Kirill.Lutzow Kirill.Lutzow - 4 months ago 20
C# Question

C# - sort List<SomeClass> by using custom CompareTo method

I have the following classes hierarchy:

abstract class Product : IComparable
{
public string Name { get; set; }
public decimal Price { get; set; }
public string Barcode { get; set; }

public int CompareTo(object obj)
{
int ret = -1;
if (String.Compare(this.GetType().Name, obj.GetType().Name,StringComparison.Ordinal) == 0)
ret = 0;

return ret;
}
}

abstract class Book : Product
{
public int PagesCount { get; set; }
}

class ProgrammingBook : Book
{
public string ProgrammingLanguage { get; set; }
}

class CulinaryBook : Book
{
public string MainIngridient { get; set; }
}

class EsotericBook : Book
{
public int MininumAge { get; set; }
}
abstract class Disc : Product
{
internal enum Content
{
Music,
Video,
Software
}

public Content DiscContent { get; set; }
}

class CdDisc : Disc
{

}

class DvdDisc : Disc
{

}


And I trying to sort following collection by using IComparable interface method CompareTo:

List<Product> products = new List<Product>
{
new DvdDisc {Name = "The lord of the rings 2",DiscContent = Disc.Content.Video,Price = 200M,Barcode = "5435443-2"},
new CdDisc {Name = "Antonio Vivaldi: best picks",Price = 700M, DiscContent = Disc.Content.Music,Barcode = "4543765-565"},
new CulinaryBook{Name = "Midterranian foods",MainIngridient = "Salmon",PagesCount = 436,Price = 350M,Barcode = "41457561-897"},
new CdDisc{Name = "Windows XP", DiscContent = Disc.Content.Software, Price = 950M, Barcode = "5433668-4"},
new EsotericBook{Name = "Russian Freemasonry 1731-2000",MininumAge = 21,PagesCount = 2100,Price = 3000M,Barcode = "6464632-876"},
new CdDisc {Name = "The best of Mussorgsky",Price = 300M, DiscContent = Disc.Content.Music,Barcode = "5435436-567"},
new ProgrammingBook{Name = "CLR via C#",PagesCount = 900, Price = 1110M,ProgrammingLanguage = "C#",Barcode = "5546533-2446"},
new DvdDisc {Name = "The lord of the rings 1",DiscContent = Disc.Content.Video,Price = 200M,Barcode = "54354423-2"},
new ProgrammingBook{Name = "ASP.NET MVC 4",PagesCount = 800,Price = 1200M,ProgrammingLanguage = "C#",Barcode = "46476573-65"},
new EsotericBook{Name = "Russian Freemasonry in it's future and past",MininumAge =19, PagesCount = 900, Price = 2342M,Barcode = "3656353-24"},
new CulinaryBook{Name = "Traditional Polish dishes",MainIngridient = "Red meat",PagesCount = 630,Price = 840,Barcode = "54634234-5"}
}; products.Sort();


Output list should look like this:

1.1 Programming books

1.2 Culinary books

1.3 Esoteric books


2.1 Cd discs sorted by content

2.2 DVD discs sorted by content


My current CompareTo method does only part of the job - comparing classes by name.

Answer

This is a working example that will render the exact same output:

1.1 Programming books 
1.2 Culinary books 
1.3 Esoteric books 

2.1 Cd discs sorted by content 
2.2 DVD discs sorted by content 

enter image description here

I also added IComparable<Product> to more easily make it comparable with other products.

 abstract class Product : IComparable<Product>
    {
        public string Name { get; set; }
        public decimal Price { get; set; }
        public string Barcode { get; set; }
        protected abstract int InternalSortOrder { get; }
        protected virtual string SortBy { get {return Name;} }


        public int CompareTo(Product obj)
        {
            var sameType = string.Compare(GetType().Name, obj.GetType().Name, StringComparison.Ordinal) == 0;

            var sameBaseType = GetType().BaseType != null && obj.GetType().BaseType != null &&
                               string.Compare(GetType().BaseType.ToString(), obj.GetType().BaseType.ToString(),
                                   StringComparison.Ordinal) == 0;


            // They have the same base type, but not the same type. Order by base type first.
            if (!sameType && !sameBaseType && GetType().BaseType != null && obj.GetType().BaseType != null)
            {
                // Order by base type first.
                return string.Compare(GetType().BaseType.ToString(), obj.GetType().BaseType.ToString(),
                    StringComparison.Ordinal);
            }

            // it's the same base type (eg. book or disc)
            if (sameBaseType)
            {
                // Order by sort order.
                if (obj.InternalSortOrder != this.InternalSortOrder)
                {
                    return InternalSortOrder.CompareTo(obj.InternalSortOrder);
                }
            }

            if (sameType)
            {
                // Same sort order. We sort by name.
                return string.Compare(SortBy, obj.SortBy, StringComparison.Ordinal);
            }

            // Order by Type.
            return string.Compare(GetType().Name, obj.GetType().Name, StringComparison.Ordinal);
        }

    }

    abstract class Book : Product
    {
        public int PagesCount { get; set; }
    }

    class ProgrammingBook : Book
    {
        public string ProgrammingLanguage { get; set; }

        protected override int InternalSortOrder
        {
            get { return 1; }
        }
    }

    class CulinaryBook : Book
    {
        public string MainIngridient { get; set; }

        protected override int InternalSortOrder
        {
            get { return 2; }
        }
    }

    class EsotericBook : Book
    {
        public int MininumAge { get; set; }

        protected override int InternalSortOrder
        {
            get { return 3; }
        }
    }
    abstract class Disc : Product
    {
        internal enum Content
        {
            Music,
            Video,
            Software
        }

        protected override string SortBy
        {
            get { return DiscContent.ToString(); }
        }

        public Content DiscContent { get; set; }
    }

    class CdDisc : Disc
    {
        protected override int InternalSortOrder
        {
            get { return 1; }
        }
    }

    class DvdDisc : Disc
    {
        protected override int InternalSortOrder
        {
            get { return 2; }
        }
    }

UPDATE:

I've added virtual SortByin Product. It will go to Name by default, but Disc will return Content.

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