Fluent validator to check if entity with ID exists in database - servicestack

Question

I'm trying to write a custom validator that will check if an entity exists in the database, using OrmLite. The problem is that the type arguments for IRuleBuilder can no longer be inferred from usage.
I have to write the method call like this:
RuleFor(r => r.Id).Exists<DtoName, int, EntityName>()
But I want to write it like this:
Rulefor(r => r.Id).Exists<EntityName>()
This happens because IRuleBuilder has two type parameters and the method is an extension method. Is there a smart, fluent way to design this and make the function call preferably like the second version?
Here is code for my extension method and my validator:
public static class AbstractValidatorExtensions
{
public static IRuleBuilderOptions<T, TProperty> Exists<T, TProperty, U>(this IRuleBuilder<T, TProperty> ruleBuilder)
{
return ruleBuilder.SetValidator(new EntityExistsValidator<U>());
}
}
public class EntityExistsValidator<T> : PropertyValidator
{
public EntityExistsValidator() : base("Entity does not exist") {}
protected override bool IsValid(PropertyValidatorContext context)
{
return HostContext.Resolve<Repository>()
.Exists<T>((int)context.PropertyValue);
}
}

Answer 1

My experience with FluentValidation is that you’re trying to push more and more logic into validators. I would not do this as it adds too much complexity. My rule of thumb is to validate discrete property values only. Example: I would just use FluentValidation to check if property int Id is 0 or greater than 0. The check if the entity already exists I would move to another service (often called “the business logic”).

Answer 2

You'll need to a Custom Validator for custom validation to access dependencies, something like:
RuleFor(x => x.Id)
.Must(id =>
{
using (var db = HostContext.AppHost.GetDbConnection(base.Request))
{
return !db.Exists<EntityName>(x => x.Id == id);
}
})
.WithErrorCode("AlreadyExists")
.WithMessage("...");
I'd also consider just doing validation that use dependencies in your Services instead:
if (Db.Exists<EntityName>(x => x.Id == request.Id))
throw new ArgumentException("Already Exists", nameof(request.Id));