EF多实体对应单表

Posted 2021-02-16 bro-ma

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
    )

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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; }
    }

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 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[100];
            byte[] fullBits = new byte[2000];
            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();
        }

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