WhereIf 扩展

public static class QueryableExtensions
{
    public static IQueryable<T> WhereIf<T>(this IQueryable<T> query, bool condition, Expression<Func<T, bool>> predicate)
    {
        return condition ? query.Where(predicate) : query;
    }

    public static IQueryable<T> WhereIf<T>(this IQueryable<T> query, bool condition, Expression<Func<T, int, bool>> predicate)
    {
        return condition ? query.Where(predicate) : query;
    }

    public static IEnumerable<T> WhereIf<T>(this IEnumerable<T> query, bool condition, Func<T, bool> predicate)
    {
        return condition ? query.Where(predicate) : query;
    }
}