什么是实体框架中的复杂类型以及何时使用它？

I have tried to read the msdn article on complex types. But it does not explain when to use it. Also there is not a comprehensive explanation on the web on complex types and when to use them.

我试图阅读有关复杂类型的msdn文章。但它没有解释何时使用它。此外，在网络上没有关于复杂类型以及何时使用它们的全面解释。

2 个解决方案

#1

The lengthy explanation is in the MSDN article you linked... so you basically want an easy explanation:

冗长的解释是在你链接的MSDN文章中...所以你基本上想要一个简单的解释：

A complex type is a set of properties that exist in its own object for C#, but are mapped to columns on an already existing table (the one for the entity that contains it), instead of having its own table (which would need a key, etc.).

复杂类型是一组属性，它们存在于C＃自己的对象中，但是映射到现有表（包含它的实体的表）上的列，而不是拥有自己的表（需要一个键）等）。

So imagine you want this table on the database:

所以想象一下你想在数据库上使用这个表：

Orders
----------
Id (bigint)
Name (varchar)
Street (varchar)
Region (varchar)
Country (varchar)

But want this structure in the C# entities:

但是想在C＃实体中使用这个结构：

class Order
{
   long Id;
   string Name;

   struct Address
   {
     string Street;
     string Region;
     string Country;
   }
}

So there Address would be a complex type: it would not exist on its own (there wouldn't be Addresses table) on the database... it would only exist as a set of columns on the Orders table.

因此，Address将是一个复杂的类型：它不会自己存在（在数据库上没有Addresses表）...它只会作为Orders表上的一组列存在。

As noted by @HenkHolterman in the comments, the value of having complex types is having a single C# entity which can be used as a value for other containing entities (in my example, you could have an Address in a Supplier entity, for example, but it will just be mapped as a set of columns in the Suppliers table). It makes it easy to work with the values in the complex type.

正如@HenkHolterman在评论中所指出的，具有复杂类型的价值是拥有一个C＃实体，可以将其用作其他包含实体的值（在我的示例中，您可以在供应商实体中拥有一个地址，例如，但它只会被映射为Suppliers表中的一组列。它使得处理复杂类型中的值变得容易。

The disadvantage is precisely that one: you may have to repeat the complex type values many times in the database if it happens that a same Address (or whatever other type you use) can be shared among different entities.

缺点恰恰在于：如果碰巧在不同实体之间共享相同的地址（或您使用的任何其他类型），则可能必须在数据库中多次重复复杂类型值。

Whether you choose to work with complex types or separate entities is up to you and your design.

无论您选择使用复杂类型还是单独的实体，都取决于您和您的设计。

#2

Consider this ContactDetails class for example:

考虑这个ContactDetails类，例如：

public class ContactDetails
{
    public string HomePhone { get; set; }
    public string MobilePhone { get; set; }
    public string FaxNumber { get; set; }
}

By default, EF will treat ContactDetails as an Entity. That means that if (for example) you're having a Person class with a navigation-property of ContactDetails type, EF will map the Person.ContactDetails relationship to a different table (because Entity is something that is having an identity of its own, hence other entities may refer to it - and that would require a different table in relational terms).

默认情况下，EF会将ContactDetails视为实体。这意味着如果（例如）你有一个带有ContactDetails类型的导航属性的Person类，EF会将Person.ContactDetails关系映射到另一个表（因为Entity是具有自己身份的东西，因此，其他实体可能会引用它 - 这需要在关系术语中使用不同的表格。

By denoting ContactDetails as a Complex Type instead, EF will no longer treat it as an entity that requires a relationship and instead map it to the same table of the parent (containing) entity (Person in my example), effectively making it a Value Object.

通过将ContactDetails表示为复杂类型，EF将不再将其视为需要关系的实体，而是将其映射到父（包含）实体（我的示例中为Person）的同一个表中，从而有效地使其成为值对象。

#1