Case insensitive group on multiple columns

Question

Is there anyway to do a LINQ2SQL query doing something similar to this:

var result = source.GroupBy(a => new { a.Column1, a.Column2 });

Answer 1

I've expanded on Bill B's answer to make things a little more dynamic to avoid "hardcoding" the column properties in the GroupKey and IQualityComparer<>.

private class GroupKey
    {
        public List Columns { get; } = new List();

        public GroupKey(params string[] columns)
        {
            foreach (var column in columns)
            {
                // Using 'ToUpperInvariant()' if user calls Distinct() after 
                // the grouping, matching strings with a different case will 
                // be dropped and not duplicated
                Columns.Add(column.ToUpperInvariant());
            }
        }

    }

    private class KeyComparer : IEqualityComparer
    {

        bool IEqualityComparer.Equals(GroupKey x, GroupKey y)
        {
            for (var i = 0; i < x.Columns.Count; i++)
            {
                if (!x.Columns[i].Equals(y.Columns[i], StringComparison.OrdinalIgnoreCase)) return false;
            }

            return true;
        }

        int IEqualityComparer.GetHashCode(GroupKey obj)
        {
            var hashcode = obj.Columns[0].GetHashCode();

            for (var i = 1; i < obj.Columns.Count; i++)
            {
                var column = obj.Columns[i];
                // *397 is normally generated by ReSharper to create more unique values
                // So I added it here, it's technically not required
                hashcode = (hashcode * 397) ^ (column != null ? column.GetHashCode() : 0);
            }

            return hashcode;
        }
    }

Usage:

var result = source.GroupBy(r => new GroupKey(r.Column1, r.Column2, r.Column3), new KeyComparer());

This way, you can pass any number of columns into the GroupKey constructor.