實體框架多對多查詢生成粗糙SQL

Question

我正在處理一個委託跟蹤系統。業務案例需要銷售人員和客戶之間的多對多關係。 （簡化）實體是：

public class Customer { 
    public int Id { get; set; } 
    public string Name { get; set; } 

    public virtual ICollection<CustomerSeller> CustomerSellers { get; set; } 
    public virtual ICollection<Payment> Payments { get; set; } 
} 

public class Seller { 
    public int Id { get; set; } 
    public string Name { get; set; } 
    public virtual ICollection<CustomerSeller> CustomerSellers { get; set; } 
} 

// join table w/payload for many-to-many relationship 
public class CustomerSeller { 
    public int Id { get; set; } 
    public Seller Seller { get; set; } 
    public Customer Customer { get; set; } 
    public decimal CommissionRate { get; set; } 
} 

public class Payment { 
    public int Id { get; set; } 
    public Customer ReceivedFrom { get; set; } 
    public DateTime Date { get; set; } 
    public decimal Amount { get; set; } 
} 

我一時目標是讓客戶的所有付款鏈接到特定銷售人員的名單。如果我寫直接的SQL它會是這個樣子：

select Payment.* 
from Payment 
inner join CustomerSeller on CustomerSeller.Customer_Id = Payment.ReceivedFrom_Id 
where CustomerSeller.Seller_Id = @sellerIdToQuery 

我使用LINQ/EF想這對我的ASP NET MVC的網站使用此代碼：

public ActionResult Sales(int id) { 
    var qry = (
    from p in db.Payments 
    join cs in db.CustomerSellers on p.ReceivedFrom equals cs.Customer 
    where cs.Seller.Id == id 
    select p); 
    var paymentList = qry.ToList(); 
    return View(paymentList); 
} 

這並不工作，但幕後的SQL看起來waaay複雜（這是出乎我的SQL解碼能力來分析）：

{SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[Date] AS [Date], 
[Extent1].[Amount] AS [Amount], 
[Extent1].[ReceivedFrom_Id] AS [ReceivedFrom_Id] 
FROM [dbo].[Payment] AS [Extent1] 
INNER JOIN [dbo].[CustomerSeller] AS [Extent2] ON EXISTS (SELECT 
    1 AS [C1] 
    FROM  (SELECT 1 AS X) AS [SingleRowTable1] 
    LEFT OUTER JOIN (SELECT 
     [Extent3].[Id] AS [Id] 
     FROM [dbo].[Customer] AS [Extent3] 
     WHERE [Extent1].[ReceivedFrom_Id] = [Extent3].[Id]) AS [Project1] ON 1 = 1 
    LEFT OUTER JOIN (SELECT 
     [Extent4].[Id] AS [Id] 
     FROM [dbo].[Customer] AS [Extent4] 
     WHERE [Extent2].[Customer_Id] = [Extent4].[Id]) AS [Project2] ON 1 = 1 
    LEFT OUTER JOIN (SELECT 
     [Extent5].[Id] AS [Id] 
     FROM [dbo].[Customer] AS [Extent5] 
     WHERE [Extent1].[ReceivedFrom_Id] = [Extent5].[Id]) AS [Project3] ON 1 = 1 
    LEFT OUTER JOIN (SELECT 
     [Extent6].[Id] AS [Id] 
     FROM [dbo].[Customer] AS [Extent6] 
     WHERE [Extent2].[Customer_Id] = [Extent6].[Id]) AS [Project4] ON 1 = 1 
    WHERE ([Project1].[Id] = [Project2].[Id]) OR (([Project3].[Id] IS NULL) AND ([Project4].[Id] IS NULL)) 
) 
WHERE [Extent2].[Seller_Id] = @p__linq__0} 

我什麼格式錯誤我的LINQ查詢（我是新）特別感興趣..怎麼寫呢？或者我的實體結構有問題嗎？或者SQL很好，並且可以在生產環境中高效運行大量數據？

進展情況：

首先，Slauma提出了兩個新的查詢。在對它們進行實驗時，我注意到SQL在處理Customer和Customer字段的連接表CustomerSeller上付出了額外的努力。這是我的錯誤，因爲這些字段應該是不可空的。我將它們設置爲[必填]在實體：

public class CustomerSeller { 
    public int Id { get; set; } 
    [Required] 
    public Seller Seller { get; set; } 
    [Required] 
    public Customer Customer { get; set; } 
    public decimal CommissionRate { get; set; } 
} 

第一個查詢Slauma寫道：

var qry = from p in db.Payments 
      where p.ReceivedFrom.CustomerSellers.Any(cs => cs.Seller.Id == id) 
      select p; 

產生了大大優於SQL：

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[Date] AS [Date], 
[Extent1].[Amount] AS [Amount], 
[Extent1].[ReceivedFrom_Id] AS [ReceivedFrom_Id] 
FROM [dbo].[Payment] AS [Extent1] 
WHERE EXISTS (SELECT 
    1 AS [C1] 
    FROM [dbo].[CustomerSeller] AS [Extent2] 
    WHERE ([Extent1].[ReceivedFrom_Id] = [Extent2].[Customer_Id]) AND ([Extent2].[Seller_Id] = @p__linq__0) 
) 

下TWEAK Slauma建議是加入我的原始查詢的Id字段，而不是整個實體：

var qry = from p in db.Payments 
      //old: join cs in db.CustomerSellers on p.ReceivedFrom equals cs.Customer 
      //new: 
       join cs in db.CustomerSellers on p.ReceivedFrom.Id equals cs.Customer.Id 
      where cs.Seller.Id == id 
      select p; 

這會產生一個非常高品質的SQL語句：

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[Date] AS [Date], 
[Extent1].[Amount] AS [Amount], 
[Extent1].[ReceivedFrom_Id] AS [ReceivedFrom_Id] 
FROM [dbo].[Payment] AS [Extent1] 
INNER JOIN [dbo].[CustomerSeller] AS [Extent2] ON [Extent1].[ReceivedFrom_Id] = [Extent2].[Customer_Id] 
WHERE [Extent2].[Seller_Id] = @p__linq__0 

本質是什麼，我會在SQL直接寫我自己。

小貼士：

（1）加入上的按鍵，而不是完整的實體。 （2）如果連接表不能包含多對多映射字段的空值，請將它們標記爲[必需]，這會簡化查詢。 （3）檢查linq查詢的幕後SQL，特別是在經常使用或者他們可能會觸及大量數據的情況下。可能有怪物躲藏。

（4）Slauma是一位紳士和學者。:-)

Answer 1

我會寫的查詢是這樣的：

var qry = from p in db.Payments 
      where p.ReceivedFrom.CustomerSellers.Any(cs => cs.Seller.Id == id) 
      select p; 
var paymentList = qry.ToList(); 

或完全地被擴展方法：

var qry = db.Payments 
    .Where(p => p.ReceivedFrom.CustomerSellers.Any(cs => cs.Seller.Id == id)); 
var paymentList = qry.ToList(); 

我不知道，有多少的SQL將從不同您的查詢。

編輯

備選：

var qry = db.CustomerSellers 
    .Where(cs => cs.Seller.Id == id) 
    .SelectMany(cs => cs.Customer.Payments); 
var paymentList = qry.ToList(); 

如果Seller和Customer在CustomerSellers有複合唯一約束產生的Payment S的關係有沒有重複。否則，您需要在SelectMany後附加Distinct()。