联接表中的EF Code First附加列用于订购 [英] EF Code First Additional column in join table for ordering purposes

问题描述

我有两个具有关联关系的实体，我为此创建了一个联接表

I have two entities that have a relationship for which I create a join table

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }

    public virtual ICollection<Image> Images { get; set; }
}


public class Image
{
    public int Id { get; set; }
    public string Filename { get; set; }

    public virtual ICollection<Student> Students { get; set; }
}


protected override void OnModelCreating(DbModelBuilder modelBuilder)
{

        modelBuilder.Entity<Student>()
            .HasMany(i => i.Images)
            .WithMany(s => s.Students)
            .Map(m => m.ToTable("StudentImages"));
}

我想增加一列以按时间顺序排列StudentImages.

I would like to add an additional column to allow chronological ordering of the StudentImages.

我应该在哪里添加相关代码?

Where should I add insert the relevant code?

推荐答案

是否要在应用程序中使用该新列?在这种情况下，您将无法使用模型执行此操作.多对多关系仅在联结表除主表的外键之外不包含其他任何内容的情况下才起作用.一旦向应用程序添加了其他列，联结表便成为实体，就像其他任何实体一样=您需要第三类.您的模型应如下所示:

Do you want to use that new column in your application? In such case you cannot do that with your model. Many-to-many relation works only if junction table doesn't contain anything else than foreign keys to main tables. Once you add additional column exposed to your application, the junction table becomes entity as any other = you need third class. Your model should look like:

public class StudentImage 
{
    public int StudentId { get; set; }
    public int ImageId { get; set; }
    public int Order { get; set; }
    public virtual Student Student { get; set; }
    public virtual Image Image { get; set; }
}

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<StudentImage> Images { get; set; }
}


public class Image
{
    public int Id { get; set; }
    public string Filename { get; set; }
    public virtual ICollection<StudentImage> Students { get; set; }
}

您的映射也必须更改:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<StudentImages>().HasKey(si => new { si.StudentId, si.ImageId });

    // The rest should not be needed - it should be done by conventions
    modelBuilder.Entity<Student>()
                .HasMany(s => s.Images)
                .WithRequired(si => si.Student)
                .HasForeignKey(si => si.StudentId); 
    modelBuilder.Entity<Image>()
                .HasMany(s => s.Students)
                .WithRequired(si => si.Image)
                .HasForeignKey(si => si.ImageId); 
}

这篇关于联接表中的EF Code First附加列用于订购的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！