Expose a specific .net object as JSON

Question

I'm currently enabling JSON calls to my web services using the ScriptService attribute. The problem is that one of my classes references a second class and .Net is not picking up and writing out the JavaScript for the second class.

As a workaround I can write a dummy method that just returns the second class. Then .Net writes the JSON to allow it to be serialized. So in the following example:

[ScriptService]
public class MyService : WebService {
    [WebMethod]
    public void SaveClass1(Class1 class1) {
        ...
    }
}

[Serializable]
public class Class1 {
    public Class2 class2 { get; set; }
}

[Serializable]
public class Class2 {
}

MyService.asmx/js won't write code to allow me to instantiate Class2 in order for me to populate Class1. But I can make it work if I add:

[WebMethod]
public Class2 Dummy() {
    return new Class2();
}

to MyService. Any alternatives to my nasty workaround would be greatly appreciated.

Answer 1

Lee, not sure if this works in your JSON/[ScriptService] scenario, but to serialize an object graph in Searcharoo.net I used the System.Xml.Serialization.XmlInclude attribute on the 'base' class that I needed to serialize.

Basically this tells the XmlSerializer about Class2 so that it can be included in the Class1 serialization... kinda like an "opt-in" strategy for handling deep hierachies of objects.

You would add it like this (in your example):

[Serializable]
[System.Xml.Serialization.XmlInclude(typeof(Class2))]
public class Class1 {
    public Class2 class2 { get; set; }
}

...and then this

[WebMethod]
public void SaveClass1(Class1 class1) {
    ...
}

should return JSON with Class2 data inside Class1.

I did a quick google to find troubleshooting...XmlSerializer which might be a good read. HTH

Answer 2

You need to use System.Web.Script.Services.GenerateScriptTypeAttribute, which specifies that a server type should be included in the generated proxy code. You can apply this attribute to the web service itself or any method marked with WebMethodAttribute.

For example:

[ScriptService]
[GenerateScriptType(typeof(Class2))]
public class MyService : WebService {
    [WebMethod]
    public void SaveClass1(Class1 class1) {
        // ...
    }
}