C#•4mo ago

How to implement alternative items. A is alt. to B and C => B alt. to A and C, etc.

How is this usually designed? An item with alternative items. For example B is alternative to A. That means A is alternative to B too. If I create C alternative to A, A and B become alternatives to C. Each one is an alternative to each other. Now imagine you have a tab for each (A, B, C) where you have the rows of alternatives. A Sync service has to update each tab when an alternative is added anywhere in the tabs. How would you implement this at the db or object level?

18 Replies

Joschi•4mo ago

I'm not entirely sure what you mean by "Alternative Item". But it sounds a bit like you need an abstract base class and then handle each inheriting type individually on the UI level. In the database you can just use a "table per hierarchy mapping". If you use EFCore it can handle that for you and there is a lot of documentation out there on how to do that.

Sygmond•4mo ago

currently is implemented like this

using System;
using System.Collections.Generic;
                    
public class Program
{
    public static void Main()
    {
        // we have 3 items: A, B and C
        var a = new Item {Name = "A"};
        var b = new Item {Name = "B"};
        var c = new Item {Name = "C"};
        
        var items = new List<Item>()
        {
            a,
            b,
            c,
        };
        
        // add B as an alternative to A
        a.Alternatives.Add(b);
        
        // that means A is an alternative to B
        b.Alternatives.Add(a);
        
        // add C as an alternative to B
        b.Alternatives.Add(c);
        
        // that means B is an alternative to C
        c.Alternatives.Add(b);
        
        // and now the complication: it means that C is an alternative to A too, because A is alternative to B
        a.Alternatives.Add(c);
        
        // and it means A is an alternative to C too
        c.Alternatives.Add(a);

        // let's print the alternatives
        foreach(var item in items)
        {
            Console.Write($"Item {item.Name} has the alternatives: ");
            
            foreach(var alternative in item.Alternatives)
            {
                Console.Write($"{alternative.Name} ");
            }
            
            Console.WriteLine();
        }
        
        // Result:
        // Item A has the alternatives: B C 
        // Item B has the alternatives: A C 
        // Item C has the alternatives: B A 

        // then... trying to add/remove numerous alternatives... 
        // would make all thing way to complicated to sync all item.Alternatives in each
    }
}

public class Item 
{
  public string Name {get; set;}
  public List<Item> Alternatives {get; set;} = new();
}

using System;
using System.Collections.Generic;
                    
public class Program
{
    public static void Main()
    {
        // we have 3 items: A, B and C
        var a = new Item {Name = "A"};
        var b = new Item {Name = "B"};
        var c = new Item {Name = "C"};
        
        var items = new List<Item>()
        {
            a,
            b,
            c,
        };
        
        // add B as an alternative to A
        a.Alternatives.Add(b);
        
        // that means A is an alternative to B
        b.Alternatives.Add(a);
        
        // add C as an alternative to B
        b.Alternatives.Add(c);
        
        // that means B is an alternative to C
        c.Alternatives.Add(b);
        
        // and now the complication: it means that C is an alternative to A too, because A is alternative to B
        a.Alternatives.Add(c);
        
        // and it means A is an alternative to C too
        c.Alternatives.Add(a);

        // let's print the alternatives
        foreach(var item in items)
        {
            Console.Write($"Item {item.Name} has the alternatives: ");
            
            foreach(var alternative in item.Alternatives)
            {
                Console.Write($"{alternative.Name} ");
            }
            
            Console.WriteLine();
        }
        
        // Result:
        // Item A has the alternatives: B C 
        // Item B has the alternatives: A C 
        // Item C has the alternatives: B A 

        // then... trying to add/remove numerous alternatives... 
        // would make all thing way to complicated to sync all item.Alternatives in each
    }
}

public class Item 
{
  public string Name {get; set;}
  public List<Item> Alternatives {get; set;} = new();
}

https://dotnetfiddle.net/rJQSRv

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Test your C# code online with .NET Fiddle code editor.

Sygmond•4mo ago

This is what it was designed by someone else. I proposed to my PM a simpler solution. Initially I was ignored and now the whole thing got to complicated. Looking forward to see what other people have in mind, without clouding them with my solution.

Joschi•4mo ago

So alternatives always go both ways?

Sygmond•4mo ago

yes

Joschi•4mo ago

Is the path of interest? What I mean is, do you need to know that A is an alternative to C, because both are an alternative to B?

Sygmond•4mo ago

Yes. Each item needs to have complete list of alternatives, so every new alternative item added, the synchronization needs to be done again and add in each item the new alternative

Joschi•4mo ago

That didn't answer the question. Do you just need to know that A is an alternative to C, or is the information important that A is an alternative to C, because both are alternatives to B. Basically is there a difference between something being a direct alternative or indirect one.

Sygmond•4mo ago

No, I just need to know that A is an alternative to C If I add D as alternative to A, D will be alternative to all. Is not important in the UI why. I just need to list/print the alternatives of each. each item has its own tab with a grid where all alternatives for that item is listed

Joschi•4mo ago

Then what is the problem with stuffing them all into a simple list?

Sygmond•4mo ago

like in my example? the problem is if I add D to the list of A, that D needs to be added to the rest of the items.Alternatives you have to check each item where A is an alternative and add D and to D add the item that you just checked

Joschi•4mo ago

No just have a single list containing A B and C. And if D comes into the mix add it to that single list

Sygmond•4mo ago

and each item would have an id that points to that list? what I proposed is grouping, because this is esentially groups

Sygmond•4mo ago

https://dotnetfiddle.net/y0UUqw

C# Online Compiler | .NET Fiddle

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Joschi•4mo ago

Yes you could do that

Sygmond•4mo ago

assign a groupId to the ones you want to be alternatives and done

Joschi•4mo ago

Unless you need to recalculate the groups often that also works fine. (If it's all stored in a DB that's less of a concern)

Sygmond•4mo ago

yes, is in the DB, but is loaded in the memory (UI) and if a new item is added in any alternative group, is tracked and saved separately. but with a group or a list like you said, is way simpler than the current implementation

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How to implement alternative items. A is alt. to B and C => B alt. to A and C, etc.