连接表中的 EF Code First 附加列用于排序

Question

我有两个具有关系的实体，我为其创建了一个连接表

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"));
}

我想添加一个额外的列以允许按时间顺序排列 StudentImages。

我应该在哪里添加插入相关代码？

Answer 1

您想在您的应用程序中使用该新列吗？在这种情况下，您不能对您的模型执行此操作。多对多关系仅在联结表不包含主表外键以外的任何内容时才有效。一旦添加了向应用程序公开的附加列，联结表就会像任何其他实体一样成为实体 = 您需要第三类。您的模型应如下所示：

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; }
}

而且你的映射也必须改变：

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); 
}