I want to be able to perform validation from within my Service classes. I have a Controller action that looks something like this:
public ActionResult Edit(Post post)
{
if(!ModelState.IsValid)
return View();
_postDataService.SavePost(post);
return View("Index");
}
I don't like the fact that my _postDataService.SavePost() can save invalid data and I want to move the model validation to my _postDataService.SavePost() method. My question is what is the most elegant way to do this? And if I move my model validation to my Service method, how do I return my model errors back to my controller? Lastly, where would model validation like uniqueness of the email address go since it require's some data access? Of all the similar questions i've looked at, none of them give a straight forward way to do this.
I also considered this solution but this article is old and I have a feeling it's not up-to-date.
I assume you are doing validation by putting attributes on properties in your Post model/entity class. If so, you can validate in your service layer by doing this:
var results = new List<ValidationResult>();
var isValid = Validator.TryValidateObject(post,
new ValidationContext(post, null, null), results, true);
This is essentially what the default modelbinder does when it validates and configures the ModelState object for the controller / action.
The beauty of this approach is that you don't have to return validation errors from the service layer. You will just rely on the default modelbinder to do the above code automatically. If someone ever tries to invoke that action without checking ModelState.IsValid, just have your service method throw an exception to remind them.
Update after comment
Yes, my answer recommends doing the validation twice.
How do I feel about it? I don't mind. We use Entity Framework 4.1 with MVC, and do not use entities in MVC. Instead we use automapper to DTO the entities into a separate viewmodel layer. Our EF entities are also decorated with ValidationAttributes, which EF evaluates automatically during any DbContext.SaveChanges() operation. We apply very similar validation attributes on properties of our viewmodel classes. This might not seem DRY, and there is definitely overlap, but in some cases the validation attributes on the UI side can be different than the validation attributes in the domain model.
We do not do validation in a service layer. Our service layer is simply an application flow coordinator, and takes no responsibility for business rules. However, validation still happens twice in our application. First, by the default model binder, against the viewmodel validation rules. Then if the transaction makes it to EF, validation performed against the entities. So we are actually validating 2 separate layers.
If you think about it though, you really are tackling 2 different concerns here. In the UI, you want MVC to display validation messages to users. ModelState is great for this, since it hooks nicely with MVC validation (model binding / jquery / unobtrusive / client-validation / etc).
Conversely in the domain, you are protecting your data integrity and enforcing business rules. The domain doesn't care about displaying messages to a user. For all it knows, the client may be a machine, WCF service, or something else. The role of the domain is to prevent a transaction from occurring, and (in our case) throws an exception rather than quietly trying to "work with" the client.
Related
we are building an ASP.Net MVC application, and we ask ourselve the question where we shoud put the validation logic for incoming data.
We already have the simple validation in place: these are attributes on the viewmodel, like [required], [numeric] , [email] etc. (this is open for discussion too, btw)
But now we have some more input validation: we want to validate if the id's received from dropdownlists are genuine id's.
For example: when we receive 91 as a countryid, i have to make sure 91 is a valid countryid and not a value 'hacked into' the form by a user. Because if it is not a valid countryid, my datalayer generates an error.
Should i place this in the controllers action method, because that
method knows what is right and what is wrong when the data from the request arrives?
Should i place it in a VacancyValidator (the object is a Vacancy
object) where i put all validation logic for all vacancy related
viewmodels
Should i place it in the ViewModel because it should know how to validate itself
Should i create an attribute which validates the property which i place on the ViewModels property
Should i place it in a Vacancy[thisviewmodelsname]Validator where i put all validation logic for this specific viewmodel
Any ideas appreciated....
We already have the simple validation in place: these are attributes
on the viewmodel, like [required], [numeric] , [email] etc. (this is
open for discussion too, btw)
I would recommend FluentValidation.NET instead of Data Annotations which plays nicely with ASP.NET MVC. It provides a nice syntax for expressing complex validation logic between interdependent properties without writing millions of lines of plumbing infrastructure code (which is what you would have to do if you use Data Annotations and write a custom validator) and also allows you to unit test your validation logic very easily.
Because if it is not a valid countryid, my datalayer generates an error.
There you go - your data layer already handles this validation for you. But if you don't want to leave it to reach the data layer then you could have a validation rule for this property on the view model. If you follow my previous advice about FluentValidation.NET you will already know where to put this rule - in the corresponding validator of your view model.
You put your validation obviously to the view model. This way it is located in one spot (not scattered, hence DRY) and operational on both client and server.
For simple scenarios use Data Annotations.
For more sophisticated scenarios (enterprise scale etc) use Fluent Validation
Hope this helps.
The best way is to combine client and server validation. For client side validation you can use jquery validation plugin. It provides all standart validation patterns(like maxlength, minlength, required etc.).You can specify validation requirements in model attributes(data annotation) or directly in html. Also, it provides possibility for custom remote validation when validation result will be returned from server code.
But you should dublicate client side validation with server side. For example, use spring.net validation . I think it's the best generic and flexible framework.
I have a registration page and would like to perform some validation (in addition to the StringLength and Required annotations on my ViewModel) for duplicate usernames and email addresses. Currently I perform this validation in my controller when the registration form is posted back. I'm not sure if this is the right place to do it though.
I can't imagine the ViewModel to be the right place as it would require the ViewModel to have a reference to my UserRepository. Does it make sense to have this kind of validation in the model classes?
If so, how do I implement this on the model so I can check if the information is valid before I sent it into my repository?
Update
Code of my controller action:
if (ModelState.IsValid)
{
if (!_userRepository.Exists(registerViewModel.Username))
{
if (!_userRepository.EmailExists(registerViewModel.Email))
{
_userRepository.Add(
new User
{
Created = DateTime.Now,
Email = registerViewModel.Email,
Password = registerViewModel.Password,
Username = registerViewModel.Username
});
_userRepository.SaveChanges();
TempData["registrationDetails"] = registerViewModel;
return RedirectToAction("Confirm");
}
else
{
ModelState.AddModelError(string.Empty, "This email address is already in use.");
}
}
else
{
ModelState.AddModelError(string.Empty, "This username is already taken.");
}
}
return View(registerViewModel);
}
Update 2
Should the domain model care about such constraints as duplicate user names or email addresses or is this something that the controller layer should worry about?
Update 3
It seems that putting the validation logic in the controller makes the most sense as it can be reused in remote validation and in model validation on submit. Is something like checking for duplicates generally a thing that should be done in controllers or does it make sense to have these kind of checks in a domain model?
Thanks,
I would perform it both on the frontend (ajax perhaps) and backend - which depends on your solutions architecture.
I like to let users know immediately if there's going to be a registration issues.
In my typical setup of a data layer / business layer and presentation layer, I would perform the dup checks in the business logic and have the controller call that piece of code (in addition to an ajax lookup on the front end for users).
As a bit of a side note: I generally prefer to only use MVVM (with view models) in windows applications. Combining MVC with MVVM can make things unnecessarily complicated
I would suggest that you do this in Controllers.
The main reason is that whatever the structure of the app be, you would definitely need to use Ajax to notify the user whether the username has already been taken or not. Otherwise it's just bad usability which doesn't justify your code structure.
And for that you would like to have a action method which could ajax-ly see if the username exists or not.
Overall, it does mean you may end up with two sets of validation method (UI and model) but its all for a good cause.
Also to make a good usable site you would definitely be using a Javascript framework like knockoutjs or backbone. Thats true MVVM and in that case having your ViewModels being the Model layer classes (as Chris mentioned) is not a good idea. So basically you'll end up with two sets of validation anyways.
As Rob said in the comments, it does depend on the structure of your application. I tend to have a double validation (Validation on my ViewModels as well as validation on my service layer) to ensure that the data that hits the service is valid. This helps because my services get used by multiple clients, but the views and ViewModels are client specific. Front end validations have the advantage of instant feedback, and the backend validations help keep your data clean.
My suggestion is - For validation, such as duplicate email address and user name- to keep your validation methods in controller.
Or in your Validation Layer - which will be used in between view model and data layer
for MVC3 you will be able to add methods in controller as a actions using Remote attribute to your property in view model for instant results
You should validate in both the View (client-side) and Controller (server-side). If you have MVC 3, you can use the new RemoteAttribute. It uses jQuery to make a server-side call, in which you could check for the existence of a user or email address.
My MVC application has a well defined domain Model with each Model performing its own business rule checks.
My question is should the business rules be replicated in the view model or controller too or should I just allow the model to generate the validation errors?
Lets assume that the validation we are talking about can't be done client-side and is more complicated than simple field validation that can be done by adding validation attributes to the view model properties.
The problem with allowing the model to handle all of the validation is that the error messages it generates might not be suitable for the particular view that its coupled to, field names might not be correct for example. Also I need to add the error to the ModelState using the view model property name not the property name from the domain model.
The problem with adding the same business rule validation to the viewmodel/controller is the obvious duplication maintenance issue and it means the validation in my domain model really should never produce any errors which kind of makes it a bit pointless.
How do people usually handle this?
The solution I typically used to use in this scenario is to have the validation in the Model (or in my case typically a validation library) but add the error in the controller which allows you to catch the standard validation error like this:
public ActionResult Submit(String email)
{
string errorMessage = "";
if(Validation.IsValidEmail(email, out errorMessage))
{
ViewData.AddModelError("EmailAddress", "My Custom Error Message");
//or
ViewData.AddModelError("EmailAddress", errorMessage);
}
}
This may not be exactly what you are looking for but it might help you come up with a way of maximising re-usable code whilst still being able to customise it.
I used to do it like this - but I bit the bullet and my most recent applications use standard error messages everywhere - my motivation for this is that users are increasingly comfortable with short-simple validation message and field names are not required in the message if the message is displayed inline with the form field rather than as a summary. This also allows me to put all my rules/messages in data annotations and I find that it works a treat.
Say I have an object that gets some data from HttpPost and some from the database. I think I want to allow the ModelBinder to go to the database/repository for the that data missing from the post. In practice, is this a good or bad idea?
I've decided to edit my original answer given my thinking on these types of things has evolved since early 2010.
In my original answer, I basically expressed that, while my instincts told me you shouldn't do this, I was uncomfortable saying we shouldn't without being able to articulate why.
Now, I'd recommend against this on the grounds that the responsibility of a Model Binder is to translate a user request into a Request Model and that retrieving data outside of what can be derived from the request goes beyond this scope of responsibility.
I would say a bad idea. The idea of the model binder is that it takes the parameters from the request and creates your model from those. If your model binder, behind the scenes, fills in some of the details from the database this breaks the paradigm. I'd much rather expose the database call in my controller by explicitly fetching the required extra data from the database directly. Note that this could be refactored into a method if used frequently.
I think this is perfectly fine and use this technique all the time.
The only arguments against are very pedantic and amount to arguing over philosophy. IMHO you can put "fill in missing posted data" code into you MVC app as a method in your base controller vs. method in you ActionFilter vs method in you ModelBinder. It all depends on who get what responsibility. To me the model binder can do a lot more than simply wire up some properties from posted values.
The reason I love doing database calls in my modelbinder is because it helps clean up your action methods.
//logic not in modelbinder
public ActionResult Edit( KittyCat cat )
{
DoSomeOrthagonalDatabaseCall( cat );
return View( new MODEL() );
}
vs.
//logic in model binder
public ActionResult Add( KittyCat cat )
{
return View( new MODEL() );
}
It violates the way MVC is supposed to work. ModelBinder is for binging Models from the data that comes from the view. Populating missing info from the database is something that is supposed to be handled by the controller. Ideally, it would have same data layer/repository class that it uses to do this.
The reason it should be in the controller is because this code is business logic. The business rules dictate that some data may be missing and thus it must be handled by the brains of the operation, the controller.
Take it a step further, say you want to log in the DB what info the user isn't posting, or catch an exception when getting the missing data and email admins about it. You have to put these in your model binder this way and it gets more and more ugly with the ModelBinder becoming more and more warped from its original purpose.
Basically you want everything but the controller to be as dumb and as specialized as possible, only knowing out how to carry out its specific area of expertise which is purely to assist the controller.
I would say, no.
Here's why: It would create a dependency on your database for testing your controller actions that would not be easy to abstract out.
I would say it is ok. The argument that creates dependency to database is a false argument for 2 reasons:
1- Database access should be abstracted via repository interfaces. Repository interfaces are part of the domain model and their implementation is part of the infrastructure/data access layer. So there is no dependency to the database.
2- Model Binders and Controllers are both part of presentation layer implemented using ASP.NET MVC Framework. If Controllers are allowed to access database using repository interfaces, how come Model Binders are not allowed?
Also, there are situations that you'd "better" fill the missing data in your model from Model Binders. Consider the scenario where you have a drop-down list on your view. The first time the view is loaded, the drop-down list is populated. The user submits the form but the validation fails. So you'll need to return the form again. At this stage, you'll have to re-populate the list in the Model for the drop-down list. Doing this in Controller looks ugly:
public ActionResult Save(DocumentViewModel viewModel)
{
if (!ModelState.IsValid)
{
viewModel.Categories = _repository.GetAll();
return View(viewModel);
}
}
I believe the initialization of Categories here is ugly and like a code smell. What if you had a few properties that needed to be filled out from database? What if you had more than 1 action that had DocumentViewModel as an argument? You'd have to repeat this ugly step over and over. A better approach is to fill all the properties of the model using the Model Binder and pass it to the Controller. So the object that is passed to the controller is in a "consistent" state.
This might be too opinionated a question, but looking for help!
I have been trying to refine my ASP.NET MVC program structure. I just started using it at preview 5 and it is my first foray into business application development -- so everyting is new!
At the controller level, I have a service object responsible for talking to the repository and taking care of all business logic. At the action level, I have an object that holds all view data -- user input and generated output -- that I'll call view object (is there a general term for this?). Unlike most examples I see, this object is not a database object, but an object specific to the view.
So now I want to add user validation. The problem is, I'm not sure where to put it. It makes the most sense to me to do it in the Service layer. The Service layer is responsible for all the business logic and validation is business logic. On the other hand, most validation frameworks that I see are for validating an object, which makes me think the view object should be validation aware. Finally, there are some validation methods that would require a database connection (checking if a user input field has a corresponding database record for example), and the view object has no concept of a database, only the Service.
So some options I see are:
Do validation in the Service.Method on the parameters passed to the method.
Do validation in the view object before calling Service.Method.
Do validation in the view object but make the Service.Method require a view object reference so it is initiating the validation on the object.
I'm sure there are more. I'm curious of how other people handle user input validation in the MVC sense. I've previously used the Enterprise Validation Block and liked being able to use stock validators for everything, but I'm not sure how to make it fit into a seperate view object and service layer. It would be easy if they (view object / service) were the same object, which is maybe what people do? Like I said, its all new to me and I'm looking for best practice / patterns.
I typically do basic validation (required fields, email format, etc.) in the controller action when the form is submitted. I then let the business layer handle validation that requires business knowledge. I usually double check the basic stuff in the business layer as well, so if I expose that logic through web services or use it in another application later, I still have validation where it is most important (IMO).
There are some interesting links on this
MVC & MS Validation Application Block
MVC & Data Annotation Validators
Form Validation video
Personally, i've added validation to my Service layer objects (first two links). This way, if any method in any controller decides to call my service method .. the logic is all checked and boxed in one location. DRY.
That said, i also have some UI validation (3rd link) .. to reduce the roundtrip time.
Lastly, the current MVC dll's have the ability to pass error messages back to the UI .. so the view can display them nicely. Check out :-
ViewData.ModelState.AddModelError(key, message)
hth!
Check the following blog posts
http://blog.codeville.net/2008/09/08/thoughts-on-validation-in-aspnet-mvc-applications/
http://www.emadibrahim.com/2008/09/08/client-server-side-validation-in-aspnet-mvc/
Take a look at the S#arp Architecture project. Validation is handled on the model to ensure that no entity is persisted to the database in an invalid state. It does this by using NHibernate.Validator and attaching it to NHibernate's save and update events.
Personally, this approach makes the most sense to me since you don't have to duplicate your validation logic in multiple controllers.
I was afraid I'd get no replies for my post, happy to be wrong!
I've read those links before, but probably a month or more ago, and re-reading them with what I understand now has been very helpful. I really like Steve Sanderson's post with the sliding scale, but wish he would show an example of validating something at the right-end of the spectrum.
As an example in his blog he gives: " 'usernames must be unique' will probably be enforced in your database". So would this be something like:
public static void SavePerson(Person person)
{
// make sure it meets some format requirement
// in this case the object is responsible for validation and the service layer is the caller
person.EnsureValid();
// todo: action to verify username is unique by checking database
// in this case the service layer is responsible for calling and implementing validation
// todo: action to save to database
}
This makes sense, and would show my trouble grasping where to put validation as it is inside both the service layer (very unique name) and view-object (verify formats).
Another concern I have is the service layer starts to balloon with validation logic. Maybe split it out to a different class or something? In my case some validation logic might be shared between services, so I would like to think of a DRY way to implement this. Fun stuff to think about!
Emad Ibrahim's link is great in that once I start to understand this process a bit more I was going to look for a way to generate javascript client-side validation using the same set of rules without having to repeat code. He already has that :)
I have heard about S#arp but not sat down and seen how it works (I'm not sure if there is much in the way of demos on it, or if downloading the code is the demo!). I'm not sure if doing validation on the database model only would be sufficient. It seems to me there would be plenty of valid model states with regards to the database that business logic would say are invalid (such as date ranges / must be before / after / etc). Those are the cases that are wracking my brain :)
Also, a link I liked (googled it after I saw Emad reply to Steves post with BLL and no idea what it meant... duh):
http://en.wikipedia.org/wiki/Business_logic_layer
So I didn't know it, but I think this is the model I'm writing to: Business Process object that handles data interactions, and Business Entities that are logical models rather than database models. I think I need to start reading some more fundamental patterns and practices with this stuff to better understand the concepts (it seems like a lot of this is stuff Java people write vs. .NET people). It might be time to take a step back :)
I have come across this same issue in a recent project. First, to restate the problem, I am trying to follow the domain-centric approach of DDD. I have entities composed into aggregates that can validate themselves, and the repositories verify validity on save. The UI can also get validity information from an aggregate in order to display error feedback to the client. The general approach is to leverage as much as possible ASP.NET MVC's model binding, and validation/form UI helpers. This creates the simple UI flow: 1) bind, 2) validate, 3) if valid, save, else re-populate view.
However, it is not directly obvious how to do leverage ASP.NET MVC and this simple flow when DDD services are involved. Originally, I developed my services as such:
public class SomeProcessService
{
public Result Execute(int anAggregateID, int anotherAggregateID, string someData)
{
// validate input
// if invalid, return failures
// else
// modify aggregates
// using (transaction)
// {
// save aggregates
// commit
// }
// return success
}
}
The problem is that the validation and the save are inextricably linked in the method. To leverage the MVC model binding, we need something that serves as a model to bind to. I am refactoring to this:
public class SomeProcessService
{
public class Request : IValidateable
{
public int AggregateID {get;set;}
public int AnotherAggregateID {get;set;}
public string SomeData {get;set;}
public Result Validate()
{
// validation
}
}
public void Execute(Request request)
{
// validate input by calling request.Validate()
// if invalid, throw new ValidationException(request)
// else
// modify aggregates
// using (transaction)
// {
// save aggregates
// commit
// }
// return success
}
}
This repurposes the Parameter Object pattern to separate method input validation. I can bind to a SomeProcessService.Request object in my controller, as well as get validation information there. If all is well, from my controller I initiate the service call using the Request object as the parameter. This approach seems to happily marry DDD services with ASP.NET MVC validation requirements.