Hi.

I have a Silverlight Client which invokes a server method using InvokeServerMethodAsync from the Entity Manager.

This server methods returns the custom class "CustomWrapper", which has 3 properties: Description (string), ItemA, ItemB.  Both ItemA and ItemB are of type CustomEntity which belongs to my devforce model.

My issue here is that in the client callback the CustomEntity properties (ItemA and ItemB) are filled with detached entities.  I want to know the best way to attach these entities into my entity manager without getting exceptions like  "key already in the cache"

Right know, i have in my callback:

var tr = (CustomWrapper)args.Result; var ce= em.FindEntity(tr.ItemA.EntityAspect.EntityKey, true) as CustomEntity;  if (ce== null)   em.AttachEntity(tr.ItemA);

Keep in mind that ItemA may have navigation or relatedList properties filled with other entities, and using "AttachEntity" will cause the "already key in the cache" exception.  Do I have to go all the ItemA graph tree to check and add entities?

I don't want to use CacheStateManager to restore cache  from the server result, as I use the method  in other type of client(web) so don't really need it.

Regards,

Guillermo

 

I couldn't reproduce the issue.

Can you provide a reproducible test case?

 

Here's what I tried:

 

 

My returned employee has an Unchanged EntityState (and the orders as well).

 

Silvio.

 

I am attaching you an example project.

In the SL client, I want to attach both  TerritoryA and TerritoryB entities to the current manager.  Both entities are in unchanged state, but their EntityManager properties are set to NULL.     I have preloaded the Region entities before calling the server method (I have excluded region with id=1).   After calling the server method and getting its response in the Sl client,  TerritoryA has associated a region with id=1, so when attaching it to the current manager the exception is not thrown.  But, as TerritoryB has a region which is already in the entity manager's cache, when using Attach method the exception is thrown. 

 

In the sample you produced you get the exception because some entities already exist in cache.

Can you be more clear why you can't/don't want to use EntityCacheState? Sending ECS and merging it to the client's cache is the recommended way of doing this.

By sending the ECS back to the client you'd be sending only the queried entities around a wrapper. (the wrapper is not too much overhead)

 

I did, however, find an erratic behavior using AttachEntity where when attaching Territory (and the Included Region) the navigation between them is not completely resolved. I am further investigating the issue and will file a bug on the subject.

 

Silvio.

I am using the same method for a web application, where I don't want the entitycachestate, just my wrapper class back.

As in my SL client using my wrapper, is it considered "ok" to have entities in unchanged state but without entity manager assigned?  It is somehow confusing, these entities should have detached states.

Guillermo

 

That's one of the problems sending raw entities across the wire. (i.e. it "brings" its EntityState from the server)

Even in the event the entities come back to client with Detached EntityState (you can do that manually before sending them across the wire with EM.RemoveEntity(myEntity) ) you can still face the issue of trying to attach an already existing entity in the client's EM.

 

It's still unclear why not use ECS in your case. You mention "I am using the same method for a web application, where I don't want the entitycachestate, just my wrapper class back".

In this web app where you just want the wrapper class back, I assume you don't need to attach/integrate the entities to an EM.

In the other place you actually need to merge these entites into an EM, you most likely want to consider sending the ECS. (i.e. having 2 similar methods)

 

The reason I am insisting on using the ECS it because that's one of the reasons the ECS is there for. When you merge the retrieved ECS with the EM's, all the work of combining/fixing all entities/navigation properties is done behind the scenes for you.

If you insist in using AttachEntities, you'd have to do this work, i.e. ensuring you are not attaching an entity already present in the cache.

 

Silvio.

1.) The server method should return an object array of size 4.   One slot for the ECS and the other 3 for a list of entityKeys.  I could also use a wrapper class instead of the array.

2.) In SL client,  I would use InvokeServerMethodOperation's Result property, which contains the object array (indexes 0,1,2 are list of entityKeys; index 3 is the ECS), to restore the ECS into the EntityManager and, for each list of entityKeys, I would call EntityManager.FindEntity(EntityKey ek) so I can build up the  list of entities.  

Is there a better approach for this scenario?

 

That's definitely a better approach considering that retrieving entities by key is a far easier task than trying to attach entities that might or might not already be present in the EM.

 

Silvio.

I have some questions about this topic

1.- SBelini wrote "The reason I am insisting on using the ECS it because that's one of the reasons the ECS is there for", i think that the wiki should be suggest in the remote server topics that using ECS is the recomended way to return object results.

2.- How can i to return or send to/from remote server methods only the modified or new objects in the cache?

3.- resuming, how can i merge the results to the client cache without use ECS?

thanks.

2.  Well, you can use the ECS if you want, both to and from.  If not that, you can do a FindEntities to retrieve the entities wanted, and then pass them in a list or custom type.

3.  You can also use ImportEntities ( http://drc.ideablade.com/xwiki/bin/view/Documentation/entities-import - http://drc.ideablade.com/xwiki/bin/view/Documentation/entities-import ) or attach or add ( http://drc.ideablade.com/xwiki/bin/view/Documentation/entity-add-attach-remove - http://drc.ideablade.com/xwiki/bin/view/Documentation/entity-add-attach-remove ).

 

Do you have an example to the techniques suggested?