Types of Entity in Entity Framework

最新推荐文章于 2021-05-17 17:23:37 发布

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最新推荐文章于 2021-05-17 17:23:37 发布

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分类专栏： Entity Framework 文章标签： entity framework

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本文介绍了Entity Framework 5.0/6.0中的两种实体类型：POCO实体和动态代理实体。POCO实体是不依赖任何特殊框架基类的普通CLR对象，而动态代理实体是POCO的运行时代理，支持懒加载和自动更改跟踪。要作为POCO代理，实体需要满足特定条件，如非密封、非抽象等。实体的属性分为标量属性（对应数据库列）和导航属性（指向相关实体）。

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在Entity Framwork 5.0/6.0中有两种类型实体:POCO 实体和动态代理实体

POCO(Plain Old CLR Object) 实体:

POCO类是不依赖任何框架中特殊的基类，它与其它普通的.net类类似所以才叫"Plain Old CLR Objects".
这些POCO类支持大部分的查询，插入，修改，删除那些通过Entity Data Model生成的实体操作。

  public class Student
        {
            public Student()
            {
                this.Courses = new List<Course>();
            }
    
            public int StudentID { get; set; }
            public string StudentName { get; set; }
            public Nullable<int> StandardId { get; set; }
    
            public Standard Standard { get; set; }
            public StudentAddress StudentAddress { get; set; }
            public IList<Course> Courses { get; set; }
        }

Dynamic Proxy:

Dynamic Proxy是一个POCO 实体在运行时的代理类，它可看作是POCO实体的包装类。
动态代理实体可以Lazy loading和automatic change tracking.
POCO 实体应该符合下面要求才可用作POCO proxy:
1.一个POCO 类必须被声明为public.
2.一个POCO 类必须不能是sealed.
3.一个POCO 类必须不能是abstract.
4.每个导航属性必须声明为public,virtual.
5.每个collection属性必须是ICollect<T>.
6.ProxyCreationEnabled option 必须是true(默认是true)在context类.

以下是Student POCO实体都符合上述的要求在运行时会看成Dynamic proxy entity.

 public class Student
 {
            public Student()
            {
                this.Courses = new HashSet<Course>();
            }
    
            public int StudentID { get; set; }
            public string StudentName { get; set; }
            public Nullable<int> StandardId { get; set; }
    
            public virtual Standard Standard { get; set; }
            public virtual StudentAddress StudentAddress { get; set; }
            public virtual ICollection<Course> Courses { get; set; }
 }

Entity can have two types of properties, Scalar properties and Navigation properties.

Scalar properties:

Scalar properties are properties whose actual values are contained in the entity. For example, Student entity has scalar properties e.g. StudentId, StudentName. These correspond with the Student table columns.

Navigation properties:

Navigation properties are pointers to other related entities. The Student has Standard property as a navigation property that will enable application to navigate from a Student to related Standard entity.