Question

I have several business rules for my FormPartB object that depend on related entities Licensee and FormPartA. I’m new to FluentValidation.

What (I think) I want to do is:

• Within my FormPartBValidator, get the Licensee and FormPartA entities once, then set up a bunch of rules (i.e. Must() predicates) for FormPartB using values from those related objects.

• i.e. I dont want to fetch both external entities again within each rule defintion.

I had a couple of thoughts:

(1) Get those entities in the Validator’s constructor, above my RuleFor definitions, then save those entities as private fields,

public PartBValidator()
{
    // Get my external data and save as private fields

    RuleFor...
    RuleFor...
}

or

(2) Get those entities within the call to Validate() then save those entities as private fields:

public override ValidationResult Validate(FormPartB instance)
{
    // Get my external data and save as private fields

    return base.Validate(instance);
}

However

• In option (1) I can’t seem to access the FormPartB instance

• In option (2) Validate() doesnt seem to be working the way I thought it would (i.e. doesnt seem to get called on every validation of FormPartB.)

• And I’m not even sure that “get objects and save as private fields” is the right way to go.

Any advice?

Answer 1

I’ve handled this in applications by dependency-injecting a service into the constructor that retrieves the data that validation is dependent on, and it’s worked out quite nicely.

Here’s an example:

private readonly IFormService _service;

public PartBValidator(IFormService service)
{
    _service = service;

    var valueICareAbout = _service.GetMeFormAData();

    RuleFor...  // uses valueICareAbout
    RuleFor...
}

If you’re concerned about the performance impact of grabbing that data via the service within the rule definition, you could consider some caching options as well.