EF多实体对应单表

1、EF多实体对应单表

适用场景：单数据库表，表数据有较长用字段，有不常用或者大数据字段。

2、建表语句　　

CREATE TABLE [Chapter2].[Photograph](
    [PhotoId] [int] IDENTITY(1,1) primary key NOT NULL,
    [Title] [varchar](50) NOT NULL,
    [ThumbnailBits] [image] NOT NULL,
    [HighResolutionBits] [image] NOT NULL
    )

3、新建控制程序，添加EntityFramework 引用。

4、创建两个实体实体，实体由同一个表不同字段组成。

public class PictureContext : DbContext
    {
        public DbSet<Photograph> Photographs { get; set; }
        public DbSet<PhotographFullImage> PhotographFullImage { get; set; }
 
        public PictureContext() : base("EFRecipesEntities")
        {
 
        }
 
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
 
            modelBuilder.Entity<Photograph>()
                .HasRequired(p => p.PhotographFullImage)
                .WithRequiredPrincipal(p => p.Photograph);
 
            modelBuilder.Entity<Photograph>().ToTable("Photograph", "Chapter2");
            modelBuilder.Entity<PhotographFullImage>().ToTable("Photograph", "Chapter2");
        }
    }
 
    public class Photograph
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int PhotoId { get; set; }
        public string Title { get; set; }
        public byte[] ThumbnailBits { get; set; }
        [ForeignKey("PhotoId")]
        public virtual PhotographFullImage PhotographFullImage { get; set; }
    }
 
    public class PhotographFullImage
    {
        [Key]
        public int PhotoId { get; set; }
        public byte[] HighResolutionBits { get; set; }
        [ForeignKey("PhotoId")]
        public virtual Photograph Photograph { get; set; }
    }

注意图中指定Photograph实体需要(HasRequired) PhotographFullImage实体，并通过WithRequiredPrincipal,指定主键由Photograph负责。

5、修改Main程序如下：

　　

 static void Main(string[] args)
        {
            byte[] thumbBits = new byte[];
            byte[] fullBits = new byte[];
            using (var context = new PictureContext())
            {
                var photo = new Photograph
                {
                    Title = "My Dog",
                    ThumbnailBits = thumbBits
                };
                var fullImage = new PhotographFullImage { HighResolutionBits = fullBits };
                photo.PhotographFullImage = fullImage;
                context.Photographs.Add(photo);
                context.SaveChanges();
            }
            using (var context = new PictureContext())
            {
                foreach (var photo in context.Photographs)
                {
                    Console.WriteLine("Photo: {0}, ThumbnailSize {1} bytes",
                        photo.Title, photo.ThumbnailBits.Length);
                    // explicitly load the "expensive" entity,
                    context.Entry(photo).Reference(p => p.PhotographFullImage).Load();
                    Console.WriteLine("Full Image Size: {0} bytes",
                        photo.PhotographFullImage.HighResolutionBits.Length);
                }
            }
 
            Console.ReadKey();
        }