Map scalar values from Dapper rows to dto objects

.cs

	public static class IEnumerableExtension {
		public static IEnumerable<TFirst> Map<TFirst, TSecond, TKey>
		(
			this IEnumerable<TFirst> firstList,
			Func<TFirst, TKey> firstKey, 
			Func<TSecond, TKey> secondKey, 
			Action<TFirst, IEnumerable<TSecond>> addChildren,
			Func<IEnumerable<TSecond>> secondList
		)
		{
			var first = firstList.ToList();
			var childMap = secondList()
				.GroupBy(s => secondKey(s))
				.ToDictionary(g => g.Key, g => g.AsEnumerable());

			foreach (var item in first)
			{
				IEnumerable<TSecond> children;
				if(childMap.TryGetValue(firstKey(item), out children))
				{
					addChildren(item,children);
				}
			}

			return first;
		} 
    }
 
    var data = reader.Read<object>();

    collection.Map<DTO, object, int>(
        dto => dto.id,
        dict => Convert.ToInt32(((IDictionary<string, object>)dict)["seconddtoid"]),
        (dto, dict) => {
           dto.prop = Convert.ToInt32(((IDictionary<string, object>)(dict.First()))["likecount"]);
        },
        () => {
           return data;
        }
    );