Question

I’m new to WCF RIA Services, and have been working with LightSwitch for 4 or so months now.
I created a generic screen to be used for editing lookup tables all over my LightSwitch application, mostly to learn how to create a generic screen that can be used with different entity sets on a dynamic basis.

The screen is pretty simple:

Opened with arguments similar to this:
Application.ShowLookupTypesList("StatusTypes", "StatusTypeId"); which correspond to the entity set for the lookup table in the database.

Here’s my WCF RIA service code:

using System.Data.Objects.DataClasses;
using System.Diagnostics;
using System.Reflection;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Data;
using System.Linq;
using System.ServiceModel.DomainServices.EntityFramework;
using System.ServiceModel.DomainServices.Server;

namespace WCF_RIA_Project
{
    public class LookupType
    {
        [Key]
        public int TypeId { get; set; }
        public string Name { get; set; }
    }

    public static class EntityInfo
    {
        public static Type Type;
        public static PropertyInfo Key;
        public static PropertyInfo Set;
    }

    public class WCF_RIA_Service : LinqToEntitiesDomainService<WCSEntities>
    {

        public IQueryable<LookupType> GetLookupTypesByEntitySet(string EntitySetName, string KeyName)
        {
            EntityInfo.Set = ObjectContext.GetType().GetProperty(EntitySetName);
            EntityInfo.Type = EntityInfo.Set.PropertyType.GetGenericArguments().First();
            EntityInfo.Key = EntityInfo.Type.GetProperty(KeyName);

            return GetTypes();
        }

        [Query(IsDefault = true)]
        public IQueryable<LookupType> GetTypes()
        {
            var set = (IEnumerable<EntityObject>)EntityInfo.Set.GetValue(ObjectContext, null);
            var types = from e in set
                        select new LookupType
                        {
                            TypeId = (int)EntityInfo.Key.GetValue(e, null),
                            Name = (string)EntityInfo.Type.GetProperty("Name").GetValue(e, null)
                        };
            return types.AsQueryable();
        }

        public void InsertLookupType(LookupType lookupType)
        {
            dynamic e = Activator.CreateInstance(EntityInfo.Type);
            EntityInfo.Key.SetValue(e, lookupType.TypeId, null);
            e.Name = lookupType.Name;

            dynamic set = EntityInfo.Set.GetValue(ObjectContext, null);
            set.AddObject(e);
        }

        public void UpdateLookupType(LookupType currentLookupType)
        {
            var set = (IEnumerable<EntityObject>)EntityInfo.Set.GetValue(ObjectContext, null);
            dynamic modified = set.FirstOrDefault(t => (int)EntityInfo.Key.GetValue(t, null) == currentLookupType.TypeId);
            modified.Name = currentLookupType.Name;
        }

        public void DeleteLookupType(LookupType lookupType)
        {
            var set = (IEnumerable<EntityObject>)EntityInfo.Set.GetValue(ObjectContext, null);
            var e = set.FirstOrDefault(t => (int)EntityInfo.Key.GetValue(t, null) == lookupType.TypeId);
            Debug.Assert(e.EntityState != EntityState.Detached, "Entity was in a detached state.");
            ObjectContext.ObjectStateManager.ChangeObjectState(e, EntityState.Deleted);
        }
    }
}

When I add an item to the list from the running screen, save it, then edit it and resave, I receive data conflict “Another user has deleted this record.”

I can workaround this by reloading the query after save, but it’s awkward.

If I remove, save, then readd and save an item with the same name I get unable to save data, “The context is already tracking a different entity with the same resource Uri.”

Both of these problems only affect my generic screen using WCF RIA Services. When I build a ListDetail screen for a specific database entity there are no problems. It seems I’m missing some logic, any ideas?

Answer 1

I’ve learned that this the wrong approach to using LightSwitch.

There are several behind-the-scenes things this generic screen won’t fully emulate and may not be do-able without quite a bit of work. The errors I’ve received are just one example. LightSwitch’s built-in conflict resolution will also fail.

LS’s RAD design means just creating a bunch of similar screens is the way to go, with some shared methods. If the actual layout needs changed across many identical screens at once, you can always find & replace the .lsml files if you’re careful and make backups first. Note that modifying these files directly isn’t supported.