Question

I’m trying to serialize some objects with protobuf-net, but unfortunately they make liberal use of DateTimeOffset, which is not yet supported by protobuf-net. This leads to lots of:

No serializer defined for type: System.DateTimeOffset

Can I define my own serialization routine for unknown types? (The same question was asked earlier, but his problem was worked around.)

I’m using the latest protobuf-net beta, v2.0.0.431, under .NET 4 if it matters. I’m also using runtime definitions, so I have no way to declaratively specify how certain properties are to be handled.

Answer 1

There are two ways of approaching the issue of unknown “common” types; the first is to use a shim property, for example a property that represents the value as something similar (a string or long for example):

[ProtoMember(8)]
public string Foo {
    get { ... read from the other member ... }
    set { ... assign the other member ... }
}

The other approach is a surrogate, which is a second protobuf contract that is automatically substituted. The requirements to use a surrogate are:

• there must be a defined conversion operator (implicit or explict) between the two types (for example, DateTimeOffset and DateTimeOffsetSurrogate)
• you then use SetSurrogate(surrogateType) to educate protobuf-net, for example RuntimeTypeModel.Default.Add(typeof(DateTimeOffset), false).SetSurrogate(typeof(DateTimeOffsetSurrogate));

the shim property is simpler, but requires repeat per-member. The surrogate is applied automatically to all instances of the type within the model. The surrogate then follows standard protobuf-net rules, so you would indicate which members to serialize, etc.

EDIT: Adding code example

using System;
using ProtoBuf;

[ProtoContract]
public class DateTimeOffsetSurrogate
{
    [ProtoMember(1)]
    public string DateTimeString { get; set; }

    public static implicit operator DateTimeOffsetSurrogate(DateTimeOffset value)
    {
        return new DateTimeOffsetSurrogate {DateTimeString = value.ToString("u")};
    }

    public static implicit operator DateTimeOffset(DateTimeOffsetSurrogate value)
    {
        return DateTimeOffset.Parse(value.DateTimeString);
    }
}

Then register it like this

RuntimeTypeModel.Default.Add(typeof(DateTimeOffset), false).SetSurrogate(typeof(DateTimeOffsetSurrogate));