Question

In my .proto I have some messages that have optional fields. There is no native protogen for Debian so I don’t have one to experiment with (too lazy to compile it myself :).

Could you tell me how to implement an optional field in a class in C#? I would like to have a function or whatever that idicate the field is set (in C++ I have something like hasfoo() ). In examples I found in the internet there is nothing like that.

Answer 1

It supports a number of patterns here, to help transition from other serializers. And note that there are options in the protobuf-net protogen to include such members for you automatically.

Firstly, anything null is omitted; this includes both null references and Nullable<T> for structs. So:

[ProtoMember(1)]
public int? A {get;set;}

will behave.

Another option is default values; using .NET conventions:

[ProtoMember(2), DefaultValue(17)]
public int B {get;set;}

no values of 17 will be serialized.

For more explicit control, the ShouldSerialize* pattern (from XmlSerializer) and the *Specified pattern (from DataContractSerializer) are observed, so you can do:

[ProtoMember(3)]
public string C {get;set;}

public bool ShouldSerializeC() { /* return true to serialize */ }

and

[ProtoMember(4)]
public string D {get;set;}

public bool DSpecified {get;set;} /* return true to serialize */

These can be public or private (unless you are generating a standalone serialization assembly, which requires public).

If your main classes are coming from code-gen, then a partial class is an ideal extension point, i.e.

partial class SomeType {
    /* extra stuff here */
}

since you can add that in a separate code file.