使用 Linq 获取当前和上一个项目

我有一个 Offer 类，例如

public class Offer
{
    public int OfferID { get; set; }
    public DateTime OfferDate { get; set; }
    public int CustomerID { get; set; }
}

现在我有很多这样的优惠

List<Offer> oList = new List<Offer>();
oList.Add(new Offer() { OfferID = 1, OfferDate = new DateTime(2018, 01, 01), CustomerID = 1 });
oList.Add(new Offer() { OfferID = 2, OfferDate = new DateTime(2018, 01, 03), CustomerID = 1 });
oList.Add(new Offer() { OfferID = 3, OfferDate = new DateTime(2018, 01, 01), CustomerID = 2 });
oList.Add(new Offer() { OfferID = 4, OfferDate = new DateTime(2018, 01, 05), CustomerID = 2 });
oList.Add(new Offer() { OfferID = 5, OfferDate = new DateTime(2018, 01, 02), CustomerID = 1 });

我想按 ID 获取报价，同时也想按日期获取该客户之前的报价。

目前我正在使用 Linq2SQL 并进行两个选择。首先，我通过 ID 选择所需的 Offer，然后通过OfferDate.

示例：如果OfferID==5该客户之前的报价是OfferID==1.

public List<Offer> GetCurrentAndPrevious(int OfferID)
{
    using (DataContext cx = new DataContext())
    {
        Offer oCurrent = cx.Offer.Single(x => x.OfferID = OfferID);
        Offer oPrevious = cx.Offer.OrderBy(x => x.OfferDate)
                                  .Last(x => x.CustomerID = oCurrent.CustomerID && x.OfferDate < oCurrent .OfferDate);
        return new List<Offer>() { oCurrent , oPrevious };
    }
}

问题：有没有一种方法可以通过一次查询来解决这个问题，而不是查询数据库两次？

//query syntax
var data = (from curr in cx.Offer.Where(x => x.OfferID == OfferID)
            from prev in cx.Offer
            where curr.CustomerID == prev.CustomerID && curr.OfferDate >= prev.OfferDate
            orderby prev.OfferDate descending 
            select prev).Take(2).ToList();

//fluent syntax
data = cx.Offer.Where(x => x.OfferID == OfferID)
.Join(cx.Offer, curr => 0, prev => 0, (curr, prev) => new { curr, prev })
.Where(x => x.curr.CustomerID == x.prev.CustomerID && x.curr.OfferDate >= x.prev.OfferDate)
.OrderByDescending(x => x.prev.OfferDate)
.Select(x => x.prev).Take(2).ToList();

 return new List<Offer>() { data.FirstOrDefault(), data.Count == 2 ? data.Last() : null };