Invalid cast from 'System.String' to 'System.Guid'

[Jonathan]

Hi, I'm sure there is a really simple answer to this, but...

I have a RadListBox bound to an OpenAccess datasource. The datasource is filtered on a querystring parameter, which is the string being passed to the parent form but the objects being retrieved use a GUID as the primary key and I get the error:

Invalid cast from 'System.String' to 'System.Guid'

Here is the definition for the datasource: 

<telerik:OpenAccessDataSource ID="OpenAccessDataSource2" runat="server" EnableDelete="False"
    EnableInsert="False" EnableUpdate="False" ObjectContextProvider="WorkProgramme.data.WPEntitiesModel, WorkProgramme.data"
    TypeName="WorkProgramme.data.ProjectDeliverable" Where="WpID == @WpID"
    OrderBy="ProjectDeliverableDescription">
    <WhereParameters>
        <asp:QueryStringParameter Name="WpID" QueryStringField="projectID" />
    </WhereParameters>
</telerik:OpenAccessDataSource>

Here is a portion of the stack trace:

[InvalidCastException: Invalid cast from 'System.String' to 'System.Guid'.]
   System.Convert.DefaultToType(IConvertible value, Type targetType, IFormatProvider provider) +9489160
   System.String.System.IConvertible.ToType(Type type, IFormatProvider provider) +8
   System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider) +9524264
   System.Convert.ChangeType(Object value, Type conversionType) +32
   Telerik.OpenAccess.RT.QueryImpl.Execute(Object[] args) +450
   Telerik.OpenAccess.RT.DataSource.OpenAccessDataSourceView.ExecuteOqlQuery(IQuery oqlQuery, Object[] queryArguments, Int32 startRowIndex, Int32 maximumRows) +136
   Telerik.OpenAccess.RT.DataSource.OpenAccessDataSourceView.ExecuteSelect(DataSourceSelectArguments arguments) +1386
   System.Web.UI.DataSourceView.Select(DataSourceSelectArguments arguments, DataSourceViewSelectCallback callback) +21
   Telerik.Web.UI.RadListBox.OnDataBinding(EventArgs e) +105
   Telerik.Web.UI.RadListBox.PerformSelect() +37

Any help would be appreciated.

Thanks,
Jonathan

[Zoran]

Hi Jonathan Simmons,

 Could you try adding the Type="System.Guid" and DbType="Guid" attributes to the parameter declaration? When the type of the parameter is not declared, the parameter is handled as a string one. I believe adding these two attributes should do the trick.

<asp:QueryStringParameter Name="WpID" QueryStringField="projectID" Type="System.Guid" DbType="Guid" />

Regards,
Zoran
the Telerik team

[Jonathan]

Hello Zoran,

This does not work as System.Guid does not exist in the list of options for Type and the page won't compile.

Cannot create an object of type 'System.TypeCode' from its string representation 'System.Guid' for the 'Type' property.

I have tried all the various combinations of Object, String and Guid but still cannot get this to work.

Regards,
Jonathan

[Jonathan]

Zoran,

With a little more fiddling I have managed to get this to work by:
- setting 'AutoGenerateWhereClause=True'
- setting 'DbType="Guid"'

Thanks,
Jonathan

[Zoran]

Hi Jonathan Simmons,

 I am glad to know that you have managed to get over this issue. Please, let me apologize for the glitch from my side, DbType is the only property that can be specified for Guid parameters, Type is valid only for certain types of parameters and you are right, Guid is not part of those. 

Kind regards,
Zoran
the Telerik team