我如何使用（在LINQ中选择方法？

Question

我如何在linq中编写“ in（select） ”方法？

我正在尝试转换：

UPDATE ActualAmountsByLocation SET isCustomerItem=1 WHERE ItemBarcode IN (SELECT barcode FROM StockMaterials WHERE barcode=@Barcode AND ownership=1)

我已经试过像这样：

    Array stockMaterials = ( from s in stockMovementCtx.StockMaterials where s.barcode == Barcode && s.ownership ==1 select s).ToArray();
                           actualAmountsByLocation = (from a in stockMovementCtx.ActualAmountsByLocations
                                                       where a.ItemBarcode.Contains(stockMaterials)
                                                      select a).First();

Answer 1

要获得IN查询，您需要反转包含的含义。 同样，也不需要实现第一个查询IMO。

var stockMaterials = from s in stockMovementCtx.StockMaterials
                     where s.barcode == Barcode && s.ownership ==1
                     select s;
actualAmountsByLocation = (from a in stockMovementCtx.ActualAmountsByLocations
                           where stockMaterials.Contains( a.ItemBarcode)
                           select a).First();

Answer 2

你快到了。 删除.ToArray调用以防止直接执行查询，并使stockMaterials变量的类型为IQueryable<StockMaterial> 。

Answer 3

这是您要找的东西吗？

ActualAmountsByLocation = StockMaterials.Where(s => s.barcode == Barcode && s.ownership == 1).ToArray();

Answer 4

    var stockMaterials = (from s in stockMovementCtx.StockMaterials
                          where s.barcode == Barcode && s.ownership == 1
                          select s).ToArray();
    var actualAmountsByLocation = (from a in stockMovementCtx.ActualAmountsByLocations
                                   where stockMaterials.Contains(a.ItemBarcode)
                                   select a).First();

Answer 5

希望下面的代码示例对您有所帮助

// these are using linq methods
var barcodes = stockMovementCtx.StockMaterials
                 .Where(s => s.barcode == Barcode && s.ownership == 1)
                 .Select(s => s.barcode);
var amounts = stockMovementCtx.ActualAmountsByLocations
                .Where(a => barcodes.Contains(a.ItemBarCode))
                .FirstOrDefault();
// if you would like to use the query expressions instead, here they are
//var barcodes = from s in stockMovementCtx.StockMaterials
//               where s.barcode = Barcode && s.ownership == 1
//               select s.barcode;
//var amounts = (from a in stockMovementCtx.ActualAmountsByLocations
//              where barcodes.Contains(a.ItemBarCode.Contains)
//              select a).FirstOrDefault();

// helpful to use FirstOrDefault if you are not sure that the query will return a result
if (amounts != null) {
  // change value
  amounts.IsCustomerItem = 1;
  // update database
  stockMovementCtx.SubmitChanges();
}

Answer 6

在LinQ上进行更新非常容易，例如，请查看下面的代码块。

var user = (from s in dataContext.USERS

调用用户表，并设置条件。

where s.UserId.Equals(id) select s).FirstOrDefault();

我想在用户电子邮件上进行更改。（请不要忘记：如果使用ToList（）进行调用，则需要控制列表计数以避免ex的异常：if（user.Count> 0）。）

更新用户：

s.EmailAddress = serkan@serkanhekimoglu.com;
dataContext.SubmitChanges();

并且您的数据将在SubmitChanges（）之后更新；