linq 子查询加入和分组依据

Question

您好，是否可以将以下查询转换为 linq ？ ... 我正在使用实体框架核心并尝试使用存储过程，但似乎我必须创建一个适用于存储过程元数据的模型。所以我想了解这种查询是否可以翻译成 linq，所以我不必创建单独的数据库模型。

    SELECT 
    Stock.stockID ProductID, 
    stockName ProductName, 
    categoryName ProductCategory, 
    typeName ProductType, 
    sizeName ProductSize, 
    currentQuantity CurrentQuantity, 
    standardQuantity QuantityPerBox, 
    CONVERT(VARCHAR(255),CONVERT(INT,Stock.price)) AvgUnitCost,
    CONVERT(VARCHAR(255),CONVERT(INT,x.lastUnitCost)) LastOrderUnitCost,
    CONVERT(VARCHAR(10),CONVERT(DATE,x.lastOrderDate)) LastOrderDate
FROM dbo.Stock
LEFT JOIN 
(
SELECT stockID,unitPrice lastUnitCost ,orderDate lastOrderDate, ROW_NUMBER() OVER (PARTITION BY stockID ORDER BY orderDate DESC) rn FROM dbo.SalesOrder 
    JOIN dbo.SalesOrderDetail ON SalesOrderDetail.salesOrderID = SalesOrder.salesOrderID
WHERE customerID = @customerID AND salesStatus = 'S'
) x ON x.stockID = Stock.stockID AND rn = 1
LEFT JOIN dbo.StockCategory ON StockCategory.stockCategoryID = Stock.stockCategoryID
LEFT JOIN dbo.StockType ON StockType.stockTypeID = Stock.stockTypeID
LEFT JOIN dbo.StockSize ON StockSize.stockSizeID = Stock.stockSizeID
WHERE disStock = 0

Answer 1

几乎一切皆有可能。你只需要注意性能。

var query = 
    from stock in db.Stocks
    join x in (
      from grp in (
        from so in db.SalesOrders
        join sod in db.SalesOrderDetails on so.SalesOrderId equals sod.SalesOrderId
        where so.CustomerId == customerId && so.SalesStatus == "S"
        orderby so.OrderDate descending
        select new {
            sod.StockId, 
            LastUnitCost = sod.UnitPrice,
            LastOrderDate = so.OrderDate
        } into inner
        group inner by inner.StockId)
      select grp.Take(1)) on x.StockId equals stock.StockId into lastStockSales
    from x in lastStockSales.DefaultIfEmpty()
    join sc in db.StockCategories on stock.StockCatergotyId equals sc.StockCategoryId into scLeft
    from sc in scLeft.DefaultIfEmpty()
    join st in db.StockTypes on stock.StockTypeId equals st.StockTypeId into stLeft
    from st in stLeft.DefaultIfEmpty()
    join ss in db.StockSizes on stock.StockSizeId equals ss.StockSizeId into ssLeft
    from ss in ssLeft.DefaultIfEmpty()
    where stock.DisStock == 0
    select new MyDTO {
      ProductId = stock.StockId,
      ProductName = stock.StockName,
      ProductType = st.TypeName,
      ProductSize = ss.SizeName,
      CurrentQuantity = stock.CurrentQuantity,
      QuantityPerBox = stock.StandardQuantity,
      AvgUnitCost = stock.Price,
      LastOrderUnitCost = x.LastUnitCost,
      LastOrderDate = x.LastOrderDate
    };

正如您所见，重写这些查询很容易，我不得不稍微更改一下有关如何获取库存商品最新销售的逻辑，因为从 LINQ 的角度来看，ROW_NUMBER() OVER (PARTITION... 不受支持。同样，您必须在重写查询时考虑性能。

希望这会有所帮助。