FluentValidation-以嵌套结构将上下文从父级带入子级的最佳方法

Question

Problem

I have nested parent-child relationship in my classes and would want to take the parent's context into the child. A solution that I have is to create a validator for the child for every child instance. It works, but since validators are stateless by nature, they should be single-instance for an application.

Parent and Child Classes

public class Parent
{
  public string Id {get; set;}
  public List<Child> Children {get; private set;} = new List<Child>();
}

public class Child
{
  public string Name {get;set;}
}

Validators

Simple solution with multiple allocations on ChildValidator

public class ParentValidator : AbstractValidator<Parent>
{
  public ParentValidator()
  {
    // We shouldn't create a new instance of ChildValidator for each child
    RuleForEach(m=> m.Children)
      .SetValidator(m=> new ChildValidator(m.Id));
  }
}

public class ChildValidator : AbstractValidator<Child>
{
  public ChildValidator(string parentId)
  {
    RuleFor(m=> m.Name)
      .NotEmpty()
      .WithMessage($"Parent {parentId} | {PropertyName} must not be empty");
  }
}

Potential solution

One solution I have in mind is to use value tuples.

public class ParentValidator : AbstractValidator<Parent>
    {
        public static ParentValidator Instance { get; } = new ParentValidator();

        public ParentValidator()
        {
            // Must create as tuple (allocate) then convert to value tuple
            RuleForEach(m => m.Children.Select(c => new Tuple<Parent, Child>(m, c).ToValueTuple()))
                .SetValidator(ChildValidator.Instance)
                .OverridePropertyName("Child");

        }
    }

    public class ChildValidator : AbstractValidator<(Parent Parent, Child Child)>
    {
        public static ChildValidator Instance { get; } = new ChildValidator();

        public ChildValidator()
        {
            RuleFor(m => m.Child.Name)
               .NotEmpty()
               .WithMessage(m => $"Parent {m.Parent.Id} | {{PropertyName}} must not be empty");
        }
    }

Caveats

However, I find this rather troublesome due to expression trees not supporting them yet as of C# 7.3. We're now allocating Tuples instead of ChildValidator s which defeats the purpose. Also, the error message is kind of ugly because the default property name for Child becomes Item2

Test code can be accessed here

Answer 1

Any data from the "parent" entity that is required to validate the "child" entity should be included in the view model for the child entity.

Information required for the validation messages in the child entity should also be properties on the child view model:

public class AddEditChildViewModel
{
    public int ParentId { get; set; }

    public string ParentName { get; set; }
}

Then your validator doesn't have to jump through any hoops to validate data or display validation messages:

public class AddEditChildViewModelValidator : AbstractValidator<AddEditChildViewModel>
{
    public AddEditChildViewModelValidator()
    {
        RuleFor(m => m.ChildProperty)
            .Must(DoSomethingWithParentEntityData)
            .WithMessage("{0} {PropertyName} is required.", m => m.ParentName);
    }

    private bool DoSomethingWithParentEntityData(AddEditChildViewModel model, int childProperty)
    {
        // use model.ParentId for something
    }
}