Как мне написать этот запрос кросс-таблицы в Linq (предоставлены таблицы и данные)

Question

Это простой вид кросс-таблицы.У меня возникают трудности с передачей моих знаний по SQL в Linq, и из-за того, что его сложно протестировать (я не получил linqpad, работающий должным образом для разработки WP7), я действительно не могу легко "играть".

CREATE TABLE Store
(
    StoreID INT NOT NULL,
    StoreName VARCHAR(10) NOT NULL
)

INSERT INTO Store (StoreID,StoreName) VALUES (1,'Store A')
INSERT INTO Store (StoreID,StoreName) VALUES (2,'Store B')

CREATE TABLE ProductType
(
    ProductTypeID INT NOT NULL,
    ProductTypeName VARCHAR(20) NOT NULL
)

INSERT INTO ProductType (ProductTypeID,ProductTypeName) VALUES (1,'Clothing')
INSERT INTO ProductType (ProductTypeID,ProductTypeName) VALUES (2,'Food')

CREATE TABLE Product
(
    ProductID INT NOT NULL,
    ProductTypeID INT NOT NULL,
    ProductName VARCHAR(20) NOT NULL
)

INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (1,1,'Hat')
INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (2,1,'Shirt')
INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (3,1,'Pant')
INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (4,2,'Orange')
INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (5,2,'Apple')


CREATE TABLE Purchase
(
    PurchaseID INT NOT NULL,
    ProductID INT NOT NULL,
    StoreID INT NOT NULL,
    Quantity INT NULL,
    Amount INT NULL
)

INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (1,1,1,5,10)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (2,2,1,4,12)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (3,3,1,1,10)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (4,4,1,3,16)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (5,5,1,7,12)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (6,1,2,10,22)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (7,2,2,8,26)


SELECT s.StoreName
    ,SUM(CASE
        WHEN t.ProductTypeID=1 THEN Amount
        ELSE 0
    END ) as ClothingAmount
    ,SUM(CASE
        WHEN t.ProductTypeID=2 THEN Amount
        ELSE 0
    END )AS FoodQuantity
    ,SUM(CASE
        WHEN t.ProductTypeID=1 THEN Quantity
        ELSE 0
    END ) as ClothingAmount
    ,SUM(CASE
        WHEN t.ProductTypeID=2 THEN Quantity
        ELSE 0
    END )AS FoodQuantity
FROM Purchase u
INNER JOIN Product r
ON u.ProductID=r.ProductID
INNER JOIN ProductType t
ON r.ProductTypeID=t.ProductTypeID
INNER JOIN Store s
ON s.StoreID=u.StoreID
GROUP BY s.StoreName

Answer 1

Ниже приведен перевод 1: 1 вашего оператора SQL-запроса в LINQ:

from u in Purchases
join r in Products on u.ProductID equals r.ProductID
join t in ProductTypes on r.ProductTypeID equals t.ProductTypeID
join s in Stores on u.StoreID equals s.StoreID
group new {Purchase = u, Product = r, ProductType = t, Store = s} by s.StoreName into grouped
select new {
    StoreName = grouped.Key,
    ClothingAmount = grouped.Sum(entry => entry.ProductType.ProductTypeID == 1 ? entry.Purchase.Amount : 0),
    FoodAmount = grouped.Sum(entry => entry.ProductType.ProductTypeID == 2 ? entry.Purchase.Amount : 0),
    ClothingQuantity = grouped.Sum(entry => entry.ProductType.ProductTypeID == 1 ? entry.Purchase.Quantity : 0),
    FoodQuantity = grouped.Sum(entry => entry.ProductType.ProductTypeID == 2 ? entry.Purchase.Quantity : 0)
}

, который переводится в следующий SQL:

SELECT SUM(
    (CASE 
        WHEN [t2].[ProductTypeID] = @p0 THEN [t0].[Amount]
        ELSE @p1
     END)) AS [ClothingAmount], SUM(
    (CASE 
        WHEN [t2].[ProductTypeID] = @p2 THEN [t0].[Amount]
        ELSE @p3
     END)) AS [FoodAmount], SUM(
    (CASE 
        WHEN [t2].[ProductTypeID] = @p4 THEN [t0].[Quantity]
        ELSE @p5
     END)) AS [ClothingQuantity], SUM(
    (CASE 
        WHEN [t2].[ProductTypeID] = @p6 THEN [t0].[Quantity]
        ELSE @p7
     END)) AS [FoodQuantity], [t3].[StoreName]
FROM [Purchase] AS [t0]
INNER JOIN [Product] AS [t1] ON [t0].[ProductID] = [t1].[ProductID]
INNER JOIN [ProductType] AS [t2] ON [t1].[ProductTypeID] = [t2].[ProductTypeID]
INNER JOIN [Store] AS [t3] ON [t0].[StoreID] = [t3].[StoreID]
GROUP BY [t3].[StoreName]

Обратите внимание, однако, что настоятельно рекомендуется установить в таблицах правильный первичный и внешний ключи. Как только это будет сделано (и Модель соответствующим образом обновлена), тот же запрос может быть уменьшен до:

from purchase in Purchases
group purchase by purchase.Store.StoreName into grouped
select new {
    StoreName = grouped.Key,
    ClothingAmount = grouped.Sum(purchase => purchase.Product.ProductTypeID == 1 ? purchase.Amount : 0),
    FoodAmount = grouped.Sum(purchase => purchase.Product.ProductTypeID == 2 ? purchase.Amount : 0),
    ClothingQuantity = grouped.Sum(purchase => purchase.Product.ProductTypeID == 1 ? purchase.Quantity : 0),
    FoodQuantity = grouped.Sum(purchase => purchase.Product.ProductTypeID == 2 ? purchase.Quantity : 0)
}