ASP.NET MVC: JSON and a generic dictionary

If you attempt to convert a generic dictionary to JSON – with keys that are not strings nor objects, you will get an error message similar to:

‘System.Collections.Generic.Dictionary`2[[System.Int64, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]’ is not supported for serialization/deserialization of a dictionary, keys must be strings or objects.

This is a runtime error, i.e. the application will compile just fine. This is an ASP.NET MVC limitation, probably existing because in JavaScript, array keys can only be strings (foo[“bar”] = “fubar”).

I wrote a simple extension method – it simply turns your dictionary into Dictionary<string, object> using the default .ToString() method – so if you are using a complex data structure as your keys, remember to override the .ToString() method.

public static Dictionary<string, object> ToJsonDictionary<TKey, TValue>(this Dictionary<TKey, TValue> input)
{
	var output = new Dictionary<string, object>(input.Count);
	foreach (KeyValuePair<TKey, TValue> pair in input)			
		output.Add(pair.Key.ToString(), pair.Value);
	return output;
}  

Using the method is, of course, as easy as return Json(myDictionary.ToJsonDictionary());.

Generic Dictionary.AddRange() extension method.

In addition, another extension method.

For some reason, generic dictionary has gotten very little developer love from the creators of .NET, which is strange – dictionaries are one of the most widely used data structures together with the lists. Dictionaries cannot be serialized, they lack many useful methods – and one of the methods I’ve missed most is .AddRange(), ie. adding one dictionary to another.

So, another extension method:

public static void AddRange<TKey, TValue>(this Dictionary<TKey, TValue> input, Dictionary<TKey, TValue> addValues)
{
	foreach (KeyValuePair<TKey, TValue> pair in addValues)			
		input.Add(pair.Key, pair.Value);			
}

And that’s all. Simple, wasn’t it?

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