List.Sort by property name - Including subclasses

Question

I have a bit of a challenge. I need to sort a List of objects, and I need to sort it from a string representing the path to the property in any sub class. I need to use the List.Sort() and not OrderBy().

Lest make a simple example. I have a list of persons represented by two sub classes for identification and name

public class NameParts
{
    public String FirstName { get; set; }
    public String LastName { get; set; }
}

public class Identification
{
    public String NiNumber { get; set; }
    public NameParts Name { get; set; }
}

public class Person
{
    public String Email { get; set; }
    public String Phone { get; set; }
    public Int16 Age { get; set; }

    public Identification Id { get; set; }
}

Now I need to sort the list by age. Very simple

 public static void SortByAge(List<Person> listToSort)
 {
     listToSort.Sort((x, y) => x.Age.CompareTo(y.Age));
 }

And even by NiNumber and FirstName it is fairly simple this way

 public static void SortByNiNumber(List<Person> listToSort)
 {
      listToSort.Sort((x, y) => x.Id.NiNumber.CompareTo(y.Id.NiNumber));
 }

 public static void SortByFirstName(List<Person> listToSort)
 {
      listToSort.Sort((x, y) => x.Id.Name.FirstName.CompareTo(y.Id.Name.FirstName));
 }

Now comes the tricky part. I need to perform all the above sorts giving a string that represents the path to theproperty to sort by. Like "Id.Name.FirstName"

So I need

 public static void SortByAny(List<Person> listToSort, String sortBy)
 {
   //??????
 }

That can be called with

 List<Person> theList = new List<Person>();
 SortByAny(theList, "Age");
 SortByAny(theList, "Id.NiNumber");
 SortByAny(theList, "Id.Name.FirstName");

I know I need to use reflection for this, and I have managed to do so but I cannot get further than properties in the Person Class itself, so I probably need to do something else, and this is where I'm stuck.

Does anyone have some brilliant ideas on how to solve this?

Thanks

You could probably use part of this solution: http://stackoverflow.com/questions/4473928/c-sharp-dynamic-string-property-path — E. Mourits, Jul 01 '16 at 06:37
Can you explain why you need this? Maybe there is another solution to your problem — Maxim Kosov, Jul 01 '16 at 07:27
I need it because I would prefer a single sort method over implementing sort method i each of 10-100 classes with Switches for all sort options. of course that would work well, but gives me a lot of code to maintain — Beaker, Jul 01 '16 at 07:41
I'm trying to see if I can get something out of that. But I'm not quite a master in reflection though :) — Beaker, Jul 01 '16 at 07:51

score 0 · Answer 1 · 2016-07-01T08:35:16.100

Because getting properties by reflection is quite hard to do, just use and modify this code:

public static void SortByAny(List<Person> listToSort, String sortBy)
{
    if (sortBy == "Email")
        listToSort.Sort((x, y) => x.Email.CompareTo(y.Email));
    else if (sortBy == "Phone")
        listToSort.Sort((x, y) => x.Phone.CompareTo(y.Phone));
    else if (sortBy == "Age")
        listToSort.Sort((x, y) => x.Age.CompareTo(y.Age));
    else if (sortBy == "Id.NiNumber")
        listToSort.Sort((x, y) => x.Id.NiNumber.CompareTo(y.Id.NiNumber));
    else if (sortBy == "Id.Name.FirstName")
        listToSort.Sort((x, y) => x.Id.Name.FirstName.CompareTo(y.Id.Name.FirstName));
    else if (sortBy == "Id.Name.LastName")
        listToSort.Sort((x, y) => x.Id.Name.LastName.CompareTo(y.Id.Name.LastName));
}

Thanks for the suggestion This was more or less what I came up with, but the problem is with drilling down deeper.. — Beaker, Jul 01 '16 at 07:37

score 0 · Answer 2 · answered Jul 01 '16 at 07:22

0

Do you really need to put reflection in place? If u need to sort the list by a specific and determined number of "paths" i would suggest you implementing it in a fixed way, going straight ahead with sorting. maybe a switch might help?

switch(sortByString){
    case: "Id.NiNumber":
    SortByNiNumber(List<Person> listToSort);
    break;
    ...
}

if you don't have too many options it would be faster. And maybe you can replace the switch with a dictionary of search paths and delegates or actions.

answered Jul 01 '16 at 07:22

Emanuele Andreoli

31
7

I do it like that now. But this will have to work on any class and not just Person, and I need it to not have to write all sort expressions for all classes... – Beaker Jul 01 '16 at 07:39
Mmh... Guess you should give a bit more of background then. Usually, when i have to do something so "universal" the answer is just changing the point of view and rethink at it. – Emanuele Andreoli Jul 01 '16 at 07:42

score 0 · Accepted Answer · edited May 23 '17 at 12:32

You can modify the approach @E.Mourits linked: C# dynamic. String property path. I included a bit of error checking, on error you have to check the InnerException of the InvalidOperationException the Sort method can throw.

static void SortByAny<T>(List<T> list, string path)
{
    list.Sort((x, y) => ReflectOnPath(x, path).CompareTo(ReflectOnPath(y, path)));
}

static IComparable ReflectOnPath(object o, string path)
{
    object value = o;
    var pathComponents = path.Split('.');
    foreach (var component in pathComponents)
    {
        if (value == null)
        {
            throw new NullReferenceException($"Path '{path}' can not be resolved at: {component}.");
        }
        var prop = value.GetType().GetProperty(component);
        if (prop == null)
        {
            throw new ArgumentException($"Path '{path}' can not be resolved at: {component}.", nameof(path));
        }
        value = prop.GetValue(value, null);
    }
    if (!(value is IComparable))
    {
        throw new ArgumentException($"Value at path '{path}' does not implement ICompareable.", nameof(path));
    }
    return (IComparable)value;
}

If some of the values you want to compare do not implement IComparable you have to add more details how you want to compare them in this case.

Only issue with these kind of solutions is Performance. Dont believe there is much to optimize with this. — Beaker, Jul 01 '16 at 09:59

List.Sort by property name - Including subclasses

3 Answers3