---

title: C# sidebar_position: 7 id: csharp license: | Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Output Layout

C# output is one .cs file per schema, for example:

• <csharp_out>/addressbook/Addressbook.cs

The C# model file name uses the normalized PascalCase source file stem. For example, service.fdl generates Service.cs, order-events.fdl generates OrderEvents.cs, and 123-schema.fdl generates Schema123Schema.cs.

Type Generation

Messages generate [ForyStruct] classes with C# properties and byte helpers:

[ForyStruct]
public sealed partial class Person
{
    public string Name { get; set; } = string.Empty;
    public int Id { get; set; }
    public List<Person.PhoneNumber> Phones { get; set; } = new();
    public Animal Pet { get; set; } = null!;

    public byte[] ToBytes() { ... }
    public static Person FromBytes(byte[] data) { ... }
}

Unions generate [ForyUnion] ADTs. Unknown(UnknownCase) is the Fory-provided forward-compatibility carrier marked with [ForyUnknownCase]. The marker only selects the carrier and does not add an entry to the schema case table. Schema-defined cases use non-negative [ForyCase] IDs. If a case needs non-default schema encoding, the generated [ForyCase] carries Type. Known case record names are PascalCase FDL case names; payload types are emitted as qualified references when needed to avoid name conflicts. A typed union must have at least one non-Unknown case.

[ForyUnion]
public abstract partial record Animal
{
    private Animal() {}

    [ForyUnknownCase]
    public sealed partial record Unknown(UnknownCase Value) : Animal;

    [ForyCase(0)]
    public sealed partial record Dog(global::addressbook.Dog Value) : Animal;

    [ForyCase(1)]
    public sealed partial record Cat(global::addressbook.Cat Value) : Animal;
}

Module Installation

Each schema generates a module class that installs imported modules first and then registers the local schema types:

public static class AddressbookForyModule
{
    public static void Install(Fory fory)
    {
        fory.Register<addressbook.Animal>((uint)106);
        fory.Register<addressbook.Person>((uint)100);
        // ...
    }
}

The C# model file basename and module class both use the normalized source file stem. They do not use csharp_namespace and they do not use gRPC service names. For example, service.fdl generates Service.cs and ServiceForyModule, while order-events.fdl generates OrderEvents.cs and OrderEventsForyModule. A gRPC service named Greeter generates the service companion GreeterGrpc.cs; it does not change the schema module name. To get GreeterForyModule, name the schema file greeter.fdl or Greeter.fdl.

This source-file rule lets several schemas target the same C# namespace without colliding. No namespace-derived or service-derived module alias is generated.

When explicit type IDs are not provided, generated installation uses computed numeric IDs (same behavior as other targets).

gRPC Service Companions

With --grpc, C# emits one <ServiceName>Grpc.cs per service. Its static service holder contains descriptors, <ServiceName>Base, <ServiceName>Client, and both BindService overloads. See C# gRPC for hosting, clients, dependencies, and streaming.