MVC FluentValidation with entity framework in separate .dll

Question

I have a separate .dll with our database model and partial classes etc in using FluentValidation which works fine (it's to be used by both by desktop barcoding terminals and also by our website).

For the desktop apps I can read and display all errors like below

public override int SaveChanges()
    {
        var errors = this.GetValidationErrors();
        if (errors.Any())
        {
            //handle validation errors
            return 0;
        }
        else
        {
            return base.SaveChanges();
        }
    }

For the MVC site I can set up validators on individual models or create data annotations and get those working okay (which is not what I want). The thing I can't get my head around is how I can force my models to map to my entities in a way that I can display the fluent validation messages in the views. I don't want to have two separate sets of logic to be maintained and the barcoding apps and website must use the same.

Do I have to map my entities directly to the views? which i've been led to believe is a bad thing and not very flexible. Or is there a way of stating that a field in a model maps back to an attribute of one of my entities? perhaps an annotation of some description.

EDIT:

Just some clarification for the types of validation i'll need.

most front end input type validation will still stay in the viewModels (required/length/password matches etc - basically all the stuff I can use for client side validation as well). But there are all the business logic validations that I don't want there. Things like email addresses must be validated before other options can be set, account numbers must be of a particular format based on name (stuff I can't do with a regex). This particular date is not a valid delivery date etc.

I guess one thing I could do is add these to the ValidationSummary somehow and display them separate from the individual fields.

score 1 · Answer 1 · answered Apr 04 '13 at 19:14

I think you're just looking at the situation wrong. What MVC is all about is a separation of concerns. There's things the database needs to know about that your views could care less, and vice versa. That's why the recommended practice is to use view model with your views and not the entity itself.

Validation is much the same. Something like the fact that a password confirmation needs to match the password the user entered does not concern the database at all. Or more appropriately, something like a validation on minimum amount of characters in the password does not concern the database, either; it will only ever receive a salted and hashed version of the password. Therefore it would be wrong to put this kind of validation on your entity. It belongs on the view model.

When I first started out using MVC, I used to add all the validation logic to my entity class and then go and repeat that same validation on my view model. Over time, I started to realize that very little of the validation actually needs to be on both. In fact, the largest majority of validation will should just go on your view model. It acts as a gatekeeper of sorts; if the data is good enough to get through your view model, it's good enough for your database. The types of validation that make sense on your entity is things like Required, but even that is really only necessary on a nullable field that must have a value by the time it gets to your database. Things like DateTimes are non-nullable by default, and EF is smart enough to make them non-nullable on the tables it creates by default. MaxLength is at times worthwhile if there should be a hard limit on the length of a text field in your database, but more often than not, nvarchars work just fine.

Anyways the point is that if you actually sit down and start evaluating the validation on your entity, you'll likely see that most of it is business logic that only applies to how your application works and not to how the data is represented at the database level. That's the key takeaway: on your entity, you only need the validation that's necessary for the database. And that's generally pretty thin.

Hi Chris and thanks, I updated my question to explain the types i'll need better. Unfortunately we do have a ton of criteria that needs to be met before even the simplest of updates can take place, and as two separate programs have to use it I need it in one place really. — Peter Lea, Apr 04 '13 at 19:58
Your view models can be shared, just as well. Just add them to your class library. The only point I was making is that really you should be looking at your view model in terms of validation. The only things you need to worry about from the entity perspective is nitty-gritty database integrity issues. — Chris Pratt, Apr 04 '13 at 20:58

score 1 · Accepted Answer · answered Apr 08 '13 at 17:00

Just an update. to get the two tier validation that i needed i had to mark all my entity model classes as IValidatable. Then i overrode the validate method for each class and invoked my fluent validation validator method there, passing back the errors needed. for the modelstate.addmodelerror i set the key as the field name and it mapped back okay. bit more code but it works. if i find a better way to do this ill update.

MVC FluentValidation with entity framework in separate .dll

2 Answers2