list 属性字段直接转成字符串数组

List<Car> cars = //whatever;
string concat = String.Join(",", cars.Select(c => c.Name).ToArray());

string concat = cars.Select(c => c.Name).Aggregate(new StringBuilder(), (sb, current) =>
{
    return sb.Length == 0 ? sb.Append(current) : sb.AppendFormat(",{0}", current);
}).ToString();