不错的简单ASP.NET MVC2 C＃问题（切换语句）

Question

Good Morning,

I have the following line of code:

 var viewModel = new ClassifiedsBrowseViewModel
        {
            Category = categoryModel,
            Listings = categoryModel.Listings.OrderBy(c => c.Price).ToList()
        };

All is good in the world, and this code works fine. But now I would like to add a switch statement that allows me to change what I am ordering listings by (in the above code it is ordered by price).

So I obviously cannot but the switch statement within the new model deceleration, so I will be putting the switch statement above eg:

  switch(searchCriteria)
            {
                case "Price":
                    break;
                case default:
                    break;
            }

So my question is how do I link the two? BTW listing is declared within the ViewModel as:

 public List<Listing> Listings { get; set; }

I thought I could declare a Listings variable in the Controller and then set that variable in the Switch to categoryModel.Listings.OrderBy(c => c. [Search Criteria] ).ToList() and then simply have Listings = Listings ?

Many Thanks, J

Using

Using Ribon's Method:

 var viewModel = new ClassifiedsBrowseViewModel
        {
            Category = categoryModel,
            Listings = categoryModel.Listings.OrderBy(c =>
            {
                switch (searchCriteria)
                {
                    case "Price": return c.Price;
                    case "FuelType": return c.FuelType;
                    default: return c.Price;
                }
            }).ToList()
        };

Answer 1

I know nothing about Linq statements, bu can't you just do the folowing ?

var viewModel = new ClassifiedsBrowseViewModel
        {
            Category = categoryModel,
            Listings = categoryModel.Listings.OrderBy(c => {
                switch (searchCriteria) {
                    case "Price" : return c.Price; break;
                    default: return c; break;
                }
            }).ToList()
        };

Answer 2

You could use your linq statement in your switch statement such as

switch(searchCriteria)
            {
                case "Price":
                    viewModel.Listings = categoryModel.Listings.OrderBy(c => c.Price).ToList()
                    break;
                case default:
                    viewModel.Listings = categoryModel.Listings.OrderBy(c => c.SomeOtherField).ToList()
                    break;
            }

Answer 3

I would have:

IEnumerable<Foo> listings = categoryModel.Listings;
switch(sortOrder) {
    case "x":
       listings = listings.OrderBy(l => l.Something);
       break;
    case "y":
       listings = listings.OrderBy(l => l.Whatever);
       break;
}

And then use the listings variable in the model creation:

...
Listings = listings
...

( or listings.ToList() )

Answer 4

IMO a nice, clean and readable solution would be to create an extension method that accepts an IQueryable, and an enumeration which would represent the various ordering options.

public static IOrderedQueryable<Listing> WithListingOrder(this IQueryable<Listing> source, PriceOrderingOptions orderBy)
{
   switch (orderBy)
   {
      case ListingOrderingOptions.Price:
         return source.OrderBy(x => x.Price);
      ... // other enumerations
   }
}

I have a generic ordering extension method (taking a T,TKey), but in your case since your working with a string (search criteria), can't use generics here.

But i think expressing the ordering options as an enumeration should prevent "magic strings".

And use it like this:

var searchCritera = ListingOrderingOptions.Price;

var viewModel = new ClassifiedsBrowseViewModel
        {
            Category = categoryModel,
            Listings = categoryModel.Listings.WithListingOrder(searchCriteria)
            }).ToList()
        };

The main benefit here is your hiding the ugly switch behind the extension - the goal here is to keep your controller clean.