NHibernate - 關係

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在本章中，我們將瞭解 NHibernate 中的關係。讓我們將注意力轉向如何理解 NHibernate 中的關係。最簡單的方法是從資料庫的角度來思考這些關係。

• 我們首先建立一個新的應用程式，在其中我們將建立客戶和訂單實體之間的一些關係。

• 我們將要研究的第一個關係是經典的集合關係。

• 我們有一個客戶，以及一個訂單集合。

• 這是一個一對多關係，它在資料庫中由 2 個表表示，訂單表上有一個客戶 ID，並且我們有一個指向客戶的反向外部索引鍵關係。

首先，我們需要建立一個數據庫和兩個表 Customer 和 Order。您可以在 SQL Server 資源管理器中指定以下查詢來建立它們。

USE [master] 
GO 
CREATE DATABASE [NHibernateDemo] 
GO 
USE [NHibernateDemo] 
GO

CREATE TABLE [dbo].[Customer]( 
   [Id] [uniqueidentifier] NOT NULL, 
   [FirstName] [nvarchar](100) NOT NULL, 
   [LastName] [nvarchar](100) NOT NULL, 
   [Points] [int] NULL, [HasGoldStatus] [bit] NULL, 
   [MemberSince] [date] NULL, 
   [CreditRating] [nchar](20) NULL, 
   [AverageRating] [decimal](18, 4) NULL, 
   [Street] [nvarchar](100) NULL, 
   [City] [nvarchar](100) NULL, 
   [Province] [nvarchar](100) NULL, 
   [Country] [nvarchar](100) NULL,
   PRIMARY KEY CLUSTERED ([Id] ASC) 
) 

GO 
CREATE TABLE [dbo].[Order]( 
   [Id] [uniqueidentifier] NOT NULL, 
   [CustomerId] [uniqueidentifier] NULL, 
   [Ordered] [datetime] NULL, 
   [Shipped] [datetime] NULL, 
   [Street] [nvarchar](100) NULL, 
   [City] [nvarchar](100) NULL, 
   [Province] [nvarchar](100) NULL, 
   [Country] [nvarchar](100) NULL, 
   PRIMARY KEY CLUSTERED ([Id] ASC) 
) 
GO

它將在資料庫中建立兩個表。下圖顯示了 Customer 表。

下圖顯示了 Order 表，您可以在其中看到指向客戶的反向外部索引鍵關係。

我們需要在app.config 檔案中定義連線字串，以下是 app.config 檔案的實現。

<?xml version = "1.0" encoding = "utf-8" ?> 
<configuration> 
   
   <connectionStrings> 
      <add name = "default" connectionString = "Data Source =
         (localdb)\MSSQLLocalDB;Initial Catalog = NHibernateDemo;Integrated Security =
         True;Connect Timeout = 30;Encrypt = False;TrustServerCertificate = False;
         ApplicationIntent = ReadWrite;MultiSubnetFailover = False"/> 
   </connectionStrings> 

</configuration>

要在您的應用程式中安裝 NHibernate，請在 NuGet Manager 控制檯視窗中執行以下命令。

install-package NHibernate

要配置 NHibernate 配置，我們需要在hibernate.cfg.xml 檔案中定義配置，如下面的程式碼所示。

<xml version = "1.0" encoding = "utf-8" ?> 
<hibernate-configuration xmlns = "urn:nhibernate-configuration-2.2"> 
   
   <session-factory> 
      <property name = "connection.connection_string_name">default</property>
		
      <property name = "connection.driver_class">
         NHibernate.Driver.SqlClientDriver 
      </property> 
		
      <property name = "dialect">
         NHibernate.Dialect.MsSql2008Dialect
      </property> 
		
      <property name = "show_sql">true</property> 
   </session-factory> 

</hibernate-configuration>

在這個例子中，我們將使用兩個領域類，Customer 和 Order。

以下是 Customer.cs 檔案的實現，其中我們有兩個類，一個是 Customer 類，另一個是 Location 類，其中物件用作 Customer 類中的地址。

using System; 
using System.Text; 
using Iesi.Collections.Generic;

namespace NHibernateDemo {
 
   public class Customer { 
      
      public Customer() { 
         MemberSince = DateTime.UtcNow; 
         Orders = new HashedSet<Order>(); 
      } 
      
      public virtual Guid Id { get; set; } 
      public virtual string FirstName { get; set; } 
      public virtual string LastName { get; set; } 
      public virtual double AverageRating { get; set; } 
      public virtual int Points { get; set; } 
		
      public virtual bool HasGoldStatus { get; set; }
      public virtual DateTime MemberSince { get; set; } 
      public virtual CustomerCreditRating CreditRating { get; set; } 
      public virtual Location Address { get; set; }
		
      public virtual ISet<Order> Orders { get; set; }
      public virtual void AddOrder(Order order) { Orders.Add(order); order.Customer = this; }
      
      public override string ToString() { 
         var result = new StringBuilder();
			
         result.AppendFormat("{1} {2} ({0})\r\n\tPoints: {3}\r\n\tHasGoldStatus:
            {4}\r\n\tMemberSince: {5} ({7})\r\n\tCreditRating: {6}\r\n\tAverageRating:
            {8}\r\n", Id, FirstName, LastName, Points, HasGoldStatus, MemberSince,
            CreditRating, MemberSince.Kind, AverageRating);
            result.AppendLine("\tOrders:"); 
         
         foreach(var order in Orders) { 
            result.AppendLine("\t\t" + order); 
         } 
			
         return result.ToString(); 
      } 
   }
   
   public class Location { 
      public virtual string Street { get; set; } 
      public virtual string City { get; set; } 
      public virtual string Province { get; set; } 
      public virtual string Country { get; set; } 
   }
   
   public enum CustomerCreditRating { 
      Excellent,
      VeryVeryGood, 
      VeryGood, 
      Good, 
      Neutral, 
      Poor, 
      Terrible 
   } 
}

以下是對映檔案Customer.hbm.xml，其中 Customer 類對映到 Customer 表。

<?xml version = "1.0" encoding = "utf-8" ?> 
<hibernate-mapping xmlns = "urn:nhibernate-mapping-2.2" assembly = "NHibernateDemo" 
   namespace = "NHibernateDemo"> 
	
   <class name = "Customer"> 
   
      <id name = "Id"> 
         <generator class = "guid.comb"/> 
      </id> 

      <property name = "FirstName"/> 
      <property name = "LastName"/> 
      <property name = "AverageRating"/> 
      <property name = "Points"/> 
      <property name = "HasGoldStatus"/> 
      <property name = "MemberSince" type = "UtcDateTime"/> 
      <property name = "CreditRating" type = "CustomerCreditRatingType"/>
      
      <component name = "Address"> 
         <property name = "Street"/> 
         <property name = "City"/> 
         <property name = "Province"/> 
         <property name = "Country"/> 
      </component> 

   </class> 
</hibernate-mapping>

我們還有一個 Order 類，以下是Order.cs 檔案的實現。

using System; using Iesi.Collections.Generic;

namespace NHibernateDemo { 

   public class Order { 
      
      public virtual Guid Id { get; set; } 
      public virtual DateTime Ordered { get; set; } 
      public virtual DateTime? Shipped { get; set; }
      public virtual Location ShipTo { get; set; } 
      public virtual Customer Customer { get; set; }
      
      public override string ToString() { 
         return string.Format("Order Id: {0}", Id); 
      } 
   } 
}

多對一關係

我們還需要將 Order 類對映到資料庫中的 Order 表，所以以下是Order.hbm.xml 檔案的實現。

<?xml version = "1.0" encoding = "utf-8" ?> 
<hibernate-mapping xmlns = "urn:nhibernate-mapping-2.2" assembly = "NHibernateDemo" 
   namespace = "NHibernateDemo"> 

   <class name = "Order" table = "`Order`"> 
   
      <id name = "Id"> 
         <generator class = "guid.comb"/> 
      </id> 
		
      <property name = "Ordered"/> 
      <property name = "Shipped"/> 
   
      <component name = "ShipTo"> 
         <property name = "Street"/> 
         <property name = "City"/> 
         <property name = "Province"/> 
         <property name = "Country"/> 
      </component> 

      <!--<many-to-one name = "Customer" column = "CustomerId" cascade =
         "save-update"/>--> 
			
   </class> 
</hibernate-mapping>

一對多關係

在這裡，我們將看一下一對多關係，在本例中，客戶和訂單之間。我們在這裡有我們的客戶，我們正在建立一個新的客戶，您可以看到該集合已初始化為以下訂單對。

private static Customer CreateCustomer() { 
   
   var customer = new Customer { 
      FirstName = "John", 
      LastName = "Doe", 
      Points = 100, 
      HasGoldStatus = true, 
      MemberSince = new DateTime(2012, 1, 1), 
      CreditRating = CustomerCreditRating.Good, 
      AverageRating = 42.42424242, 
      Address = CreateLocation() 
   }; 
   
   var order1 = new Order { 
      Ordered = DateTime.Now 
   }; 
   
   customer.AddOrder(order1); 
   var order2 = new Order { 
      Ordered = DateTime.Now.AddDays(-1), 
      Shipped = DateTime.Now, 
      ShipTo = CreateLocation() 
   }; 
   
   customer.AddOrder(order2); 
   return customer; 
}

因此，我們將建立一個新的客戶並儲存它，儲存後，我們將找到 ID 並在 Main 方法中的另一個會話中重新載入它，如下面的程式所示。

private static void Main() { 

   var cfg = ConfigureNHibernate(); 
   var sessionFactory = cfg.BuildSessionFactory();
   
   Guid id; 
   using(var session = sessionFactory.OpenSession()) 
	
   using(var tx = session.BeginTransaction()) { 
      var newCustomer = CreateCustomer(); 
      Console.WriteLine("New Customer:"); 
      Console.WriteLine(newCustomer);
      session.Save(newCustomer); 
      id = newCustomer.Id; 
      tx.Commit(); 
   }
   
   using(var session = sessionFactory.OpenSession()) 
	
   using(var tx = session.BeginTransaction()) { 
      var reloaded = session.Load<Customer>(id); 
      Console.WriteLine("Reloaded:"); 
      Console.WriteLine(reloaded); 
      tx.Commit(); 
   }
   
   Console.WriteLine("Press <ENTER> to exit..."); 
   Console.ReadLine(); 
}

以下是完整的Program.cs 檔案實現。

using System; 
using System.Data; 
using System.Linq; 
using System.Reflection; 

using HibernatingRhinos.Profiler.Appender.NHibernate; 
using NHibernate.Cfg; 
using NHibernate.Dialect; 
using NHibernate.Driver; 
using NHibernate.Linq;

namespace NHibernateDemo {
 
   internal class Program { 
	
      private static void Main() { 
		
         var cfg = ConfigureNHibernate(); 
         var sessionFactory = cfg.BuildSessionFactory();
         
         Guid id; 
         using(var session = sessionFactory.OpenSession())
			
         using(var tx = session.BeginTransaction()) { 
            var newCustomer = CreateCustomer(); 
            Console.WriteLine("New Customer:"); 
            Console.WriteLine(newCustomer); 
            session.Save(newCustomer); 
            id = newCustomer.Id; 
            tx.Commit(); 
         } 
         
         using(var session = sessionFactory.OpenSession()) 
			
         using(var tx = session.BeginTransaction()) { 
            var reloaded = session.Load<Customer>(id); 
            Console.WriteLine("Reloaded:"); 
            Console.WriteLine(reloaded); 
            tx.Commit();
         }
         
         Console.WriteLine("Press <ENTER> to exit..."); 
         Console.ReadLine();
      }
      
      private static Customer CreateCustomer() { 
		
         var customer = new Customer { 
            FirstName = "John", 
            LastName = "Doe", 
            Points = 100, 
            HasGoldStatus = true, 
            MemberSince = new DateTime(2012, 1, 1), 
            CreditRating = CustomerCreditRating.Good, 
            AverageRating = 42.42424242, 
            Address = CreateLocation() 
         }; 
         
         var order1 = new Order { 
            Ordered = DateTime.Now
         }; 
         
         customer.AddOrder(order1); 
			
         var order2 = new Order { 
            Ordered = DateTime.Now.AddDays(-1), 
            Shipped = DateTime.Now, 
            ShipTo = CreateLocation() 
         }; 
         
         customer.AddOrder(order2); 
         return customer; 
      } 
      
      private static Location CreateLocation() { 
		
         return new Location { 
            Street = "123 Somewhere Avenue", 
            City = "Nowhere", 
            Province = "Alberta", 
            Country = "Canada" 
         }; 
      } 
      
      private static Configuration ConfigureNHibernate() { 
         NHibernateProfiler.Initialize(); 
         var cfg = new Configuration(); 
         
         cfg.DataBaseIntegration(x =&ht; { 
            x.ConnectionStringName = "default"; 
            x.Driver<SqlClientDriver>(); 
            x.Dialect<MsSql2008Dialect>(); 
            x.IsolationLevel = IsolationLevel.RepeatableRead; 
            x.Timeout = 10; x.BatchSize = 10; 
         }); 
         
         cfg.SessionFactory().GenerateStatistics();
         cfg.AddAssembly(Assembly.GetExecutingAssembly()); 
         return cfg; 
      } 
   } 
}

當您執行此應用程式時，您將看到以下輸出。

New Customer:

John Doe (00000000-0000-0000-0000-000000000000)
   Points: 100
   HasGoldStatus: True
   MemberSince: 1/1/2012 12:00:00 AM (Unspecified)
   CreditRating: Good
   AverageRating: 42.42424242

   Orders:
      Order Id: 00000000-0000-0000-0000-000000000000
      Order Id: 00000000-0000-0000-0000-000000000000

Reloaded:
John Doe (9b0fcf10-83f6-4f39-bda5-a5b800ede2ba)
   Points: 100
   HasGoldStatus: True
   MemberSince: 1/1/2012 12:00:00 AM (Utc)
   CreditRating: Good
   AverageRating: 42.4242

   Orders:
Press <ENTER> to exit...

正如您所看到的，最初客戶有 2 個訂單，但是當我們重新載入它時，沒有看到任何訂單。如果您檢視customer.hbm.xml 檔案，您可以在此處看到我們沒有對映實際的 orders 集合。因此，NHibernate 對此一無所知。讓我們繼續新增它。

<?xml version = "1.0" encoding = "utf-8" ?> 
<hibernate-mapping xmlns = "urn:nhibernate-mapping-2.2" 
   assembly = "NHibernateDemo" namespace = "NHibernateDemo">
	
   <class name = "Customer"> 
      
      <id name = "Id">
         <generator class = "guid.comb"/> 
      </id> 
      
      <property name = "FirstName"/>
      <property name = "LastName"/> 
      <property name = "AverageRating"/> 
      <property name = "Points"/> 
      <property name = "HasGoldStatus"/> 
      <property name = "MemberSince" type = "UtcDateTime"/> 
      <property name = "CreditRating" type = "CustomerCreditRatingType"/>
      
      <component name = "Address"> 
         <property name = "Street"/> 
         <property name = "City"/> 
         <property name = "Province"/> 
         <property name = "Country"/> 
      </component>
      
      <set name = "Orders" table = "`Order`"> 
         <key column = "CustomerId"/> 
         <one-to-many class = "Order"/> 
      </set> 
   
   </class> 
</hibernate-mapping>

這是一個集合，這個集合的名稱是“Orders”，它儲存在一個名為 order 的表中。我們需要指定一個鍵，即外部索引鍵的名稱或查詢訂單。這些訂單透過客戶 ID 被識別或屬於某個客戶。然後我必須注意這是一個一對多關係，它與 Order 類有關。

我們還需要稍微更改 Main 方法，以便將新的客戶訂單也儲存到資料庫中，如下面的程式所示。

private static void Main() { 

   var cfg = ConfigureNHibernate(); 
   var sessionFactory = cfg.BuildSessionFactory();
   
   Guid id; 
   using(var session = sessionFactory.OpenSession()) 
	
   using(var tx = session.BeginTransaction()) {
      var newCustomer = CreateCustomer(); 
      Console.WriteLine("New Customer:"); 
      Console.WriteLine(newCustomer);
      session.Save(newCustomer); 
      
      foreach (var order in newCustomer.Orders) { 
         session.Save(order); 
      } 
		
      id = newCustomer.Id; 
      tx.Commit(); 
   }
   
   using(var session = sessionFactory.OpenSession()) 
	
   using(var tx = session.BeginTransaction()) { 
      var reloaded = session.Load<Customer>(id); 
      Console.WriteLine("The orders were ordered by: "); 
      
      foreach (var order in reloaded.Orders) { 
         Console.WriteLine(order.Customer); 
      } 
		
      tx.Commit(); 
   }
   Console.WriteLine("Press <ENTER> to exit..."); Console.ReadLine();
}

我們還指定了哪個客戶訂購了該特定產品。因此，我們需要建立一個多對一關係，以將該訂單關聯回該客戶。

所以讓我們進入Order.hbm.xml 檔案並新增一個多對一，然後命名客戶欄位和帶有客戶 ID 的列。

<?xml version = "1.0" encoding = "utf-8" ?> 
<hibernate-mapping xmlns = "urn:nhibernate-mapping-2.2" assembly = "NHibernateDemo"
   namespace = "NHibernateDemo"> 
	
   <class name = "Order" table = "`Order`">
      
      <id name = "Id"> 
         <generator class = "guid.comb"/> 
      </id>
      
      <property name = "Ordered"/> 
      <property name = "Shipped"/> 
      
      <component name = "ShipTo"> 
         <property name = "Street"/> 
         <property name = "City"/> 
         <property name = "Province"/> 
         <property name = "Country"/> 
      </component> 

      <many-to-one name = "Customer" column = "CustomerId"/> 
		
   </class> 
</hibernate-mapping>

讓我們再次執行此應用程式，現在您將看到以下輸出。

New Customer:
John Doe (00000000-0000-0000-0000-000000000000)
   Points: 100
   HasGoldStatus: True
   MemberSince: 1/1/2012 12:00:00 AM (Unspecified)
   CreditRating: Good
   AverageRating: 42.42424242

   Orders:
      Order Id: 00000000-0000-0000-0000-000000000000
      Order Id: 00000000-0000-0000-0000-000000000000

Reloaded:
John Doe (660a6f29-650e-4380-99e0-a5b800febbde)
   Points: 100
   HasGoldStatus: True
   MemberSince: 1/1/2012 12:00:00 AM (Utc)
   CreditRating: Good
   AverageRating: 42.4242

   Orders:
      Order Id: 57314deb-e023-4e55-ac1e-a5b800febbe3
      Order Id: fc065683-d5f5-484b-ae42-a5b800febbe3

The orders were ordered by:
John Doe (660a6f29-650e-4380-99e0-a5b800febbde)
   Points: 100
   HasGoldStatus: True
   MemberSince: 1/1/2012 12:00:00 AM (Utc)
   CreditRating: Good
   AverageRating: 42.4242

   Orders:
      Order Id: 57314deb-e023-4e55-ac1e-a5b800febbe3
      Order Id: fc065683-d5f5-484b-ae42-a5b800febbe3

John Doe (660a6f29-650e-4380-99e0-a5b800febbde)
   Points: 100
   HasGoldStatus: True
   MemberSince: 1/1/2012 12:00:00 AM (Utc)
   CreditRating: Good
   AverageRating: 42.4242

   Orders:
      Order Id: 57314deb-e023-4e55-ac1e-a5b800febbe3
      Order Id: fc065683-d5f5-484b-ae42-a5b800febbe3
		
Press <ENTER> to exit...