Question

Hi im trying to assign a default group to any user that registers with my site. Since the admin Id of that group is the administrator, I query my database for a group with a admin id of my administrator and then assign that group to the user. However the following error is being thrown
“Unable to cast object of type ‘System.Data.Objects.ObjectQuery`1[DatabaseModel1.Group]’ to type ‘DatabaseModel1.Group’. ”
Heres the code

        Dim defaultGroup = (From group As Group In context.Groups
                     Where group.AdminID = ((From users As User0 In context.User0
                                            Where users.Name Like "Administrator"
                                            Select users.UserID).First)
                       Select group)

        currentUser.Groups.Add(defaultGroup)//the error is being thrown here

any help would be appreciated
Thanks

Answer 1

It sounds like you’ve got a query which can return multiple results, but you’re trying to assign it to a single-value variable.

You probably just need to use something like:

currentUser.Groups.Add(defaultGroup.First)

The probable options are:

• First() – allows multiple results and returns the first; will throw an exception if there are none
• FirstOrDefault() – allows multiple results and returns the first; will return the default value for the element type (e.g. null) if there are no results
• Last() – allows multiple results and returns the last; will throw an exception if there are none
• LastOrDefault() – allows multiple results and returns the last; will return the default value for the element type (e.g. null) if there are no results
• Single() – expects exactly one result; if there are no results or mulitple results, an exception is thrown

Now that you’ve shown the query, it sounds like you should probably use a join rather than a nested query. I’m not hot on the VB query syntax, but in C# you might want:

var defaultGroupQuery = 
        from group in context.Groups
        join user in context.User0 on group.AdminID equals user.UserID
        where user.Name == "Administrator"
        select group;