ASP.NET MVC - Where to throw the exceptions?

Question

Best practice to throw the exception if no entry found in the db?

// CONTROLLER
public ActionResult Edit(int categoryId, int id)
{
    Product target = Products.GetById(id);
    if (target == null) throw new HttpException(404, "Product not found");

    return View("Edit", target);
}

// REPOSITORY
public Product GetById(int id)
{
    return context.Products.FirstOrDefault(x => x.productId == id);
}

or

// CONTROLLER
public ActionResult Edit(int categoryId, int id)
{
    return View("Edit", Products.GetById(id));
}

// REPOSITORY
public Product GetById(int id)
{
    Product target = context.Products.FirstOrDefault(x => x.productId == id);
    if (target == null) throw new HttpException(404, "Product not found with given id");

    return target;
}

blockhead · Accepted Answer · 2010-12-23 06:37:18Z

32

Never throw an HttpException from a repository...it's the wrong level of abstraction. If you don't want your repository to return null, do something like this:

// CONTROLLER
public ActionResult Edit(int categoryId, int id)
{
    try {
       Product target = Products.GetById(id);
    }
    catch(ProductRepositoryException e) {
       throw new HttpException(404, "Product not found")
    }

    return View("Edit", target);
}

// REPOSITORY
public Product GetById(int id)
{
    Product target = context.Products.FirstOrDefault(x => x.productId == id);
    if (target == null) throw new ProductRepositoryException();

    return target;
}

Your repository should not know anything about HTTP, but your controller can know about the repository. So you throw a repository exception from the repository, and "translate" that into an HTTP Exception in the controller.

edited Dec 23, 2010 at 6:37

answered Sep 12, 2010 at 13:28

blockhead

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5 Comments

ebb Over a year ago

But then I have to create custom exceptions :(?

blockhead Over a year ago

Yes you do. And that's what you should do.

ebb Over a year ago

I'll just create a custom exception named "NotFoundException" then. Thanks for the answer :)

niico Over a year ago

How do you create this custom exception?

TylerH Over a year ago

@niico throw new Exception(), at a very basic level. If you want a different type of exception, like NotFoundException, then it is throw new NotFoundException("custom Exception message") and in your catch {} statement where you want to use it, you have catch(NotFoundException ex) instead of catch(Exception ex).

user32826 · Accepted Answer · 2010-09-12 13:27:39Z

3

Do not throw a HttpException in the Repository, as you may want to reuse that code in the future in a non-Http environment. Throw your own ItemNotFound exception if you require at least one item and handle that exception in the Controller, or return null and handle that.

answered Sep 12, 2010 at 13:27

user32826

Comments

Odys · Accepted Answer · 2014-01-11 16:45:45Z

0

I would throw HttpException in the controller, and return null from the repository.

edited Jan 11, 2014 at 16:45

Odys

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answered Sep 12, 2010 at 13:19

Nate

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1 Comment

ebb Over a year ago

Return null from the repository.. that dosent make sense - could you go a bit more in depth please?

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