AvroSourceGenerator 0.1.1

Avro Source Generator

Avro Source Generator is a .NET source generator that generates C# code from Avro schemas and is compatible with Apache Avro.

It produces models that use modern C# features, such as nullable reference types, init-only properties, required properties, and more.

Prerequisites

• .NET SDK 8.0 or later

Usage

To use the Avro Source Generator in your project, add a reference to the AvroSourceGenerator package in your .csproj file:

dotnet add package AvroSourceGenerator

You can mark the AvroSourceGenerator package as PrivateAssets="all" to prevent projects referencing yours from getting a reference to it. Additionally, use ExcludeAssets="runtime" to ensure that AvroSourceGenerator.Attributes is not copied to the build output, since it is not required at runtime.

<PackageReference Include="AvroSourceGenerator" Version="*" PrivateAssets="all" ExcludeAssets="runtime" />

Then, configure the .csproj to include Avro schema files as AdditionalFiles.

<ItemGroup>
  <AdditionalFiles Include="schemas/*.avsc" />
</ItemGroup>

Add the schema file to the schemas folder in your project.

schemas/user.avsc

{
  "type": "record",
  "name": "User",
  "namespace": "example",
  "fields": [
    {
      "name": "Name",
      "type": "string"
    },
    {
      "name": "Email",
      "type": [
          "null",
          "string"
      ]
    },
    {
      "name": "CreatedAt",
      "type": {
          "type": "long",
          "logicalType": "timestamp-millis"
      }
    }
  ]
}

This will generate the C# files containing the types defined in the Avro schema.

Here is an example of a generated class for the User schema defined above:

// <auto-generated/>
#pragma warning disable CS8618, CS8633, CS8714, CS8775, CS8981
#nullable enable
namespace example
{
    [global::System.CodeDom.Compiler.GeneratedCode("AvroSourceGenerator", "1.0.0.0")]
    public partial record User : global::Avro.Specific.ISpecificRecord
    {
        public required string Name { get; init; }
        public string? Email { get; init; }
        public required global::System.DateTime CreatedAt { get; init; }
    
        public global::Avro.Schema Schema { get => User._SCHEMA; }
        public static readonly global::Avro.Schema _SCHEMA = global::Avro.Schema.Parse("""
        {
          "type": "record",
          "name": "User",
          "namespace": "example",
          "fields": [
            {
              "name": "Name",
              "type": "string"
            },
            {
              "name": "Email",
              "type": [
                "null",
                "string"
              ]
            },
            {
              "name": "CreatedAt",
              "type": {
                "type": "long",
                "logicalType": "timestamp-millis"
              }
            }
          ]
        }
        """);
    
        public object? Get(int fieldPos)
        {
            switch (fieldPos)
            {
                case 0: return this.Name;
                case 1: return this.Email;
                case 2: return this.CreatedAt;
                default: throw new global::Avro.AvroRuntimeException($"Bad index {fieldPos} in Get()");
            }
        }
        
        public void Put(int fieldPos, object? fieldValue)
        {
            switch (fieldPos)
            {
                case 0:
                    Set_Name(this, (string)fieldValue!); break;
                    [global::System.Runtime.CompilerServices.UnsafeAccessor(global::System.Runtime.CompilerServices.UnsafeAccessorKind.Method, Name = "set_Name")]
                    extern static void Set_Name(User obj, string value);
                case 1:
                    Set_Email(this, fieldValue! is null ? null : (string)fieldValue!); break;
                    [global::System.Runtime.CompilerServices.UnsafeAccessor(global::System.Runtime.CompilerServices.UnsafeAccessorKind.Method, Name = "set_Email")]
                    extern static void Set_Email(User obj, string? value);
                case 2:
                    Set_CreatedAt(this, (global::System.DateTime)fieldValue!); break;
                    [global::System.Runtime.CompilerServices.UnsafeAccessor(global::System.Runtime.CompilerServices.UnsafeAccessorKind.Method, Name = "set_CreatedAt")]
                    extern static void Set_CreatedAt(User obj, global::System.DateTime value);
                default:
                    throw new global::Avro.AvroRuntimeException($"Bad index {fieldPos} in Put()");
            }
        }
    }

}
#nullable restore
#pragma warning restore CS8618, CS8633, CS8714, CS8775

Extending generated code

Generated types are declared as partial, enabling you to extend them by providing additional partial definitions.

Example for the User type generated above.

namespace example;

public partial record User
{
    public override string ToString() => Name;
}

Access modifier

By default, all generated types are declared as public.

To change the access modifier for all generated types, include the AvroSourceGeneratorAccessModifier property in your .csproj file.

<PropertyGroup>
  <AvroSourceGeneratorAccessModifier>internal</AvroSourceGeneratorAccessModifier>
</PropertyGroup>

Supported values are public (default) and internal.

To change the access modifier of just one type, declare a partial definition for it using the desired access modifier, and annotate it with the Avro attribute.

using AvroSourceGenerator;

namespace example;

[Avro]
internal partial record User;

Records

By default, the generator uses record declarations for generated types whenever possible.

To modify this behavior for all generated types, include the AvroSourceGeneratorRecordDeclaration property in your .csproj file.

<PropertyGroup>
  <AvroSourceGeneratorRecordDeclaration>class</AvroSourceGeneratorRecordDeclaration>
</PropertyGroup>

Supported values are record (default) and class.

To change the declaration of just one type, declare a partial definition for it using the desired record or class keyword, and annotate it with the Avro attribute.

using AvroSourceGenerator;

namespace example;

[Avro]
public partial class User;

Language features

By default, the generated code utilizes the latest C# language features supported by the consuming project.

However, you can specify the C# language features to be used in the generated code to ensure compatibility with older versions of C#. For instance, setting LanguageFeatures.CSharp7_3 will restrict the generated code to features available in C# 7.3, such as excluding nullable reference types and records.

To configure language features for all generated code, include the AvroSourceGeneratorLanguageFeatures property in your .csproj file.

<PropertyGroup>
  <AvroSourceGeneratorLanguageFeatures>CSharp7_3</AvroSourceGeneratorLanguageFeatures>
</PropertyGroup>

Supported values include all flags defined in the LanguageFeatures enum.
Parsing is case-insensitive and follows the default rules for flags (using Enum.Parse).

To change used features for just one type, declare a partial definition for it, and annotate it with the Avro attribute, specifying a LanguageFeatures argument.

using AvroSourceGenerator;

namespace example;

[Avro(LanguageFeatures = LanguageFeatures.CSharp7_3)]
public partial record User;

It is also possible to enable or disable specific features.

Example for using the latest features but excluding required properties:

using AvroSourceGenerator;

namespace example;

[Avro(LanguageFeatures = LanguageFeatures.Latest & ~LanguageFeatures.RequiredProperties)]
public partial record User;

Limitations

In C#, enum types cannot be declared as partial, so it's not possible to configure code generation for just a single enum type.
A possible workaround for this is to wrap the enum schema in a record schema.

<details> <summary> Enum Wrapper Example </summary>

Before

Suit.avsc

{
  "type": "enum",
  "name": "Suit",
  "namespace": "example",
  "symbols": [
    "Hearts",
    "Diamonds",
    "Clubs",
    "Spades"
  ]
}

Suit.Avro.g.cs

// <auto-generated/>
namespace example
{
    [global::System.CodeDom.Compiler.GeneratedCode("AvroSourceGenerator", "1.0.0.0")]
    public enum Suit
    {
        Hearts,
        Diamonds,
        Clubs,
        Spades,
    }
}

After

SuitWrapper.avsc

{
  "type": "record",
  "name": "SuitWrapper",
  "namespace": "example",
  "fields": [
    {
      "name": "WrapperField",
      "type": {
        "type": "enum",
        "name": "Suit",
        "namespace": "example",
        "symbols": [
          "Hearts",
          "Diamonds",
          "Clubs",
          "Spades"
        ]
      }
    }
  ]
}

SuitWrapper.cs

using AvroSourceGenerator;

namespace example;

[Avro]
internal partial record SuitWrapper;

Suit.Avro.g.cs

// <auto-generated/>
namespace example
{
    [global::System.CodeDom.Compiler.GeneratedCode("AvroSourceGenerator", "1.0.0.0")]
    internal enum Suit
    {
        Hearts,
        Diamonds,
        Clubs,
        Spades,
    }
}

</details>

Contributing

Contributions are welcome! If you have any ideas, suggestions, or bug reports, please open an issue or submit a pull request.

License

This project is licensed under the MIT License. See the LICENSE file for details.