Protobuf Source Generator

I have recently faced a challenge where significant amount of custom types had to be serializable with protobuf-net. A requirement for the task was to avoid attributing all properties with [ProtoMember]. A solution to this problem is using C# source generators to generate partial types with properties that are serializable. Such a source generator is described below and implemented in LaDeak.ProtobufSourceGenerator nuget package and GitHub project.

A source generator that generates partial helper classes where member properties are attributed with ProtoMember attribute for serialization with protobuf-net.

Getting Started

Install nuget package:

dotnet add package LaDeak.ProtobufSourceGenerator

The source generator creates partial classes with private properties that are attributed with [ProtoMember] attributes. The properties get and set a corresponding property from the source type. This way developers are free to add and remove properties without explicitly attributing them.

Note that adding, removing or reordering properties might cause breaking changes for the serialized data, as the tags assigned with [ProtoMember] attribute are given based on the source type's definition.

To generate a partial type for a custom type, mark the type with [ProtoContract] attribute and with partial modifier. For example, the following entity type can be made source generating:

public class Entity
    public int Id { get; set; }

Add [ProtoContract] attribute and partial modifier on the type definition:

public partial class Entity
    public int Id { get; set; }

With this change a corresponding partial type is generated, that can be used for serialization with protobuf-net:

#nullable enable
namespace SampleApp;
public partial class Entity
    private int ProtoId { get => Id; set => Id = value; }

The source generator generates serializable properties that are auto properties with getter and setters.

Non-Generating Properties

  • init properties are excluded from source generation

  • Non-auto properties are not generated

  • Properties marked with [ProtoIgnore] and [ProtoMemeber(x)] attributes are not generated.

  • Positional Records (not supported by protobuf-net)

In case a property needs to be serialized, but it has no corresponding generated property, it may be attributed with [ProtoMemeber(x)] on the original type. The source generator makes sure that tag x is not used on the generated partial type.

Nested Types

Generating partial types for nested types is supported, however parent types must be marked with partial modifier.


The source generator also comes with an analyzer helping source generation:

  • issues an error if a custom type of a property is not participating in source generation

  • issues an error if a source generated nested type's parent is not partial

  • issues an info if a property is not part of source generation