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Queried my SQL database to fetch details into Dataset when converting the Datatable to Dataview by filtering, since being newbie to Linq, am receiving the basic conversion error.

Code:

DataView cktDv = (from clounceform in dsclounceForms.Tables["Table2"].AsEnumerable()
                                         where clounceform.Field<string>("Form_FileType_ID").Equals("5")
                                         select clounceform).CopyToDataTable().AsDataView();

Exception is

Unable to cast object of type 'System.Byte' to type 'System.String'.
System.Data.DataSetExtensions
at System.Data.DataRowExtensions.UnboxT`1.ReferenceField(Object value)
at System.Data.DataRowExtensions.Field[T](DataRow row, String columnName)
at ClounceFormsSuite.Design.CreateFormDesign.<>c.<CreateForm>b__12_0(DataRow bounceform) in myprojectfolderpath\CreateFormDesign.xaml.cs:line 115
at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
at System.Data.DataTableExtensions.LoadTableFromEnumerable[T](IEnumerable`1 source, DataTable table, Nullable`1 options, FillErrorEventHandler errorHandler)
at System.Data.DataTableExtensions.CopyToDataTable[T](IEnumerable`1 source)
at ClounceFormsSuite.Design.CreateFormDesign.CreateForm(String[] cktFileContent, String filePath, String formID) in myprojectfolderpath\CreateFormDesign.xaml.cs:line 114
at ClounceFormsSuite.Design.CreateFormDesign.UserControl_Loaded(Object sender, RoutedEventArgs e) in myprojectfolderpath\CreateFormDesign.xaml.cs:line 70

I couldnt proceed further i infact changed the casting of string to int and gives different error which is misleading me more When tried casting to int

DataView cktDataView = (from clounceform in dsclounceForms.Tables["Table2"].AsEnumerable()
                                         where clounceform.Field<int>("Form_FileType_ID") == 5
                                         select clounceform).CopyToDataTable().AsDataView();

error: 

 Specified cast is not valid.
timblistic
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1 Answers1

5

The data is a byte, not a string and not an int. Thus, you need to use Field<byte>(...):

I suspect this will work:

where clounceform.Field<byte>("Form_FileType_ID") == (byte)5
Marc Gravell
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  • It worked but why it is not working being an int datatype it is not converting when i cast it. – timblistic Jul 14 '16 at 10:55
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    @ArulManivannan because it **isn't** an `int`. You can't unbox things to something that they aren't. – Marc Gravell Jul 14 '16 at 10:59
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    @ArulManivannan: I can see why this confusing. It is not obvious why `int i = 5; byte b = (byte)i;` is legal whereas `object i = 5; byte b = (byte)i;` is not. The thing you are missing is that the cast operator uses one syntax for two very different operations. Eric Lippert's article, [Representation and identity](https://ericlippert.com/2009/03/03/representation-and-identity/), does an excellent job explaining the distinction. – Brian Jul 14 '16 at 17:32
  • @Brian, So glad to clear out my misunderstanding. Thanks. – timblistic Jul 15 '16 at 05:45