如何实现实体框架代码首先加入 [英] How to implement Entity Framework Code First join

问题描述

我开始使用实体框架代码。

假设有这样的POCO（最终简化）：

  public BortStructure类
 {
 public Guid Id {get;组; } 
 public String Name {get;组; 
} 
 
 public class Slot 
 {
 public Guid Id {get;组; } 
 public String Name {get;组; } 
 public BortStructure {get;组; } 
} 
 
 public class SystemType 
 {
 public Guid Id {get;组; } 
 public String Name {get;组; } 
} 
 
 public class SlotSystemType 
 {
 public Guid Id {get;组; } 
 public Slot Slot {get;组; } 
 public SystemType SystemType {get;组; 
} 
  

和上下文

  public MyContext：DbContext 
 {
 public DbSet< BortStructure> BortStructures {get;组; } 
 public DbSet< Slot>老虎机{get;组; } 
 public DbSet< SystemType> SystemTypes {get;组; } 
 public DbSet< SlotSystemType> SlotSystemTypes {get;组; 
} 
  

我有一个任务可以通过Id列出附带的插槽来获取BortStructure，每个都附有systemTypes列表。

使用SQL可以让我用一些JOIN来实现：

  SELECT BortStructures.Id，BortStructures.Name，Slots.Id，
 Slots.Name，SystemType.Id，SystemType.Name FROM 
（（BortStructures LEFT JOIN Slots ON BortStructures。 Id = Slots.BortStructureId）
 LEFT JOIN SlotSystemTypes ON SlotSystemTypes.SlotId = Slots.Id）
 LEFT JOIN SystemTypes ON SystemTypes.Id = SlotSystemTypes.SystemTypeId 
 WHERE BortStructures.Id ='XXXXXX'ORDER BY Slots.Id，SystemType.Id 
  

但是实体框架代码首先我没有任何想法如何使用

如果我使用

  var slotSystemTypes = from sl在MyContext.SlotSystemTypes 
其中sl.Slot.BortStructure.Id = XXXXXX 
 orderby sl.Slot.Id，sl.SystemType.Id 
 select sl; 
  

当然，如果BortStructure由没有附加任何SystemTypes的Slots / Slots组成，我将不会收到任何内容。

而不是使用空插槽/插槽的空列表获得BortStructure，每个都附有我希望获得的SystemTypes的空列表。

有没有办法使用单一 LINQ查询来存档我的数据库配置？

解决方案

您可以使用 join 运算符示例：

  string [] category = new string [] {
饮料，
调味品，
蔬菜，
乳制品，
海鲜} ; 
 
列表<产品> products = GetProductList（）; 
 
 var q = 
从c在类别
中连接p在c上的产品等于p.Category 
 select new {Category = c，p.ProductName}; 
 
 foreach（var v in q）
 {
 Console.WriteLine（v.ProductName +：+ v.Category）; 
} 
  

更多示例： http://code.msdn.microsoft.com/LINQ-Join-Operators-dabef4e9

I'm starting to use Entity Framework Code First.

Suppose to have such POCO's (ultimately simplified):

public class BortStructure
{
   public Guid Id { get; set; }
   public String Name { get; set; }
}

public class Slot
{
   public Guid Id { get; set; }
   public String Name { get; set; }
   public BortStructure { get; set; }
}

public class SystemType
{
   public Guid Id { get; set; }
   public String Name {get; set; }
}

public class SlotSystemType
{
   public Guid Id { get; set; }
   public Slot Slot { get; set; }
   public SystemType SystemType {get; set; }
}

and a context

public MyContext : DbContext
{
   public DbSet<BortStructure> BortStructures { get; set; }
   public DbSet<Slot> Slots{ get; set; }
   public DbSet<SystemType> SystemTypes { get; set; }
   public DbSet<SlotSystemType> SlotSystemTypes { get; set; }
}

I have a task to get BortStructure by Id with list of attached Slots, each one with list of systemTypes attached.

Using SQL allowed me to do that with some JOIN's:

SELECT BortStructures.Id, BortStructures.Name, Slots.Id, 
Slots.Name, SystemType.Id, SystemType.Name FROM
((BortStructures LEFT JOIN Slots ON BortStructures.Id = Slots.BortStructureId)
LEFT JOIN SlotSystemTypes ON SlotSystemTypes.SlotId = Slots.Id)
LEFT JOIN SystemTypes ON SystemTypes.Id = SlotSystemTypes.SystemTypeId
WHERE BortStructures.Id='XXXXXX' ORDER BY Slots.Id, SystemType.Id

But with Entity Framework Code First I don't have any idea howto do that.

If I use

var slotSystemTypes = from sl in MyContext.SlotSystemTypes
where sl.Slot.BortStructure.Id = XXXXXX
orderby sl.Slot.Id, sl.SystemType.Id
select sl;

i, of course, will receive nothing if BortStructure consists of no Slots/Slots without any SystemTypes attached.

Instead of getting BortStructure with empty list of Slots/with Slots, each one with empty list of SystemTypes attached as I expect to get.

Is there any way to archive that with single LINQ query for my database configuration?

解决方案

You can use join operator example:

string[] categories = new string[]{  
    "Beverages",   
    "Condiments",   
    "Vegetables",   
    "Dairy Products",   
    "Seafood" };  

List<Product> products = GetProductList(); 

var q = 
    from c in categories 
    join p in products on c equals p.Category 
    select new { Category = c, p.ProductName }; 

foreach (var v in q) 
{ 
    Console.WriteLine(v.ProductName + ": " + v.Category);  
} 

more samples in: http://code.msdn.microsoft.com/LINQ-Join-Operators-dabef4e9

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