Question

Given the following classes,

public static void Test()
{
  var bigDictionary = new Dictionary<string, TestClass>();
  bigDictionary.Add("entry1", new TestClass());
  bigDictionary.Add("entry2", new TestClass());
  bigDictionary.Add("entry3", new TestClass());

  // EDIT: Added these lines
  bigDictionary["entry1"].MyDictionary.Add(1, new SecondTestClass() { MyVar = "hello" });
  bigDictionary["entry1"].MyDictionary.Add(2, new SecondTestClass() { MyVar = "world" });
  bigDictionary["entry2"].MyDictionary.Add(1, new SecondTestClass() { MyVar = "please" });
  bigDictionary["entry2"].MyDictionary.Add(2, new SecondTestClass() { MyVar = "work" });

  using (var file = System.IO.File.Create("test.temp"))
  {
    ProtoBuf.Serializer.Serialize(file, bigDictionary);
  }

  Dictionary<string, TestClass> outDict = null;
  using (var file = System.IO.File.OpenRead("test.temp"))
  {
    outDict = ProtoBuf.Serializer.Deserialize<Dictionary<string, TestClass>>(file);
  }

  // EDIT: You'll notice these asserts fail
  System.Diagnostics.Debug.Assert(outDict["entry1"].MyDictionary.ContainsKey(1));
  System.Diagnostics.Debug.Assert(outDict["entry1"].MyDictionary.ContainsKey(2));
  System.Diagnostics.Debug.Assert(outDict["entry2"].MyDictionary.ContainsKey(1));
  System.Diagnostics.Debug.Assert(outDict["entry2"].MyDictionary.ContainsKey(2));

}

[System.Runtime.Serialization.DataContract]
public class TestClass
{
  public TestClass()
  {
    MyDictionary = new Dictionary<int,SecondTestClass>();
  }

  [System.Runtime.Serialization.DataMember]
  public Dictionary<int, SecondTestClass> MyDictionary { get; set; }
}

[System.Runtime.Serialization.DataContract]
public class SecondTestClass
{
  [System.Runtime.Serialization.DataMember]
  public string MyVar { get; set; }
}

(How) can I get bigDictionary to serialize without throwing the following exception?

"Only data-contract classes (and lists/arrays of such) can be processed (error processing Dictionary`2)"

(I have tried tagging with DataContract/DataMember ProtoContract/ProtoMember etc. but nothing seems to work)

Thanks in advance for any help.

EDIT: Seems I have kinda worked it out. Given the above edited code, you’ll notice the asserts fail. So it would seem that the inner dictionary is not being serialized at all. However, if I change the DataContract tags to Protobuf.ProtoContract (and DataMember to ProtoMember), it correctly picks up the inner dictionary.

Am I mis-using the library or is this a bug?

Answer 1

The answer is that the exception being thrown was a little misleading, it was a serialization error of an object in the dictionary not the dictionary itself. The actual implementation I was dealing with was a little more complex than the example I gave, and as such had a variable of type object which was breaking it.