Linq to sql 我可以引用Linq to Sql查询中的计算列吗?
我有以下模式:Linq to sql 我可以引用Linq to Sql查询中的计算列吗?,linq-to-sql,Linq To Sql,我有以下模式: product - productID (PK) - name - units purchase - purchaseID (PF) - productID (FK) - soldUnits - woUnits boxContents - boxID (PK) - puchaseID (FK) - count 以及以下Linq到SQL查询: var qStockLevel = from pr in db.products
product
- productID (PK)
- name
- units
purchase
- purchaseID (PF)
- productID (FK)
- soldUnits
- woUnits
boxContents
- boxID (PK)
- puchaseID (FK)
- count
以及以下Linq到SQL查询:
var qStockLevel = from pr in db.products
select new
{
pr.productID,
pr.name,
totalUnits = (from pu in db.purchases
where pu.productID == pr.productID
select pu).Count() * pr.units,
sold = (from pr2 in db.products
join pu in db.purchases on pr.productID equals pu.productID into pp
where pr2.productID == pr.productID
from pu2 in pp.DefaultIfEmpty()
select (int?) pu2.soldUnits ?? 0).Sum(),
writtenOff = (from pr2 in db.products
join pu in db.purchases on pr.productID equals pu.productID into pp
where pr2.productID == pr.productID
from pu in pp.DefaultIfEmpty()
select (int?)pu.woUnits ?? 0).Sum(),
onDisplay = (from pr2 in db.products
join bc in db.boxContents on pr.productID equals bc.purchase.productID into bp
where pr2.productID == pr.productID
from bc in bp.DefaultIfEmpty()
select (int?)bc.count ?? 0).Sum(),
available = (totalUnits - sold - writtenOff - onDisplay),
};
末尾的“available”列不起作用,但我已经包含它来说明我试图实现的内容——一个根据已经生成的列计算的列。这可能吗?我可以在表示层进行,但我想先检查一下这是否可行
另外,在我(Linq新手)看来,当我重复生成writenoff和sell列时,查询看起来效率很低。当涉及聚合函数时,有没有更好的方法来实现这一点
谢谢
编辑
还有一件事-我只想返回“可用”大于0的行 对最后一行执行第二次select new{}(您必须再次复制第二次select中需要的所有字段),然后添加where子句
EDIT:虽然不太相关,但看起来您可以从一个包含可用值的新列中获益(使用Linq To Sql和InotityPropertyChange,这应该很容易实现)这里有一个查询,它可以满足您的需要 (注意:这假设您已经在DBML设计器中设置了
产品
->购买
->BoxContents
之间的关联。)
并且,仅供参考,这里有一种方法可以设置产品
类
(您可能希望使用来加载产品的子项。)
var query = from product in context.Products
where
(
product.Purchases.Count() * product.units -
product.Purchases.Sum(purchase => purchase.soldUnits ?? 0) -
product.Purchases.Sum(purchase => purchase.woUnits ?? 0) -
product.Purchases.SelectMany(purchase => purchase.BoxContents).Sum(bc => bc.count ?? 0)
) > 0
select product;
public partial class Product
{
public int TotalUnits
{
get { return this.Purchases.Count * this.units ?? 0; }
}
public int Sold
{
get { return this.Purchases.Sum(p => p.soldUnits ?? 0); }
}
public int WrittenOff
{
get { return this.Purchases.Sum(p => p.woUnits ?? 0); }
}
public int OnDisplay
{
get { return this.Purchases.SelectMany(p => p.BoxContents).Sum(b => b.count ?? 0); }
}
public int Available
{
get { return TotalUnits - Sold - WrittenOff - OnDisplay; }
}
}