Extension point to wire in domain data

[dil-abertok]

Hi there,

When I am generating generic data (people, addresses, etc.), Bogus has the really lovely fluent syntax with the DataSets as properties. Now, I usually create my own methods to create bogus instances of simple domain concepts, say, my ids are all 8 digit hexadecimal, so I have a CreateId(Faker faker) method, that uses the supplied faker to generate just that without me having to express that same rule everywhere I see an Id property.
In order to wire that in, I either have a DomainFaker static class, and I do something like .RuleFor(x => x.Id, f => DomainFaker.Id(f)), or I create an instance class and extension method on Faker that returns me that instance class (passing along the faker instance), something like .RuleFor(x => x.Id, f => f.Domain().Id(). However, the extra pair of brackets after Domain sort of bugs me as idiosyncratic as none of the actual DataSets needs that.
Would it be possible to extend Faker with an "empty" Domain (partial?) class that people could use to add their extension methods to? ("Empty" as in it would probably need a property that references back the original Faker in order to have that available in the extension methods. Making it partial would probably allow for better extensibility.) That way we could do something like .RuleFor(x => x.Id, f => f.Domain.Id().

Cheers, and thanks for the awesome package!

[bchavez]

Hi. Thank you for the post.

You'll have to explain the "partial" approach more. AFAIK, the C# partial keyword won't work in this case because:

• https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/partial-classes-and-methods

All partial-type definitions meant to be parts of the same type must be defined in the same assembly and the same module (.exe or .dll file). Partial definitions cannot span multiple modules.

This means that public partial class Faker { myStuff } would only work for source code inside and defined in Bogus.dll at compile time; partial class definitions can't span multiple DLLs or EXE projects.

I agree, the two extra () in f => f.Domain().MyMethod() is a bit tacky language and ergonomic-wise, but it is the way.

I think, ideally, a C# extension property would work best here; but C# extension properties aren't a thing yet. 😭

• https://stackoverflow.com/questions/619033/does-c-sharp-have-extension-properties

So, the next best thing, alternatively, might be to add a dedicated .RuleFor extension method to Faker<T> for domain-specific data:

void Main()
{
   var faker = new Faker<MyDomainObject>()
      .RuleFor(x => x.SpecialValue, fd => fd.Domain.SpecialString());

   faker.Generate().Dump();
}

public class MyDomainObject
{
   public string SpecialValue;
}

public static class ExtensionsForDomainFakerT
{
   public static Faker<T> RuleFor<T, TProperty>(this Faker<T> fakerT, Expression<Func<T, TProperty>> property, Func<FakerWithDomain, TProperty> setter)
      where T : class
   {
      return fakerT
         .RuleFor(property, f =>
         {
            var domainFaker = new FakerWithDomain(f);
            return setter(domainFaker);
         });
   }
}

public class FakerWithDomain : Faker
{
   public FakerWithDomain(Faker existing) : base()
   {
      this.Domain = this.Notifier.Flow(new DomainDataSet());
      this.Random = existing.Random;
   }
   public DomainDataSet Domain { get; init; }
}

public class DomainDataSet : Bogus.DataSet
{
   public string SpecialString()
   {
      var value = this.Random.Replace("???###");
      return value;
   }
}

The above code seems to work on the .NET 8 SDK. It's a bit verbose to get the "Faker<T>" stuff wired up, but it seems to work.

If not, try changing .RuleFor() -> .RuleForDomain() in ExtensionsForDomainFakerT -- in this case, you'll still have to deal with some kind of uniqueness for the C# compiler to resolve the ambiguous method call. Such is life. 😞

There are probably a few ways to hack it with the DLR (dynamic language runtime and the dynamic keyword), but then you start running into possible perf issues and maybe losing IntelliSense.

Feel free to carry on the discussion after I close the thread.

Hope that helps,
Brian Chavez