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.NET Forum / .NET Framework / New Users / July 2005Typed DataSet: "Cannot get value because it is DBNull": Why still using it?
Hi, Something I don't understand about a Typed DataSet: When a value in the DataSet is DBNull, it throws this error: "Cannot get value because it is DBNull". But aren't Typed DataSets invented to make life easier, to be able to get to tge Tables and Values with less code, in less time? But with this thing you need to add a Try-Catch around every statement when using the value, add for each value a default value in your DataSet (and you have to redo it each time something changes to your DataSet!), or don't allow Null-values in any of your Tables in your Sql Server.. So why are people still using these things? Did anybody find an easy, fast and good working solution to get around this problem? Pieter If the value in the dataset is null what do you expect the getter to return? How do you expect they will cast DBNull in, say, int? If you do not need/want nulls give the DataColumn a defaultvalue and set allowdbnull to false. You can also use the untyped indexer of the datarow which will return what is in the row regardless which type and wheather it is null or not. And one important thing: please do not crosspost, this is inpolite. Hope it helps. > Hi, > [quoted text clipped - 13 lines] > > Pieter Well, I expect it to return DBNull, and not an error! DBNull is actually also some kind of value, so throwing an exception isn't really a nice thing in my opinion, hehe :-) When using the Untyped DataSet it returns DBNull too, so i don't see a reason why they have changed this with a Typed DataSet... And yes indeed you can use the untyped indexer every time: but again: why use a Typed DataSet if you need to call everytime the untyped to read the value's? It jsut doesn't make any sense to me :-( Pieter PS: I didn't croospost this? I just send it to 4 newgroups that seem logically concerned to this: framework, adonet (it has something to do with it), vb (which I uses), general (because it happens in other languages too). But anyways my apologizes if I harmed anybody with this. > If the value in the dataset is null what do you expect the getter to return? > How do you expect they will cast DBNull in, say, int? If you do not [quoted text clipped - 28 lines] > > > > Pieter > Well, I expect it to return DBNull, and not an error! DBNull is actually > also some kind of value, so throwing an exception isn't really a nice thing > in my opinion, hehe :-) DBNull is a kind of value. But it is not convertible to int, string, or anything else. The declaration of the properties are that they return the types given. An example from one of my typed datasets: Public Property label As String Get Try Return CType(Me(Me.tableVariablepg.labelColumn),String) Catch e As InvalidCastException Throw New StrongTypingException( _ "Cannot get value because it is DBNull.", e) End Try End Get Set Me(Me.tableVariablepg.labelColumn) = value End Set End Property Now, if the label property must return a string, then you can't return DBNull.Value. Just try it in code - the compiler won't even let you. Insert "return dbnull.value" below the catch statement, and watch the nice wiggly blue line appear underneath it. > When using the Untyped DataSet it returns DBNull > too, so i don't see a reason why they have changed this with a Typed > DataSet... When you use an untyped dataset, it returns an Object type. When you use a typed dataset, it returns a type. Simple. What are you going to do in the code when the value is null? You're going to do something special. So why not check IsNull() beforehand anyway? Hi Dragu, Every nullable column in typed dataset has an Is[ColumnName]Null() method.  SignatureMiha Markic [MVP C#] - RightHand .NET consulting & development www.rthand.com Blog: http://cs.rthand.com/blogs/blog_with_righthand/ SLODUG - Slovene Developer Users Group www.codezone-si.info > Hi, > [quoted text clipped - 17 lines] > > Pieter Thanks! That solves my problem I guess :-) > Hi Dragu, > [quoted text clipped - 21 lines] > > > > Pieter Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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