标签：inf name with lin efi ipa [] get field
1.1 拆分实体到多张表
假设你有如下表，如图6-1。Product表用于存储商品的字符类信息，ProductWebInfo用于存储商品的图片，两张表通过SKU关联。现在你想把两张表的信息整合到一个实体类。
图6-1
1.2 使用code first 新建如下的poco实体：
public class Product { [Key] [DatabaseGenerated(DatabaseGeneratedOption.None)] public int SKU { get; set; } public string Description { get; set; } public decimal Price { get; set; } public string ImageURL { get; set; } }
1.3 创建一个继承自DbContext的数据访问类“EF6RecipesContext”
public class EF6RecipesContext : DbContext { public DbSet<Product> Products { get; set; } public EF6RecipesContext() : base("name=EF6CodeFirstRecipesContext") { } protected override void OnModelCreating(DbModelBuilder modelBuilder) { base.OnModelCreating(modelBuilder); modelBuilder.Entity<Product>() .Map(m => { m.Properties(p => new { p.SKU, p.Description, p.Price }); m.ToTable("Product"); }) .Map(m => { m.Properties(p => new { p.SKU, p.ImageURL }); m.ToTable("ProductWebInfo"); }); } }
1.4 测试代码：
1 using (var context = new EF6RecipesContext()) 2 { 3 var product = new Product 4 { 5 SKU = 147, 6 Description = "Expandable Hydration Pack", 7 Price = 19.97M, 8 ImageURL = "/pack147.jpg" 9 }; 10 context.Products.Add(product); 11 product = new Product 12 { 13 SKU = 178, 14 Description = "Rugged Ranger Duffel Bag", 15 Price = 39.97M, 16 ImageURL = "/pack178.jpg" 17 }; 18 context.Products.Add(product); 19 product = new Product 20 { 21 SKU = 186, 22 Description = "Range Field Pack", 23 Price = 98.97M, 24 ImageURL = "/noimage.jp" 25 }; 26 context.Products.Add(product); 27 product = new Product 28 { 29 SKU = 202, 30 Description = "Small Deployment Back Pack", 31 Price = 29.97M, 32 ImageURL = "/pack202.jpg" 33 }; 34 context.Products.Add(product); 35 context.SaveChanges(); 36 } 37 using (var context = new EF6RecipesContext()) 38 { 39 foreach (var p in context.Products) 40 { 41 Console.WriteLine("{0} {1} {2} {3}", p.SKU, p.Description, 42 p.Price.ToString("C"), p.ImageURL); 43 } 44 }
2.1 分拆一张表到多个实体
你有这样的一张数据库表如图6-2，里面包含经常使用的字符，一些不常用的大字段。为了性能，需要避免每个查询都去加载这些字段。你需要将这张表分拆成两个或是更多的实体。
图6-2
2.2 把上面的表分拆成两个poco实体。
1 public class Photograph 2 { 3 [Key] 4 [DatabaseGenerated(DatabaseGeneratedOption.Identity)] 5 public int PhotoId { get; set; } 6 public string Title { get; set; } 7 public byte[] ThumbnailBits { get; set; } 8 [ForeignKey("PhotoId")] 9 public virtual PhotographFullImage PhotographFullImage { get; set; } 10 } 11 12 public class PhotographFullImage 13 { 14 [Key] 15 public int PhotoId { get; set; } 16 public byte[] HighResolutionBits { get; set; } 17 [ForeignKey("PhotoId")] 18 public virtual Photograph Photograph { get; set; } 19 }
2.3 创建ef数据访问类，并注册表拆分规则。
1 public class EF6RecipesContext2:DbContext 2 { 3 public EF6RecipesContext2() 4 : base("name=EF6CodeFirstRecipesContext") 5 { 6 } 7 public DbSet<Photograph> Photographs { get; set; } 8 public DbSet<PhotographFullImage> PhotographFullImages { get; set; } 9 protected override void OnModelCreating(DbModelBuilder modelBuilder) 10 { 11 base.OnModelCreating(modelBuilder); 12 13 modelBuilder.Entity<Photograph>() 14 .HasRequired(p => p.PhotographFullImage) 15 .WithRequiredPrincipal(p => p.Photograph); 16 17 modelBuilder.Entity<Photograph>().ToTable("Photograph"); 18 modelBuilder.Entity<PhotographFullImage>().ToTable("Photograph"); 19 } 20 }
2.4 测试代码：
1 byte[] thumbBits = new byte[100]; 2 byte[] fullBits = new byte[2000]; 3 using (var context = new EF6RecipesContext2()) 4 { 5 var photo = new Photograph 6 { 7 Title = "My Dog", 8 ThumbnailBits = thumbBits 9 }; 10 var fullImage = new PhotographFullImage { HighResolutionBits = fullBits }; 11 photo.PhotographFullImage = fullImage; 12 context.Photographs.Add(photo); 13 context.SaveChanges(); 14 } 15 using (var context = new EF6RecipesContext2()) 16 { 17 //context.Configuration.LazyLoadingEnabled = false;//1 如果关闭演示加载，则注释2必须写上 18 foreach (var photo in context.Photographs) 19 { 20 Console.WriteLine("Photo: {0}, ThumbnailSize {1} bytes", 21 photo.Title, photo.ThumbnailBits.Length); 22 23 //显式加载存储完整图像的字段 24 //context.Entry(photo).Reference(p => p.PhotographFullImage).Load();//2 这里指定显示加载 25 Console.WriteLine("Full Image Size: {0} bytes", 26 photo.PhotographFullImage.HighResolutionBits.Length); 27 } 28 }
输出如下：
Photo: My Dog, Thumbnail Size: 100 bytes
Full Image Size: 2000 bytes
2.5 ef的默认规则是开发延迟加载的，所以在我们获取“Photograph”的时候，其对应的“PhotographFullImage”是不会加载进来的，只有使用到“PhotographFullImage”的属性的时候才会加载进来。
entityframework学习笔记--006-表拆分与实体拆分
标签：inf name with lin efi ipa [] get field
原文地址：http://www.cnblogs.com/renjing/p/6134944.html
