Entity Framework。解决零或一对一使用一个导航属性

Question

对不起我的英语。我有以下实体：

public class MediaAlbum
{
    [Key]
    public Guid AlbumId { get; set; }

    public string Title { get; set; }

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

    public Guid? CoverId { get; set; }
    [ForeignKey("ImageId")]
    public virtual MediaImage Cover { get; set; }
}

public class MediaImage
{
    [Key]
    public Guid ImageId { get; set; }

    public string Image { get; set; }

    public Guid AlbumId { get; set; }
    [ForeignKey("AlbumId")]
    public virtual MediaAlbum Album { get; set; }
}

我需要地图导航属性覆盖到实体 'MediaImage'。我试图通过fluentApi解决，但没有成功：

   modelBuilder.Entity<MediaAlbum>().HasOptional(x => x.Cover).WithOptionalPrincipal()
            .Map(x => x.MapKey("ImageId"));

Answer 1

试试这个：

modelBuilder.Entity<MediaAlbum>()
         .HasOptional(x => x.Cover)
         .WithRequired(x => x.Album)
         .WillCascadeOnDelete();

Answer 2

使用这个：

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<MediaAlbum>().HasMany(x => x.Images)
                    .WithRequired(x => x.Album).HasForeignKey(x=>x.AlbumId);
        modelBuilder.Entity<MediaAlbum>().HasOptional(x => x.Cover);
    }

外键是 CoverId 而不是 ImageId:

public class MediaAlbum
{
    [Key]
    public Guid AlbumId { get; set; }

    public string Title { get; set; }

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

    public Guid? CoverId { get; set; }
    [ForeignKey("CoverId")]// change to this
    public virtual MediaImage Cover { get; set; }
}

Entity Framework。解决零或一对一使用一个导航属性

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