To sort a list of objects by TWO properties

Question

On this topic: How to sort list with complex object by one of its properties? is explained as ordering by a property, but as ordering by two?

Taking into account the following product class:

+-------------------+--------------------+ 
| Produto                                | 
+-------------------+--------------------+ 
| Código            | int                | 
| Nome              | string             | 
| Preço             | double             | 
| Categoria         | Categoria          | 
+-------------------+--------------------+ 

And the class category

+-------------------+--------------------+ 
| Categoria                              | 
+-------------------+--------------------+ 
| Código            | int                | 
| Nome              | string             | 
+-------------------+--------------------+ 

And imagining a list of products.

How can I sort the list by alphabetical order of your category name, followed by alphabetical order of your name? You can use the IComparer?

Answer 1

Do with Linq, first make sure to be referencing:

using System.Linq;

Then use it like this:

var ordenada = lista.OrderBy(m => m.Categoria.Nome).ThenBy(m => m.Nome);

Use the return list ordenada to go through. Like this:

foreach (var item in ordenada)
{
    Console.WriteLine(item.Nome + " - " + item.Categoria.Nome);
}

Using query syntax this way is equivalent to the previous:

var ordenada = from m in lista
               orderby m.Categoria.Nome, m.Nome
               select m;

The OrderBy returns a list of type IOrderedEnumerable<T> so it is only possible to use the ThenBy after the OrderBy. If it were necessary to add a third property it would come with another ThenBy and so on.

If you just wanted to change the original list without having a new ordered copy, you could do so by calling the method ToList() in that way:

lista = lista.OrderBy(m => m.Categoria.Nome).ThenBy(m => m.Nome).ToList();

See that it would also be possible to call the OrderBy twice that way:

var ordenada = lista.OrderBy(m => m.Nome).OrderBy(m => m.Categoria.Nome);

It would be necessary to invert the sequence, since the entire list would be ordered twice (which should be less performatic). But besides not being very semantic, it is also not the form of use for which the OrderBy was designed.