questions on the code, though: Why are SortExpression attributes being used in the DetailsView? And I'm assuming that the InsertVisible attribute on BoundFields excludes them from the insertion operation. Am I correct?

Question 1: Very perceptive. SortExpressions are useful when you've implemented paging on your DetailsView. Since this doesn't apply here, the SortExpression property serves no purpose. But since they're usually added automatically when you configure the DetailsView in the designer, I suspect Marco just left them in there. No harm either way.

Question 2: InsertVisible="False" is used to indicate that you don't want a boundfield to show when the DetailsView is in Insert mode. It doesn't necessarily exclude a field from the insert operation, but it does prevent a user from supplying that data. Here, you wouldn't want the user to supply an ID (the database will do that) or the AddedBy (this field is set to the current user in code).

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mashour · November 25th, 2008, 06:32 PM

Thanks Lee!