EF4 POCO WCF Serialization problems (no lazy loading, proxy/no proxy, circular references, etc)

Question

OK, I want to make sure I cover my situation and everything I've tried thoroughly. I'm pretty sure what I need/want can be done, but I haven't quite found the perfect combination for success.

I'm utilizing Entity Framework 4 RTM and its POCO support. I'm looking to query for an entity (Config) that contains a many-to-many relationship with another entity (App). I turn off lazy loading and disable proxy creation for the context and explicitly load the navigation property (either through .Include() or .LoadProperty()). However, when the navigation property is loaded (that is, Apps is loaded for a given Config), the App objects that were loaded already contain references to the Configs that have been brought to memory. This creates a circular reference.

Now I know the DataContractSerializer that WCF uses can handle circular references, by setting the preserveObjectReferences parameter to true. I've tried this with a couple of different attribute implementations I've found online. It is needed to prevent the "the object graph contains circular references and cannot be serialized" error. However, it doesn't prevent the serialization of the entire graph, back and forth between Config and App.

If I invoke it via WcfTestClient.exe, I get a stackoverflow (ha!) exception from the client and I'm hosed. I get different results from different invocation environments (C# unit test with a local reference to the web service appears to work ok though I still can drill back and forth between Configs and Apps endlessly, but calling it from a coldfusion environment only returns the first Config in the list and errors out on the others.) My main goal is to have a serialized representation of the graph I explicitly load from EF (ie: list of Configs, each with their Apps, but no App back to Config navigation.)

NOTE: I've also tried using the ProxyDataContractResolver technique and keeping the proxy creation enabled from my context. This blows up complaining about unknown types encountered. I read that the ProxyDataContractResolver didn't fully work in Beta2, but should work in RTM.

For some reference, here is roughly how I'm querying the data in the service:

var repo = BootStrapper.AppCtx["AppMeta.ConfigRepository"] as IRepository<Config>;
repo.DisableLazyLoading();
repo.DisableProxyCreation();

//var temp2 = repo.Include(cfg => cfg.Apps).Where(cfg => cfg.Environment.Equals(environment)).ToArray();
var temp2 = repo.FindAll(cfg => cfg.Environment.Equals(environment)).ToArray();
foreach (var cfg in temp2)
{
    repo.LoadProperty(cfg, c => c.Apps);
}

return temp2;

I think the crux of my problem is when loading up navigation properties for POCO objects from Entity Framework 4, it prepopulates navigation properties for objects already in memory. This in turn hoses up the WCF serialization, despite every effort made to properly handle circular references.

I know it's a lot of information, but it's really standing in my way of going forward with EF4/POCO in our system. I've found several articles and blogs touching upon these subjects, but for the life of me, I cannot resolve this issue. Feel free to simply ask questions and help me brainstorm this situation.

PS: For the sake of being thorough, I am injecting the WCF services using the HEAD build of Spring.NET for the fix to Spring.ServiceModel.Activation.ServiceHostFactory. However I don't think this is the source of the problem.

EDIT: The ProxyDataContractResolver class works correctly if I don't have the circular references. (i.e.: I make the setter of App.Configs to be private, which prevents serialization of the property.) It blows up, it appears, when it hits Configs via the App object -- they don't seem to be recognized as the same type as the top level Configs.

EDIT2: It appears that either EF or WCF doesn't recognize that the entities are indeed equal. i.e.: 'Config' is the same as a particular 'Config.Apps[x].Configs[y]'. The entity keys are properly set in the CSDL for each model and I've overridden the Equals() function to compare entities based on their 'Id' property. This fits the symptoms as no circular reference error is thrown, yet it is indeed a circular reference (and blows up WcfTestClient.exe) AND the ProxyDataContractResolver blows up when it hits the 'Config.Apps[x].Configs[y]' level of Configs. (It doesn't know how to map a Config proxy. The ProxyDataContractResolver works otherwise. It's like it knows how to handle the initial round of entities, but the second level it considers as different entities.)

Wow, I can be wordy. Sorry folks!

Answer 1

You might want to check out my blog post on this specific scenario - please email me if it doesn't help fix your current predicament! I've included a sample solution as well.

Please drop me some feedback either way, I'd really like to hear from more people on this particular issue - especially with the implementation problems on the client end of things.