Entity Framework 4.1 之四：復雜類型
原文名稱：Entity Framework 4.1: Complex Types (4)
原文地址：http://vincentlauzon.wordpress.com/2011/04/13/entity-framework-4-1-complex-types-4/
看到 Entity Framework 4.1 推薦英文教程，為了幫大家看起來方便一些，簡單翻譯一下。這是一個系列，共有 8 篇，這是第 4 篇。
默認情況下，EF4.1 將類映射到表，這是約定，但是有時候，我們需要模型比表的粒度更細一些。
地址是一個典型的例子，看一下下面的客戶類。
publicclass Client
{
publicint ClientID { get; set; }
[Required]
[StringLength(32, MinimumLength=2)]
publicstring ClientName { get; set; }
public Address ResidentialAddress { get; set; }
public Address DeliveryAddress { get; set; }
}
publicclass Address
{
[Required]
publicint StreetNumber { get; set; }
[Required]
[StringLength(32, MinimumLength=2)]
publicstring StreetName { get; set; }
}
{
publicint ClientID { get; set; }
[Required]
[StringLength(32, MinimumLength=2)]
publicstring ClientName { get; set; }
public Address ResidentialAddress { get; set; }
public Address DeliveryAddress { get; set; }
}
publicclass Address
{
[Required]
publicint StreetNumber { get; set; }
[Required]
[StringLength(32, MinimumLength=2)]
publicstring StreetName { get; set; }
}
我們不希望其中的兩個地址屬性都映射到地址表中的記錄，而是讓 EF4.1 都映射到一張表中，將地址展開，如何做到呢？可以通過復雜類型。
像我們前面看到的，我們總是通過標簽或者模型構建器來覆蓋默認約定。我提到過，當我們豐富業務模型的時候，例如必填項，我建議使用屬性。現在我考慮將類中的復雜屬性映射到表中的字段，所以這里不是用標簽，而是使用模型構建器。
protectedoverridevoid OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Client>().Property(x => x.ClientID)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
modelBuilder.ComplexType<Address>();
modelBuilder.Entity<Client>().Property(i => i.ResidentialAddress.StreetNumber).HasColumnName("ResStreetNumber");
modelBuilder.Entity<Client>().Property(i => i.ResidentialAddress.StreetName).HasColumnName("ResStreetName");
modelBuilder.Entity<Client>().Property(i => i.DeliveryAddress.StreetNumber).HasColumnName("DelStreetNumber");
modelBuilder.Entity<Client>().Property(i => i.DeliveryAddress.StreetName).HasColumnName("DelStreetName");
}
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Client>().Property(x => x.ClientID)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
modelBuilder.ComplexType<Address>();
modelBuilder.Entity<Client>().Property(i => i.ResidentialAddress.StreetNumber).HasColumnName("ResStreetNumber");
modelBuilder.Entity<Client>().Property(i => i.ResidentialAddress.StreetName).HasColumnName("ResStreetName");
modelBuilder.Entity<Client>().Property(i => i.DeliveryAddress.StreetNumber).HasColumnName("DelStreetNumber");
modelBuilder.Entity<Client>().Property(i => i.DeliveryAddress.StreetName).HasColumnName("DelStreetName");
}
首先，我指定 client-id 作為自動增長的標識列。然后，指定 Address 是復雜類型。如果愿意的話，也可以將 [ComplexType] 標簽加到類上來說明。然后，使用 Lambda 表達式將每一個子屬性映射到列上，這將會生成如下的表。
現在，可以使用模型了。
using (var context1 =new MyDomainContext())
{
var client =new Client
{
ClientName ="Joe",
ResidentialAddress =new Address
{
StreetNumber =15,
StreetName ="Oxford"
},
DeliveryAddress =new Address
{
StreetNumber =514,
StreetName ="Nolif"
}
};
context1.Clients.Add(client);
context1.SaveChanges();
}
using (var context2 =new MyDomainContext())
{
var clients = from w in context2.Clients
where w.ClientName =="Joe"
select w;
foreach (var client in clients)
{
Console.WriteLine("client residential StreetNumber: "+ client.ResidentialAddress.StreetNumber);
Console.WriteLine("client residential StreetName: "+ client.ResidentialAddress.StreetName);
Console.WriteLine("client delivery StreetNumber: "+ client.DeliveryAddress.StreetNumber);
Console.WriteLine("client delivery StreetName: "+ client.DeliveryAddress.StreetName);
}
}
{
var client =new Client
{
ClientName ="Joe",
ResidentialAddress =new Address
{
StreetNumber =15,
StreetName ="Oxford"
},
DeliveryAddress =new Address
{
StreetNumber =514,
StreetName ="Nolif"
}
};
context1.Clients.Add(client);
context1.SaveChanges();
}
using (var context2 =new MyDomainContext())
{
var clients = from w in context2.Clients
where w.ClientName =="Joe"
select w;
foreach (var client in clients)
{
Console.WriteLine("client residential StreetNumber: "+ client.ResidentialAddress.StreetNumber);
Console.WriteLine("client residential StreetName: "+ client.ResidentialAddress.StreetName);
Console.WriteLine("client delivery StreetNumber: "+ client.DeliveryAddress.StreetNumber);
Console.WriteLine("client delivery StreetName: "+ client.DeliveryAddress.StreetName);
}
}
對于復雜類型，最值得注意的是空的管理。即使復雜類型的所有屬性都是可空的，你也不能將整個復雜類型的對象設為 null, 例如，在這種情況下，即使街道的名稱和街道的號碼不是必填的，也不能有一個住宅的地址為 null，需要創建一個所有屬性都是 null 的地址對象來表示。同樣的道理，當你獲取一個實體的時候，即使所有的屬性都是 null ，EF4.1 也將會創建一個復雜類型的對象。
浙公網安備 33010602011771號