Entity Framework 6.x 学习之 - 创建带连接表的实体模型 with Database First
一、Modeling a Many-to-Many Relationship with No Payload
1. 创建数据库表
CREATE TABLE [Album] ( [AlbumId] [int] NOT NULL IDENTITY(1, 1), [AlbumName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ) ON [PRIMARY] GO ALTER TABLE [Album] ADD CONSTRAINT [PK_Album] PRIMARY KEY CLUSTERED ([AlbumId]) ON [PRIMARY] GO CREATE TABLE [Artist] ( [ArtistId] [int] NOT NULL IDENTITY(1, 1), [FirstName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL, [MiddleName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL, [LastName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ) ON [PRIMARY] GO ALTER TABLE [Artist] ADD CONSTRAINT [PK_Artist] PRIMARY KEY CLUSTERED ([ArtistId]) ON [PRIMARY] GO CREATE TABLE [LinkTable] ( [ArtistId] [int] NOT NULL, [AlbumId] [int] NOT NULL ) ON [PRIMARY] GO ALTER TABLE [LinkTable] ADD CONSTRAINT [PK_LinkTable] PRIMARY KEY CLUSTERED ([ArtistId], [AlbumId]) ON [PRIMARY] GO ALTER TABLE [LinkTable] ADD CONSTRAINT [FK_LinkTable_Album] FOREIGN KEY ([AlbumId]) REFERENCES [Album] ([AlbumId]) GO ALTER TABLE [LinkTable] ADD CONSTRAINT [FK_LinkTable_Artist] FOREIGN KEY ([ArtistId]) REFERENCES [Artist] ([ArtistId]) GO
表关系图：
2. 创建实体模型，如图
备注：明明选了3个表，为什么只有2个实体呢？
因为中间那个表为连接表，所以在映射实体的时候只有2个实体，这种情况叫 no payload 。
为什么连接表不会被创建成一个实体呢？
因为他没有自己的字段，如果给链接表加一个字段，那么创建的实体模型就会和数据库表关系一样，一个一个的对应上。
3. 操作实体类
1 using System; 2 3 namespace ConsoleApplication3 4 { 5 class Program 6 { 7 static void Main(string[] args) 8 { 9 //Insert 10 using (var context = new test2Entities()) 11 { 12 //添加一个艺术家属于2个专辑 13 var artist = new Artist { FirstName = "Alan", LastName = "Jackson" }; 14 var album1 = new Album { AlbumName = "Drive" }; 15 var album2 = new Album { AlbumName = "Live at Texas Stadium" }; 16 artist.Albums.Add(album1); 17 artist.Albums.Add(album2); 18 context.Artists.Add(artist); 19 20 //添加一个专辑有2个艺术家 21 var artist1 = new Artist { FirstName = "Tobby", LastName = "Keith" }; 22 var artist2 = new Artist { FirstName = "Merle", LastName = "Haggard" }; 23 var album = new Album { AlbumName = "Honkytonk University" }; 24 artist1.Albums.Add(album); 25 artist2.Albums.Add(album); 26 context.Albums.Add(album); 27 28 context.SaveChanges(); 29 } 30 31 //Select 32 using (var context = new test2Entities()) 33 { 34 Console.WriteLine("艺术家和他们的专辑..."); 35 var artists = context.Artists; 36 foreach (var artist in artists) 37 { 38 Console.WriteLine("{0} {1}", artist.FirstName, artist.LastName); 39 foreach (var album in artist.Albums) 40 { 41 Console.WriteLine("\t{0}", album.AlbumName); 42 } 43 } 44 45 Console.WriteLine("\n专辑中的艺术家..."); 46 var albums = context.Albums; 47 foreach (var album in albums) 48 { 49 Console.WriteLine("{0}", album.AlbumName); 50 foreach (var artist in album.Artists) 51 { 52 Console.WriteLine("\t{0} {1}", artist.FirstName, artist.LastName); 53 } 54 } 55 } 56 Console.ReadKey(); 57 } 58 } 59 }
输出：
程序运行3次后的数据库表结果：
二、Modeling a Many-to-Many Relationship with a Payload
1. 创建数据库表：
CREATE TABLE [Order] ( [OrderId] [int] NOT NULL, [OrderDate] [datetime] NOT NULL ) ON [PRIMARY] GO ALTER TABLE [Order] ADD CONSTRAINT [PK_Order] PRIMARY KEY CLUSTERED ([OrderId]) ON [PRIMARY] GO CREATE TABLE [Item] ( [SKU] [int] NOT NULL, [Description] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL, [Price] [decimal] (18, 2) NOT NULL ) ON [PRIMARY] GO ALTER TABLE [Item] ADD CONSTRAINT [PK_Item] PRIMARY KEY CLUSTERED ([SKU]) ON [PRIMARY] GO CREATE TABLE [OrderItem] ( [OrderId] [int] NOT NULL, [SKU] [int] NOT NULL, [Count] [int] NOT NULL ) ON [PRIMARY] GO ALTER TABLE [OrderItem] ADD CONSTRAINT [PK_OrderItem] PRIMARY KEY CLUSTERED ([OrderId], [SKU]) ON [PRIMARY] GO ALTER TABLE [OrderItem] ADD CONSTRAINT [FK_OrderItem_Item] FOREIGN KEY ([SKU]) REFERENCES [Item] ([SKU]) GO ALTER TABLE [OrderItem] ADD CONSTRAINT [FK_OrderItem_Order] FOREIGN KEY ([OrderId]) REFERENCES [Order] ([OrderId]) GO
表关系图：
创建模型图：
这回连接表有了实体了，为什么呢？因为OrderItem表有自己的字段Count
3. 操作实体类：
using System; namespace ConsoleApplication4 { class Program { static void Main(string[] args) { //Add using (var context = new test2Entities()) { var order = new Order { OrderId = 100, OrderDate = new DateTime(2010, 1, 18) }; var item = new Item { SKU = 11729, Description = "Backpack", Price = 29.97M }; var oi = new OrderItem { Order = order, Item = item, Count = 1 }; context.Items.Add(item); context.OrderItems.Add(oi); item = new Item { SKU = 12929, Description = "Water Filter", Price = 13.97M }; oi = new OrderItem { Order = order, Item = item, Count = 3 }; context.Items.Add(item); context.OrderItems.Add(oi); item = new Item { SKU = 11847, Description = "Camp Stove", Price = 43.99M }; oi = new OrderItem { Order = order, Item = item, Count = 1 }; context.Items.Add(item); context.OrderItems.Add(oi); context.Orders.Add(order); context.SaveChanges(); } //Select using (var context = new test2Entities()) { foreach (var order in context.Orders) { Console.WriteLine("Order # {0}, ordered on {1}", order.OrderId.ToString(), order.OrderDate.ToShortDateString()); Console.WriteLine("SKU\tDescription\tQty\tPrice"); Console.WriteLine("---\t-----------\t---\t-----"); foreach (var oi in order.OrderItems) { Console.WriteLine("{0}\t{1}\t{2}\t{3}", oi.Item.SKU, oi.Item.Description, oi.Count.ToString(), oi.Item.Price.ToString("C")); } } } Console.ReadKey(); } } }