Question

I have already thought about how I’m going to solve this by rolling my own solution, but I wondered if .NET already has the functionality for what I’m trying to acheive – if so, I’d rather use something built-in.

Suppose I have two instances of a Widget object, let’s call them PartA and PartB. The information from each has been garnered from two different web services, but both have matching IDs.

PartA
{
    ID: 19,
    name: "Percy",
    taste: "",
    colour: "Blue",
    shape: "",
    same_same: "but different"
}

PartB
{
    ID: 19,
    name: "",
    taste: "Sweet",
    colour: "",
    shape: "Hexagon",
    same_same: "but not the same"
}

I want to merge these to create the following:

Result
{
    ID: 19,
    name: "Percy",
    taste: "Sweet",
    colour: "Blue",
    shape: "Hexagon",
    same_same: "but different"
}

Notice how the value for same_same differs between each, but we consider PartA the master, so the result retains the value but different.

Now to complicate matters:

Suppose we have two lists:

List<Widget> PartA = getPartA();
List<Widget> PartB = getPartB();

Now here’s some pseudocode describing what I want to do:

List<Widget> Result = PartA.MergeWith(PartB).MergeObjectsOn(Widget.ID).toList();

Answer 1

You could write your own extension method(s), something like this:

static class Extensions
{
    public static IEnumerable<T> MergeWith<T>(this IEnumerable<T> source, IEnumerable<T> other) where T : ICanMerge
    {
        var otherItems = other.ToDictionary(x => x.Key);
        foreach (var item in source)
        {
            yield return (T)item.MergeWith(otherItems[item.Key]);
        }
    }
    public static string AsNullIfEmpty(this string s)
    {
        if (string.IsNullOrEmpty(s))
            return null;
        else
            return s;
    }
}

Where ICanMerge is like:

public interface ICanMerge
{
    object Key { get; }
    ICanMerge MergeWith(ICanMerge other);
}

Implemented e.g. like:

public class Widget : ICanMerge
{
    object ICanMerge.Key { get { return this.ID; } }
    int ID {get;set;}
    string taste {get;set;}
    public ICanMerge MergeWith(ICanMerge other)
    {
        var merged = new Widget();
        var otherWidget = (Widget)other;
        merged.taste = this.taste.AsNullIfEmpty() ?? otherWidget.taste;
        //...
        return merged;
    }
}

Then it’s as simple as PartA.MergeWith(PartB).ToList().