SurrogateAttribute.Fody 0.5.26

A Fody weaver that allows mapping attributes to any other attributes, thus making C#'s attributes a bit more useful.

Installation

Install Fody and SurrogateAttribute.Fody:

PM> Install-Package Fody
PM> Install-Package SurrogateAttribute.Fody

Then add FodyWeavers.xml file to your .csproj with the following content:

<Weavers>
  <SurrogateAttribute />
</Weavers>

This includes SurrogateAttribute Fody add-in to the IL weaving process.

See Samples for a working solution.

In a nutshell

Instead of having:

class Cat
{
    [Required(ErrorMessageResourceType = typeof(Translations), ErrorMessageResourceName = nameof(Translations.NameRequired))]
    [MinLength(3, ErrorMessageResourceType = typeof(Translations), ErrorMessageResourceName = nameof(Translations.NameBadLength))]
    [MaxLength(10, ErrorMessageResourceType = typeof(Translations), ErrorMessageResourceName = nameof(Translations.NameBadLength))]
    [DisplayAttribute(ResourceType = typeof(Translations), Name = nameof(Translations.CatName))]
    public string Name { get; set; }
}

you can create attributes that implement ISurrogateAttribute and have reusable abstractions suitable to your requirements, e.g.

[AttributeUsage(AttributeTargets.Property)]
class RequiredWithLengthAttribute : Attribute, ISurrogateAttribute
{
    [PropertyDefaultValue(1)]
    public int MinLength { get; set; }

    [PropertyDefaultValue(10)]
    public int MaxLength { get; set; }

    [PropertyDefaultValue(typeof(Translations))]
    Type TranslationResourceType { get; }

    Attribute[] ISurrogateAttribute.TargetAttributes => [
        new RequiredAttribute { ErrorMessageResourceType = TranslationResourceType, ErrorMessageResourceName = nameof(Translations.NameRequired) },
        new MinLengthAttribute(MinLength) { ErrorMessageResourceType = TranslationResourceType, ErrorMessageResourceName = nameof(Translations.NameBadLength) },
        new MaxLengthAttribute(MaxLength) { ErrorMessageResourceType = TranslationResourceType, ErrorMessageResourceName = nameof(Translations.NameBadLength) },
    ];
}

[AttributeUsage(AttributeTargets.Property)]
class TranslationAttribute(string translationKey) : Attribute, ISurrogateAttribute
{
    Attribute[] ISurrogateAttribute.TargetAttributes => [
        new DisplayAttribute { ResourceType = typeof(Translations), Name = translationKey }
    ];
}

so Cat can be simplified:

class Cat
{
    [RequiredWithLength(MinLength = 3)]
    [Translation(nameof(Translations.CatName))]
    public string Name { get; set; }
}

Attributes implementing ISurrogateAttribute are replaced with their TargetAttributes at build time using IL weaving.

Supported features

TODO