C# LINQ, dynamic grouping by [Key] attributes

Question

Consider the following classes:

public class Potato
{
    [Key]
    public string Farm { get; set; }
    [Key]
    public int Size { get; set; }
    public string Trademark { get; set; }
}

public class Haybell
{
    [Key]
    public string color { get; set; }
    public int StrawCount { get; set; }
}

public class Frog
{
    [Key]
    public bool IsAlive { get; set; }
    [Key]
    public bool IsVirulent { get; set; }
    public byte LimbCount { get; set; } = 4;
    public ConsoleColor Color { get; set; }
}

Each class has properties with [Key] attribute. Is it possible to dynamically group an IEnumerable of any of these classes by their respective [Key] attributes?

Answer 1

Somebody had posted a valid answer and removed it later for some reason. Here it is:

Combined key class:

class CombinedKey<T> : IEquatable<CombinedKey<T>>
{
    readonly object[] _keys;

    public bool Equals(CombinedKey<T> other)
    {
        return _keys.SequenceEqual(other._keys);
    }

    public override bool Equals(object obj)
    {
        return obj is CombinedKey<T> key && Equals(key);
    }

    public override int GetHashCode()
    {
        int hash = _keys.Length;
        foreach (object o in _keys)
        {
            if (o != null)
            {
                hash = hash * 13 + o.GetHashCode();
            }
        }
        return hash;
    }

    readonly Lazy<Func<T, object[]>> lambdaFunc = new Lazy<Func<T, object[]>>(() =>
    {
        Type type = typeof(T);
        var paramExpr = Expression.Parameter(type);
        var arrayExpr = Expression.NewArrayInit(
            typeof(object),
            type.GetProperties()
                .Where(p => (Attribute.GetCustomAttribute(p, typeof(KeyAttribute)) != null))
                .Select(p => Expression.Convert(Expression.Property(paramExpr, p), typeof(object)))
                .ToArray()
            );

        return Expression.Lambda<Func<T, object[]>>(arrayExpr, paramExpr).Compile();
    }, System.Threading.LazyThreadSafetyMode.PublicationOnly);

    public CombinedKey(T instance)
    {
        _keys = lambdaFunc.Value(instance);
    }
}

Caller function and the actual usage:

public static class MyClassWithLogic
{
    //Caller to CombinedKey class
    private static CombinedKey<Q> NewCombinedKey<Q>(Q instance)
    {
        return new CombinedKey<Q>(instance);
    }

    //Extension method for IEnumerables
    public static IEnumerable<T> DistinctByPrimaryKey<T>(this IEnumerable<T> entries) where T : class
    {
        return entries.AsQueryable().GroupBy(NewCombinedKey)
            .Select(r => r.First());
    }
}

Yes, it is relatively slow, so if it is a problem, then Klaus Gütter's solutions are the way to go.