与EF codeFirst和SqlCe4唯一约束

问题描述

我在写使用实体框架code首先和SqlCe4的ASP.net应用MVC3

I'm writing an ASP.net MVC3 application using Entity Framework Code First and SqlCe4.

我一直在设计几款车型，发现一个正在变成很有趣。这是我到目前为止有：

I have been designing several models, and found one that is turning out to be interesting. This is what I have so far:

public class Preference
    {
        public int PreferenceId { get; set; }

        [Required]
        public int StudentId { get; set; }
        public virtual Student Student { get; set; }

        [Required]
        public int PresentationId { get; set; }
        public virtual Presentation Presentation { get; set; }

        [Required]
        public int Rank { get; set; }
    }

我然而，需要一个唯一的约束或索引，因为对于一个特定的学生，我希望他们要有preferences的列表，但presentationId需要为每个学生独特。有没有办法通过code首先还是一些验证属性来做到这一点？

I however, need a unique constraint or index, because for a particular student, I want them to have to have a list of preferences, but the PresentationId needs to be unique for each student. Is there a way to do this via Code First or some validation attribute?

这听起来像我要下了许多的分支与preference对象是中介一对多的关系，要添加等级属性。不过，我似乎无法找到如何确保该值是唯一的。是最好的方式真的手动只是EF之外增加一个唯一索引数据库？

This sounds like I'm going down the branch of a many to many relationship with the Preference object being an intermediary, to add the Rank property. However, I can't seem to find how to make sure that the values are unique. Is the best way really to manually just add a unique index to the database outside of EF?

推荐答案

去什么Eranga说的话，我最终使它同样的工作，但像这样的：

Going with what Eranga was saying, I ended up making it work similarly, but like this:

我用下面的code在我的DataContext类：

I used the following code in my DataContext class:

public class StudentRegistrationContext : DbContext
{
    public StudentRegistrationContext()
    {
        Database.SetInitializer(new StudentRegistrationDatabaseInitializer());
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Teacher> Teachers { get; set; }
    public DbSet<Presenter> Presenters { get; set; }
    public DbSet<Presentation> Presentations { get; set; }
}

在数据库初始化器类，我用了以下内容：

In the Database Initializer class, I used the following:

public class StudentRegistrationDatabaseInitializer : DropCreateDatabaseIfModelChanges<StudentRegistrationContext>
{
    protected override void Seed(StudentRegistrationContext context)
    {
        base.Seed(context);
        context.Database.ExecuteSqlCommand("CREATE UNIQUE INDEX UX_Preferences_StudentId_PresentationId ON Preferences (StudentId, PresentationId)");
    }
}

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