LineExtensions.cs

public static class LinqExtensions
{
    public static IQueryable<T> QueryIfElse<T>(this IQueryable<T> query,
            Func<bool> predicate,
            Func<IQueryable<T>, IQueryable<T>> @if,
            Func<IQueryable<T>, IQueryable<T>> @else) =>
        predicate() ? @if(query) : @else(query);
}