Method Sum<TKey, TProps, TValue>(IRedbGrouping<TKey, TProps>, Expression<Func<TProps, TValue>>)

Sum in a group: Agg.Sum(g, x => x.Stock)

public static TValue Sum<TKey, TProps, TValue>(IRedbGrouping<TKey, TProps> group, Expression<Func<TProps, TValue>> selector) where TProps : class, new()