实体框架代码优先关系和导航属性? [英] Entity Framework code first relationships and navigation property?

问题描述

我有以下课程

public class Subject{
        public int SubjectId { get; set; }
        public String SubjectName { get; set; }
        public String SubjectCategory { get; set; }
    }

public class QuestionDescriptor {
        public int QuestionDescriptorId { get; set; }        
        public String QuestionText { get; set; }
        public String Answer { get; set; } 
        public int SubjectId { get; set; }
        public virtual Subject Subject { get; set; }
    }

我已使用以下代码对其进行了配置，我希望一个Subject可以具有许多QuestionDescriptor

i have configured it using the following code ,i want that a Subject can have many QuestionDescriptors

 modelBuilder.Entity<QuestionDescriptor>()
                .HasRequired(qd => qd.Subject)
                .WithMany()
                .HasForeignKey(qd => qd.SubjectId)
                .WillCascadeOnDelete(true);

现在我有以下问题

1. 我做对了吗?
2. 我在Subject类中需要导航属性吗?

3. 如果我这样做会发生什么

1. have i done it correctly ?
2. do i need a navigation property in the Subject class?

3. what happems if i do this

public class Subject {
        public int SubjectId { get; set; }
        public String SubjectName { get; set; }
        public String SubjectCategory { get; set; }
        public int QuestionDescriptorId {get;set;}
        public virtual QuestionDescriptor {get;set;} 
    }

如果执行上述操作，我需要在配置中进行哪些更改以及为什么?

if i do the above what changes do i need in the configuration and why?

推荐答案

1)我做对了吗?

1) have i done it correctly ?

是的

2)我在Subject类中需要导航属性吗?

2) do i need a navigation property in the Subject class?

不.不用了对于某些查询可能有所帮助，但这不是必需的.

No. You don't need it. It can be helpful for certain queries but it is not required.

3)如果我这样做会发生什么...

3) what happems if i do this ...

那是另一种关系.这将代表一对一的关系.但是，由于您想要一对多关系，因此您的实体上必须具有导航 collection :

That's another relationship. It would represent a one-to-one relationship. But because you want a one-to-many relationship you must have a navigation collection on your entity:

public class Subject {
    public int SubjectId { get; set; }
    public String SubjectName { get; set; }
    public String SubjectCategory { get; set; }
    public virtual ICollection<QuestionDescriptor> Descriptors {get;set;} 
}

4)如果执行上述操作，我需要在配置中进行哪些更改， 为什么?

4) if i do the above what changes do i need in the configuration and why?

对于上述更改，您可以保持映射配置不变-唯一的例外是，您现在必须将集合指定为关系的另一侧.代替.WithMany()而是使用

For the change above you can leave you mapping configuration as it is - with the only exception that you now must specify the collection as the other side of the relationship. Instead of .WithMany() you use

.WithMany(s => s.Descriptors)

5)如果我想要属于某个特定主题的所有问题，那么 我可以通过查询QuestionDescriptor来获取它们，为什么我需要 双向属性?

5) if i want all the questions belonging to a particular subject then i can get them by querying the QuestionDescriptor ,why then do i need a bi-directional property ?

您不需要它.

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