JSON serializer & custom validation

JSON serializer support

The generator detects which serializers are available and produces the corresponding converters:

Serializer	Generated converter	Registration
System.Text.Json	PatchFieldJsonConverterFactory	options.Converters.Add(new PatchFieldJsonConverterFactory())
Newtonsoft.Json	PatchFieldNewtonsoftConverter	settings.Converters.Add(new PatchFieldNewtonsoftConverter())

Both are generated if both packages are referenced. No converter is auto-registered — you choose which one to use, or write your own.

Custom validation

Simple validator

Implement IDtoValidator<T> and point to it from the attribute:

public class MyCreateValidator : IDtoValidator<CreatePlayerRequest>
{
    public DtoValidationResult Validate(CreatePlayerRequest instance)
    {
        var result = new DtoValidationResult();
        if (instance.Name.HasValue && instance.Name.Value.Length < 3)
            result.AddError("name", "must be at least 3 characters.");
        return result;
    }
}

[CreateDto(Validator = typeof(MyCreateValidator))]
public class Player { ... }

When a validator is set, Validate() delegates entirely to it — the default generated rules are replaced.

FluentValidation

When FluentValidation is installed, the generator additionally produces:

• FluentDtoValidator<T> — base class bridging FluentValidation with IDtoValidator<T>
• {RequestName}CreateBaseValidator — contains the generated required/null rules
• {RequestName}UpdateBaseValidator — contains the generated null rules

Inherit to extend:

public class MyCreateValidator : CreatePlayerRequestCreateBaseValidator
{
    public MyCreateValidator()
    {
        RuleFor(x => x.Name)
            .Must(f => !f.HasValue || f.Value.Length >= 3)
            .WithMessage("Name must be at least 3 characters.");
    }
}

[CreateDto(Validator = typeof(MyCreateValidator))]
public class Player { ... }

Or start from scratch:

public class MyCreateValidator : FluentDtoValidator<CreatePlayerRequest>
{
    public MyCreateValidator()
    {
        // your rules only
    }
}

Related guides

• Full CRUD with SQLite — end-to-end project with [CrudApi], relationships, Query DSL, observability, and PatchField tri-state demo
• Modeling Relationships & Query DSL — [OneToOne] / [OneToMany], dot-notation filtering, every DSL operator with SQL translations
• PatchField Tri-State — the null-vs-missing problem and PatchField<T> with pattern-matching handlers
• Declarative Observability — [Log] + [Trace] for structured logging and OpenTelemetry spans on CRUD stores

Requirements

• .NET 6+ (or .NET Framework with SDK-style projects and System.Text.Json NuGet)
• required keyword needs C# 11 / .NET 7+ (optional — without it all properties are optional in Create)

License

MIT