Preventing StackOverflowException while serializing Entity Framework object graph into Json

Question

I want to serialize an Entity Framework Self-Tracking Entities full object graph (parent + children in one to many relationships) into Json.

For serializing I use ServiceStack.JsonSerializer.

This is how my database looks like (for simplicity, I dropped all irrelevant fields):

I fetch a full profile graph in this way:

public Profile GetUserProfile(Guid userID)
{
    using (var db = new AcmeEntities())
    {
        return db.Profiles.Include("ProfileImages").Single(p => p.UserId == userId);
    }
}

The problem is that attempting to serialize it:

Profile profile = GetUserProfile(userId);
ServiceStack.JsonSerializer.SerializeToString(profile);

produces a StackOverflowException. I believe that this is because EF provides an infinite model that screws the serializer up. That is, I can techincally call: profile.ProfileImages[0].Profile.ProfileImages[0].Profile ... and so on.

How can I "flatten" my EF object graph or otherwise prevent ServiceStack.JsonSerializer from running into stack overflow situation?

Note: I don't want to project my object into an anonymous type (like these suggestions) because that would introduce a very long and hard-to-maintain fragment of code).

Answer 1

You have conflicting concerns, the EF model is optimized for storing your data model in an RDBMS, and not for serialization - which is what role having separate DTOs would play. Otherwise your clients will be binded to your Database where every change on your data model has the potential to break your existing service clients.

With that said, the right thing to do would be to maintain separate DTOs that you map to which defines the desired shape (aka wireformat) that you want the models to look like from the outside world.

ServiceStack.Common includes built-in mapping functions (i.e. TranslateTo/PopulateFrom) that simplifies mapping entities to DTOs and vice-versa. Here's an example showing this:

https://groups.google.com/d/msg/servicestack/BF-egdVm3M8/0DXLIeDoVJEJ

The alternative is to decorate the fields you want to serialize on your Data Model with [DataContract] / [DataMember] fields. Any properties not attributed with [DataMember] wont be serialized - so you would use this to hide the cyclical references which are causing the StackOverflowException.

Answer 2

For the sake of my fellow StackOverflowers that get into this question, I'll explain what I eventually did:

In the case I described, you have to use the standard .NET serializer (rather than ServiceStack's): System.Web.Script.Serialization.JavaScriptSerializer. The reason is that you can decorate navigation properties you don't want the serializer to handle in a [ScriptIgnore] attribute.

By the way, you can still use ServiceStack.JsonSerializer for deserializing - it's faster than .NET's and you don't have the StackOverflowException issues I asked this question about.

The other problem is how to get the Self-Tracking Entities to decorate relevant navigation properties with [ScriptIgnore].

Explanation: Without [ScriptIgnore], serializing (using .NET Javascript serializer) will also raise an exception, about circular references (similar to the issue that raises StackOverflowException in ServiceStack). We need to eliminate the circularity, and this is done using [ScriptIgnore].

So I edited the .TT file that came with ADO.NET Self-Tracking Entity Generator Template and set it to contain [ScriptIgnore] in relevant places (if someone will want the code diff, write me a comment). Some say that it's a bad practice to edit these "external", not-meant-to-be-edited files, but heck - it solves the problem, and it's the only way that doesn't force me to re-architect my whole application (use POCOs instead of STEs, use DTOs for everything etc.)

@mythz: I don't absolutely agree with your argue about using DTOs - see me comments to your answer. I really appreciate your enormous efforts building ServiceStack (all of the modules!) and making it free to use and open-source. I just encourage you to either respect [ScriptIgnore] attribute in your text serializers or come up with an attribute of yours. Else, even if one actually can use DTOs, they can't add navigation properties from a child object back to a parent one because they'll get a StackOverflowException. I do mark your answer as "accepted" because after all, it helped me finding my way in this issue.

Answer 3

Be sure to Detach entity from ObjectContext before Serializing it.

I also used Newton JsonSerializer.

JsonConvert.SerializeObject(EntityObject, Formatting.Indented, new JsonSerializerSettings { PreserveReferencesHandling = PreserveReferencesHandling.Objects });