代码优先数据注释 - 如何引用非外键的对象 [英] Code-first data annotations - how to reference objects that are not foreign keys

问题描述

我来自LINQ2SQL。我有一个对象"人物"它具有对象"地址"的引用。

I'm coming from the LINQ2SQL. I have an object "Person" that has a reference to object "Address".

下面的代码将生成两个表 - 一个带有fk到地址表的Person表。

The code below will generate two tables - a Person table with a fk to the Address table.

// LINQ2SQL
[Association(ThisKey = "AddressId", ... etc
Public EntityRef<Address> HomeAddress = new EntityRef<Address>();
// EF4
[ForeignKey("AddressId")]
public Address HomeAddress {...}

现在，使用LINQ2SQL，我也可以使用对Address对象的简单引用，这将生成一个表 - 一个Person表，其地址字段被非规范化为Person表。

Now, with LINQ2SQL, I can also use a plain reference to the Address object, and this will generate a single table - a Person table with the address fields denormalized into the Person table.

// LINQ2SQL
public Address HomeAddress() ...
// EF4 equivalent
// HELP? what do I put here?

我可以在EF4中这样做？我使用哪些数据注释？

Can I do this in EF4? What data annotations do I use?

感谢您的帮助，

Ray

Thank you for your help,
Ray

 

推荐答案

对于您希望拥有结构化数据的方案放到实体所在的表中，您将使用复杂类型。使用CodeFirst，基本上有三种方法可以实现这一目标。


1）您可能只想确保依赖类型（在您的情况下为地址）不会被识别为EntityType。通常删除以Id结尾的字段应该可以解决问题。

2）您可以使用[ComplexType]属性装饰依赖类型（在您的情况下为Address），以告知该类型不应该是被视为实体

3）您可以在DbContext.OnModelCreating方法中配置一个类型作为复杂类型（您需要从DbContext派生并覆盖OnModelCreating方法），如下所示：

For the scenarios when you would like to have structured data put to the table where the entity lives you would use complex types. With CodeFirst there are basically three ways of achieving this.
1) You may just want to make sure that the dependent type (in your case Address) will not be recognized as an EntityType. Usually removing the field that ends with Id should do the trick.
2) You may just decorate the dependent type (in you case Address) with the [ComplexType] attribute to tell that the type should not be treated as Entity
3) You may configure a type as a complex type in DbContext.OnModelCreating method (you need to derive from DbContext and override the OnModelCreating method) like this:

modelBuilder.ComplexType<Address>();

您不需要在您的实体中执行任何特殊操作。以下是完整的示例：

You don't need to do anything special in your entity. Here is the full example:

重要的是要记住复杂的属性

One thing that is important to remember that complex property

  public class CustomersDB : DbContext 
  {
    public DbSet<Customer> Customers { get; set; }
  }

  public class Customer
  {
    public int ID { get; set; }
    public string Name { get; set; }
    public Address HomeAddress { get; set; }
  }

  public class Address
  {
    public string Street { get; set; }
    public string City { get; set; }
  }

  public static void Main()
  {
    using (var ctx = new CustomersDB())
    {
      ctx.Customers.Add(new Customer()
      {
        ID = 1,
        Name = "Test",
        HomeAddress = new Address()
        {
          Street = "1st NE",
          City = "Seattle"
        }
      });

      ctx.SaveChanges();
    }
  } 

值得一提的有关复杂属性的一件事是复杂属性不能为空。如果complex属性的所有子属性都为null，但复杂属性本身不能为null，则完美无缺。否则，当您尝试将实体保存到数据库时，您将获得
异常。

One thing about complex properties that is worth mentioning is that complex properties must not be null. It is perfectly if all the child properties of the complex property are null but the complex property itself must not be null. Otherwise you will get an exception when trying to save the entity to the database.

Pawel

 

 

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