EF 4 Self Tracking Entities does not work as expected

问题

I am using EF4 Self Tracking Entities (VS2010 Beta 2 CTP 2 plus new T4 generator). But when I try to update entity information it does not update to database as expected.

I setup 2 service calls. one for GetResource(int id) which return a resource object. the second call is SaveResource(Resource res); here is the code.

    public Resource GetResource(int id)
    {
        using (var dc = new MyEntities())
        {
            return dc.Resources.Where(d => d.ResourceId == id).SingleOrDefault();
        }        
    }

    public void SaveResource(Resource res)
    {
        using (var dc = new MyEntities())
        {
            dc.Resources.ApplyChanges(res);
            dc.SaveChanges();
            // Nothing save to database.
        }      
    }

    //Windows Console Client Calls
    var res = service.GetResource(1);
    res.Description = "New Change"; // Not updating...
    service.SaveResource(res); 

    // does not change anything.

It seems to me that ChangeTracker.State is always show as "Unchanged".

anything wrong in this code?

回答1:

This is probably a long shot... but:

I assume your Service is actually in another Tier? If you are testing in the same tier you will have problems.

Self Tracking Entities (STEs) don't record changes until when they are connected to an ObjectContext, the idea is that if they are connected to a ObjectContext it can record changes for them and there is no point doing the same work twice.

STEs start tracking once they are deserialized on the client using WCF, i.e. once they are materialized to a tier without an ObjectContext.

If you look through the generated code you should be able to see how to turn tracking on manually too.

Hope this helps

Alex

回答2:

You have to share assembly with STEs between client and service - that is the main point. Then when adding service reference make sure that "Reuse types in referenced assemblies" is checked.

The reason for this is that STEs contain logic which cannot be transfered by "Add service reference", so you have to share these types to have tracing logic on client as well.

回答3:

After reading the following tip from Daniel Simmons, the STE starts tracking. Here is the link for the full article. http://msdn.microsoft.com/en-us/magazine/ee335715.aspx

Make certain to reuse the Self-Tracking Entity template’s generated entity code on your client. If you use proxy code generated by Add Service Reference in Visual Studio or some other tool, things look right for the most part, but you will discover that the entities don’t actually keep track of their changes on the client.

so in the client make sure you don't use add service reference to get the proxy instead access service through following code.

var svc = new ChannelFactory<IMyService>("BasicHttpBinding_IMyService").CreateChannel();
var res = svc.GetResource(1);

回答4:

If you are using STEs without WCF you may have to call StartTracking() manually.

回答5:

I had the same exact problem and found the solution.

It appears that for the self-tracking entities to automatically start tracking, you need to reference your STE project before adding the service reference.

This way Visual Studio generates some .datasource files which does the final trick.

I found the solution here: http://blogs.u2u.be/diederik/post/2010/05/18/Self-Tracking-Entities-with-Validation-and-Tracking-State-Change-Notification.aspx

As for starting the tracking manually, it seems that you do not have these methods on the client-side.

Hope it helps...

来源：https://stackoverflow.com/questions/2166393/ef-4-self-tracking-entities-does-not-work-as-expected

标签

entity-framework

self-tracking-entities