Question

我正在尝试从linq查询中获取匹配项 -

 public ActionResult TagFilter(TagModel tag) {
        List<CardModel> cardlist = null;
        var cardtaglist = (from u in db.CardTagTables
                           where u.CardTagName == tag.tagName
                           select u).ToList();
        cardlist = (from u in db.CardTables
                    where u.CardID == cardtaglist.Where(e=>e.FKCardTagID==u.CardID)
                    select new CardModel {
                        cardHashCode = tag.tagName,
                        cardDate = u.CardDate,
                        cardFileName = u.CardFileName,
                        cardFilePath = u.CardFilePath,
                        cardID = u.CardID,
                        cardTitle = u.CardTitle
                    }).ToList();
        if (cardlist.Count == 0) {
            return Json(new { success = false });
        }
        else {
            return PartialView("_FunHomePartial", cardlist);
        }

    }

tag=>tagName的匹配来自列表cardtaglist。

我的行中出现Cannot implicitly convert type int to bool错误 -

  where u.CardID == cardtaglist.Where(e=>e.FKCardTagID==u.CardID)

如何匹配列表cardtaglist中的元素？

Answer 1

如何更换

u.CardID == cardtaglist.Where(e=>e.FKCardTagID==u.CardID)

带

cardtaglist.Any(e=>e.FKCardTagID==u.CardID)

Answer 2

首先，如果您只使用CardTagTable，为什么选择所有FKCardTagID实体！？最好的方法 - 只选择必填字段：

var cardtagIds = (from u in db.CardTagTables
                  where u.CardTagName == tag.tagName
                  select u.FKCardTagID).ToList();

关于您的错误，您需要将IQueriable与数值进行比较。在这种情况下，您可以使用Contains方法：

cardlist = (from u in db.CardTables.Where(u => cardtagIds.Contains(u.CardID));
            select new CardModel {
            ....

修改

此外，可以优化此查询：

cardlist = (from u in db.CardTables.Where(u => db.CardTagTables .Where(ct => ct.CardTagName == tag.tagName) .Select(ct => ct.FKCardTagID) .Contains(u.CardID)) select new CardModel { ....

Answer 3

使用：

   var result=cardtaglist.Any(e=>e.FKCardTagID==u.CardID)

从列表中选择linq

3 个答案: