使用Join在LINQ中實現where子句

Question

我有這個LINQ（LINQ TO ENTITY）：

var clientFullReview = (from cr in clientReview
                        join ir in inspectionReviews on cr.siteId equals ir.SiteId into g
                        from subsite in g.DefaultIfEmpty()
                        select new
                        {
                         clientId = cr.clientId,
                         clientName = cr.clientName,
                         siteId = cr.siteId == null ? -1 : cr.siteId,
                         inspectionReviewId = (subsite == null ? -1 : subsite.Id),
                         inspectionFrequency = (subsite == null ? -1 : subsite.FrequencyId),

                          isNormal = (subsite == null ? false : subsite.IsNormal)
                         });

在上面的鏈接中，我需要使用where子句。

inspectionReviews-具有日期屬性。 在LINQ上方，我只想加入具有特定日期的inspectionReviews記錄，例如：

    var clientFullReview = (from cr in clientReview
                            join ir in inspectionReviews on cr.siteId equals
                            where ir.DateReview.Year == date.Year &&
                            ir.DateReview.Month == date.Month 
                            into g
                            from subsite in g.DefaultIfEmpty()
                            select new
                            {
                             clientId = cr.clientId,
                             clientName = cr.clientName,
                             siteId = cr.siteId == null ? -1 : cr.siteId,
                             inspectionReviewId = (subsite == null ? -1 : subsite.Id),
                             inspectionFrequency = (subsite == null ? -1 : subsite.FrequencyId),

                              isNormal = (subsite == null ? false : subsite.IsNormal)
                             });

但是，當我嘗試使用where子句實現它時，出現此錯誤：

A query body must end with a select clause or a group clause

關於這個關鍵詞： into第二個LINQ。

所以我的問題是在實現連接時如何按日期過濾數據？

Answer 1

單程

join ir in inspectionReviews.Where(x =>
    x.DateReview.Year == date.Year && x.DateReview.Month == date.Month)
on cr.siteId equals ir.SiteId

其他方式

join ir in (from x in inspectionReviews
    where x.DateReview.Year == date.Year && x.DateReview.Month == date.Month
    select x)
on cr.siteId equals ir.SiteId

另一種方式

join ir on cr.siteId equals ir.SiteId into g
from subsite in g
    .Where(x => x.DateReview.Year == date.Year && x.DateReview.Month == date.Month)
    .DefaultIfEmpty()

Answer 2

Join子句只允許等於，因此，如果需要過濾聯接的集合，則可以在第二個from子句下使用subsite變量：

join ir in inspectionReviews on cr.siteId equals ir.SiteId
into g
from subsite in g.DefaultIfEmpty()
where subsite.DateReview.Year == date.Year &&
subsite.DateReview.Month == date.Month 

Answer 3

將其分為兩個查詢，然后從最篩選的第一個列表中進行第二個選擇。

我不會重現您的代碼，因為我認為第二個聯接值上缺少一些文本，但是我們的想法是分兩個步驟完成：

 var clientFullReviews = (from cr in clientReview
                        join ir in inspectionReviews on cr.siteId equals
                        where ir.DateReview.Year == date.Year &&
                        ir.DateReview.Month == date.Month 
                        into g

 var clientcurrent reviews =(from cr clientFullReviews select new
                        {
                         clientId = cr.clientId,
                         clientName = cr.clientName,
                         siteId = cr.siteId == null ? -1 : cr.siteId,
                         inspectionReviewId = (subsite == null ? -1 : subsite.Id),
                         inspectionFrequency = (subsite == null ? -1 : subsite.FrequencyId),

                          isNormal = (subsite == null ? false : subsite.IsNormal)
                         });

這不是完美的語法，因為我不太了解您的數據對象，但是您明白了。 我不確定您是否會因此受到性能的影響，但是我幾乎總是這樣將其拆開，以保持Linq語法的整潔和可讀性（並避免在一行中將太多擴展表達式與自己混淆！）