映射一
Mapping the Table-Per-Hierarchy (TPH) Inheritance
模型文件
using System.Data.Entity; using System.Data.Entity.ModelConfiguration.Conventions; namespace DataAnnotations { public class TestContext : DbContext { public DbSet<Course> Courses { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); modelBuilder.Entity<Course>() .Map<Course>(m => m.Requires("Type").HasValue("Course")) .Map<OnlineCourse>(m => m.Requires("Type").HasValue("OnlineCourse")); } }//class public class Course { public int CourseID { get; set; } public string Title { get; set; } public int Credits { get; set; } }//class public partial class OnlineCourse : Course { public string URL { get; set; } }//class }
对应的数据库代码：
CREATE TABLE [dbo].[Course] ( [CourseID] INT IDENTITY (1, 1) NOT NULL, [Title] NVARCHAR (MAX) NULL, [Credits] INT NOT NULL, [URL] NVARCHAR (MAX) NULL, [Type] NVARCHAR (128) NOT NULL, CONSTRAINT [PK_dbo.Course] PRIMARY KEY CLUSTERED ([CourseID] ASC) );
此是默认的策略，去掉建造者中的配置信息，代码如下：
using System.Data.Entity; using System.Data.Entity.ModelConfiguration.Conventions; namespace DataAnnotations { public class TestContext : DbContext { public DbSet<Course> Courses { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); } }//class public class Course { public int CourseID { get; set; } public string Title { get; set; } public int Credits { get; set; } }//class public partial class OnlineCourse : Course { public string URL { get; set; } }//class }
生成的数据库代码：
CREATE TABLE [dbo].[Course] ( [CourseID] INT IDENTITY (1, 1) NOT NULL, [Title] NVARCHAR (MAX) NULL, [Credits] INT NOT NULL, [URL] NVARCHAR (MAX) NULL, [Discriminator] NVARCHAR (128) NOT NULL, CONSTRAINT [PK_dbo.Course] PRIMARY KEY CLUSTERED ([CourseID] ASC) );
可见，鉴别器列被命名为Discriminator，其保存记录的类名称。
映射二
Mapping the Table-Per-Type (TPT) Inheritance
模型文件：
using System.Data.Entity; using System.Data.Entity.ModelConfiguration.Conventions; namespace DataAnnotations { public class TestContext : DbContext { public DbSet<Course> Courses { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); //TPT modelBuilder.Entity<Course>().ToTable("Course"); modelBuilder.Entity<OnlineCourse>().ToTable("OnlineCourse"); } } public class Course { public int CourseID { get; set; } public string Title { get; set; } public int Credits { get; set; } } public partial class OnlineCourse : Course { public string URL { get; set; } } }
将类型名称与表名称对应，生成的数据库代码：
CREATE TABLE [dbo].[Course] ( [CourseID] INT IDENTITY (1, 1) NOT NULL, [Title] NVARCHAR (MAX) NULL, [Credits] INT NOT NULL, CONSTRAINT [PK_dbo.Course] PRIMARY KEY CLUSTERED ([CourseID] ASC) ); ------------------------------------------------------------------------------------------ CREATE TABLE [dbo].[OnlineCourse] ( [CourseID] INT NOT NULL, [URL] NVARCHAR (MAX) NULL, CONSTRAINT [PK_dbo.OnlineCourse] PRIMARY KEY CLUSTERED ([CourseID] ASC), CONSTRAINT [FK_dbo.OnlineCourse_dbo.Course_CourseID] FOREIGN KEY ([CourseID]) REFERENCES [dbo].[Course] ([CourseID]) ); GO CREATE NONCLUSTERED INDEX [IX_CourseID] ON [dbo].[OnlineCourse]([CourseID] ASC);
派生类对应的表会有一个外键，将派生表的主键与基类对应的主表关联，形成0/1..1的关系。
映射三
Mapping the Table-Per-Concrete Class (TPC) Inheritance
模型：
using System.ComponentModel.DataAnnotations; using System.ComponentModel.DataAnnotations.Schema; using System.Data.Entity; using System.Data.Entity.ModelConfiguration.Conventions; namespace DataAnnotations { public class TestContext : DbContext { public DbSet<Course> Courses { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); //TPC modelBuilder.Entity<OnlineCourse>().Map(m => { m.MapInheritedProperties(); m.ToTable("OnlineCourse"); }); } } public class Course { [Key] [DatabaseGenerated(DatabaseGeneratedOption.None)] public int CourseID { get; set; } public string Title { get; set; } public int Credits { get; set; } } public partial class OnlineCourse : Course { public string URL { get; set; } } }
生成的数据库代码：
CREATE TABLE [dbo].[Course] ( [CourseID] INT NOT NULL, [Title] NVARCHAR (MAX) NULL, [Credits] INT NOT NULL, CONSTRAINT [PK_dbo.Course] PRIMARY KEY CLUSTERED ([CourseID] ASC) ); ----------------------------------------------------------------------------------------- CREATE TABLE [dbo].[OnlineCourse] ( [CourseID] INT NOT NULL, [Title] NVARCHAR (MAX) NULL, [Credits] INT NOT NULL, [URL] NVARCHAR (MAX) NULL, CONSTRAINT [PK_dbo.OnlineCourse] PRIMARY KEY CLUSTERED ([CourseID] ASC) );
注意，主键在整个继承层次结构上唯一，而不是单个表上唯一。
映射四
Mapping Properties of an Entity Type to Multiple Tables in the Database (Entity Splitting)
模型：
using System; using System.Data.Entity; namespace DataAnnotations { public class TestContext : DbContext { public DbSet<Department> Departments { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<Department>() .Map(m => { m.Properties(t => new { t.DepartmentID, t.Name }); m.ToTable("Department"); }) .Map(m => { m.Properties(t => new { t.DepartmentID, t.StartDate }); m.ToTable("DepartmentDetails"); }); } } public class Department { public int DepartmentID { get; set; } public string Name { get; set; } public DateTime StartDate { get; set; } } }
生成的数据库代码：
CREATE TABLE [dbo].[Department] ( [DepartmentID] INT IDENTITY (1, 1) NOT NULL, [Name] NVARCHAR (MAX) NULL, CONSTRAINT [PK_dbo.Department] PRIMARY KEY CLUSTERED ([DepartmentID] ASC) ); ---------------------------------------------------------------------------------------- CREATE TABLE [dbo].[DepartmentDetails] ( [DepartmentID] INT NOT NULL, [StartDate] DATETIME NOT NULL, CONSTRAINT [PK_dbo.DepartmentDetails] PRIMARY KEY CLUSTERED ([DepartmentID] ASC), CONSTRAINT [FK_dbo.DepartmentDetails_dbo.Department_DepartmentID] FOREIGN KEY ([DepartmentID]) REFERENCES [dbo].[Department] ([DepartmentID]) ); GO CREATE NONCLUSTERED INDEX [IX_DepartmentID] ON [dbo].[DepartmentDetails]([DepartmentID] ASC);
每个表都包含主键，第一个表的主键Identity，第二个表的主键无Identity，外键将两个表的主键关联。
映射五
Mapping Multiple Entity Types to One Table in the Database (Table Splitting)
这个模式主要用于懒惰加载，模型文件：
using System.ComponentModel.DataAnnotations; using System.Data.Entity; namespace DataAnnotations { public class TestContext : DbContext { public DbSet<Instructor> Instructors { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<Instructor>() .HasRequired(t => t.OfficeAssignment) .WithRequiredPrincipal(t => t.Instructor); modelBuilder.Entity<Instructor>().ToTable("Instructor"); modelBuilder.Entity<OfficeAssignment>().ToTable("Instructor"); } }// TestContext public class Instructor { public int InstructorID { get; set; } public string Name { get; set; } // 导航属性 public OfficeAssignment OfficeAssignment { get; set; } } public class OfficeAssignment { [Key] public int InstructorID { get; set; } public string Location { get; set; } // 导航属性 public Instructor Instructor { get; set; } } }
生成的数据库代码为：
CREATE TABLE [dbo].[Instructor] ( [InstructorID] INT IDENTITY (1, 1) NOT NULL, [Name] NVARCHAR (MAX) NULL, [Location] NVARCHAR (MAX) NULL, CONSTRAINT [PK_dbo.Instructor] PRIMARY KEY CLUSTERED ([InstructorID] ASC) );
