Entity Framework POCO Serialization

Question

I will start to code a new Web application soon. The application will be built using ASP.Net MVC 3 and Entity Framework 4.1 (Database First approach). Instead of using the default EntityObject classes, I will create POCO classes using the ADO.NET POCO Entity Generator.

When I create POCOs using this tool, it automatically adds the Virtual keyword to all properties for change tracking and navigation properties for lazy loading.

I have however read and seen from demonstrations, that Julie Lerman (EF Guru!) seems to turn off lazy loading and also modifies her POCO template so that the Virtual keyword is removed from her POCO classes. Julie states the reason why she does this is because she is writing applications for WCF services and using the Virtual keyword with this causes a Serialization issue. She says, as an object is getting serialized, the serializer is touching the navigation properties which then triggers lazy loading, and before you know it you are pulling the whole database across the wire.

I think Julie was perhaps exagarating when she said this could pull the whole database across the wire, however, even so, this thought scares me!

My question is (finally), should I also remove the Virtual keyword from my POCO classes for my MVC application and use DectectChanges for my change tracking and Eager Loading to request navigation properties.

Your help with this would be greatly appreciated.

Thanks as ever.

Answer 1

Serialization can indeed trigger lazy loading because the getter of the navigation property doesn't have a way to detect if the caller is the serializer or user code.

This is not the only issue: whether you have virtual navigation properties or all properties as virtual EF will create a proxy type at runtime for your entities, therefore entity instances the serializer will have to deal with at runtime will typically be of a type different from the one you defined.

Julie's recommendations are the simplest and most reasonable way to deal with the issues, but if you still want to work with the capabilities of proxies most of the time and only sometimes serialize them with WCF, there are other workarounds available:

• You can use a DataContractResolver to map the proxy types to be serialized as the original types
• You can also turn off lazy loading only when you are about to serialize a graph

More details are contained in this blog post: http://blogs.msdn.com/b/adonet/archive/2010/01/05/poco-proxies-part-2-serializing-poco-proxies.aspx

Besides this, my recommendation would be that you use the DbContext template and not the POCO template. DbContext is the new API we released as part of EF 4.1 with the goal of providing greater productivity. It has several advantages like the fact that it will automatically perform DetectChanges so that you won't need in general to care about calling the method yourself. Also the POCO entities we generate for DbContext are simpler than the ones that we generate with the POCO templates. You should be able to find lots of MVC exampels using DbContext.

Answer 2

Well it depends on your need, if you are going to serialize your POCO classes than yes you should remove them (For example: when using WCF services or basically anything that will serialize your entire object). But if you are just building a web app that needs to access your classes than I would leave them in your classes as you control the objects that you will access in your classes through your code.