Entity Framework Code First （四）Fluent API

　　上篇博文说过当我们定义的类不能遵循约定（Conventions）的时候，Code First 提供了两种方式来配置你的类：DataAnnotations 和 Fluent API, 本文将关注 Fluent API.

　　一般来说我们访问 Fluent API 是通过重写继承自 DbContext 的类中方法 OnModelCreating. 为了便于例示，我们先创建一个继承自 DbContext 的类，以及其它的一些类以便使用

public class SchoolEntities : DbContext

    {

        public DbSet<Course> Courses { get; set; }

        public DbSet<Department> Departments { get; set; }

        public DbSet<Instructor> Instructors { get; set; }

        public DbSet<OfficeAssignment> OfficeAssignments { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)

        {

            // Configure Code First to ignore PluralizingTableName convention

            // If you keep this convention then the generated tables will have pluralized names.

            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();

        }

    }

    public class Department

    {

        public Department()

        {

            this.Courses = new HashSet<Course>();

        }

        // Primary key

        public int DepartmentID { get; set; }

        public string Name { get; set; }

        public decimal Budget { get; set; }

        public System.DateTime StartDate { get; set; }

        public int? Administrator { get; set; }

        // Navigation property

        public virtual ICollection<Course> Courses { get; private set; }

    }

    public class Course

    {

        public Course()

        {

            this.Instructors = new HashSet<Instructor>();

        }

        // Primary key

        public int CourseID { get; set; }

        public string Title { get; set; }

        public int Credits { get; set; }

        // Foreign key

        public int DepartmentID { get; set; }

        // Navigation properties

        public virtual Department Department { get; set; }

        public virtual ICollection<Instructor> Instructors { get; private set; }

    }

    public partial class OnlineCourse : Course

    {

        public string URL { get; set; }

    }

    public partial class OnsiteCourse : Course

    {

        public OnsiteCourse()

        {

            Details = new Details();

        }

        public Details Details { get; set; }

    }

    public class Details

    {

        public System.DateTime Time { get; set; }

        public string Location { get; set; }

        public string Days { get; set; }

    }

    public class Instructor

    {

        public Instructor()

        {

            this.Courses = new List<Course>();

        }

        // Primary key

        public int InstructorID { get; set; }

        public string LastName { get; set; }

        public string FirstName { get; set; }

        public System.DateTime HireDate { get; set; }

        // Navigation properties

        public virtual ICollection<Course> Courses { get; private set; }

    }

    public class OfficeAssignment

    {

        // Specifying InstructorID as a primary

        [Key()]

        public Int32 InstructorID { get; set; }

        public string Location { get; set; }

        // When the Entity Framework sees Timestamp attribute

        // it configures ConcurrencyCheck and DatabaseGeneratedPattern=Computed.

        [Timestamp]

        public Byte[] Timestamp { get; set; }

        // Navigation property

        public virtual Instructor Instructor { get; set; }

    }

Model-Wide Setting

HasDefaultSchema() - Default Schema（EF6 onwards）

　　从 EF6 开始可以使用 DbModelBuilder 中的方法 HasDefaultSchema 来指定所有的表/存储过程/视图等属于哪一个 database schema

modelBuilder.HasDefaultSchema("sales");

　　PS 1: 在 EF 之前的版本中默认的 schema 是被 hard-coded 成 "dbo", 唯一改变它的方式是使用 ToTable API

　　PS 2: 解释一下 database schema, 它就是对诸如表、视图、存储过程等的一种逻辑分组的方式（可以想象成对象的集合），你可以把一个 schema 赋予用户以便他能够访问所有经过授权的对象。Schemas 在数据库中可以被创建并被更新，用户也可以被授权访问它，一个 schema 可以被定义成任意用户拥有，并且 schema 的所有权是可以被转移的。我们可以看一下数据库中的 schema

Custom Conventions（EF6 onwards）

　　约定配置请参考文章 http://www.cnblogs.com/panchunting/p/entity-framework-code-first-custom-conventions.html

Property Mapping 属性映射

HasKey() - Primary Key

　　指定属性为主键

// Primary Key

modelBuilder.Entity<OfficeAssignment>()

            .HasKey(t => t.InstructorID);

　　也可以指定多个属性为联合主键

// Composite Primary Key

modelBuilder.Entity<Department>()

            .HasKey(t => new { t.DepartmentID, t.Name });

HasDatabaseGeneratedOption()

　　为数字型主键取消数据库生成

// Switching off Identity for Numeric Primary Keys

modelBuilder.Entity<Department>()

            .Property(t => t.DepartmentID)

            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

HasMaxLength() - Specifying the Length on a Property

　　指定属性长度

// Specifying the Maximum Length on a Property

modelBuilder.Entity<Department>()

            .Property(t => t.Name)

            .HasMaxLength();

IsRequired() - Configuring the Property to be Required

　　必填字段

// Configuring the Property to be Required

modelBuilder.Entity<Department>()

            .Property(t => t.Name)

            .IsRequired();

Ignore() - Specifying Not to Map a CLR Property to a Column in the Database

　　忽略

// Specifying Not to Map a CLR Property to a Column in the Database

modelBuilder.Entity<Department>()

            .Ignore(t => t.Budget);

HasColumnName() - Mapping a CLR Property to a Specific Column in the Database

　　指定列名

// Mapping a CLR Property to a Specific Column in the Database

modelBuilder.Entity<Department>()

            .Property(t => t.Name)

            .HasColumnName("DepartmentName");

MapKey - Renaming a Foreign Key That Is Not Defined in the Model

　　指定外键名

// Renaming a Foreign Key That Is Not Defined in the Model

modelBuilder.Entity<Course>()

            .HasRequired(c => c.Department)

            .WithMany(t => t.Courses)

            .Map(m => m.MapKey("ChangedDepartmentID"));

HasColumnType() - Configuring the Data Type of a Database Column

　　指定列类型

// Configuring the Data Type of a Database Column

modelBuilder.Entity<Department>()

            .Property(p => p.Name)

            .HasColumnType("varchar");

Configuring Properties on a Complex Type

　　在复杂类型（Complex Type）上有两种方式来配置 scalar properties

　　在 ComplexTypeConfiguration 上调用 Property

// Call Property on ComplexTypeConfiguration

modelBuilder.ComplexType<Details>()

            .Property(t => t.Location)

            .HasMaxLength();

　　也可以使用点标记法来访问复杂类型上的属性

 // Use the dot notation to access a property of a complex type

 modelBuilder.Entity<OnsiteCourse>()

             .Property(t => t.Details.Location)

             .HasMaxLength();

IsConcurrencyToken() - Configuring a Property to Be Used as an Optimistic Concurrency Token

　　设置乐观并发标记

// Configuring a Property to Be Used as an Optimistic Concurrency Token

modelBuilder.Entity<OfficeAssignment>()

            .Property(t => t.Timestamp)

            .IsConcurrencyToken();

IsRowVersion() - Configuring a Property to Be Used as an Optimistic Concurrency Token

　　设置乐观并发标记，效果同上

// Configuring a Property to Be Used as an Optimistic Concurrency Token

modelBuilder.Entity<OfficeAssignment>()

            .Property(t => t.Timestamp)

            .IsRowVersion();

Type Mapping类型映射

ComplexType() - Specifying That a Class Is a Complex Type

　　指定复杂类型

// Specifying That a Class Is a Complex Type

modelBuilder.ComplexType<Details>();

Ingore() - Specifying Not to Map a CLR Entity Type to a Table in the Database

　　忽略实体类型

// Specifying Not to Map a CLR Entity Type to a Table in the Database

modelBuilder.Ignore<OnlineCourse>();

ToTable() - Mapping an Entity Type to a Specific Table in the Database

　　映射表名

// Mapping an Entity Type to a Specific Table in the Database

modelBuilder.Entity<Department>()

            .ToTable("t_Department");

　　也可以同时指定 schema

// Mapping an Entity Type to a Specific Table in the Database

modelBuilder.Entity<Department>()

            .ToTable("t_ Department", "school");

Mapping the Table-Per-Hierarchy (TPH) Inheritance

　　映射 TPH

// Mapping the Table-Per-Hierarchy (TPH) Inheritance

modelBuilder.Entity<Course>()

            .Map<Course>(m => m.Requires("Type").HasValue("Course"))

            .Map<OnsiteCourse>(m => m.Requires("Type").HasValue("OnsiteCourse"));

Mapping the Table-Per-Type (TPT) Inheritance

　　映射 TPT

// Mapping the Table-Per-Type (TPT) Inheritance

modelBuilder.Entity<Course>().ToTable("Course");

modelBuilder.Entity<OnsiteCourse>().ToTable("OnsiteCourse");

Mapping the Table-Per-Concrete Class (TPC) Inheritance

　　映射 TPC

// Mapping the Table-Per-Concrete Class (TPC) Inheritance

modelBuilder.Entity<Course>()

            .Property(c => c.CourseID)

            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

modelBuilder.Entity<OnsiteCourse>()

            .Map(m =>

            {

                m.MapInheritedProperties();

                m.ToTable("OnsiteCourse");

            });

modelBuilder.Entity<OnlineCourse>()

            .Map(m =>

            {

                m.MapInheritedProperties();

                m.ToTable("OnlineCourse");

            });

Mapping Properties of an Entity Type to Multiple Tables in the Database (Entity Splitting)

　　映射实体中属性到多张表中

实体 Department 属性 DepartmentID, Name 映射到表 Department;
同时属性 DepartmentID, Administrator, StartDate, Budget 映射到表 DepartmentDetails

// Mapping Properties of an Entity Type to Multiple Tables in the Database (Entity Splitting)

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.Administrator, t.StartDate, t.Budget });

                m.ToTable("DepartmentDetails");

            });

Mapping Multiple Entity Types to One Table in the Database (Table Splitting)

　　映射多个实体到一张表：实体 Instructor 和 OfficeAssignment 映射到同一张表 Instructor

// Mapping Multiple Entity Types to One Table in the Database (Table Splitting)

modelBuilder.Entity<OfficeAssignment>()

            .HasKey(t => t.InstructorID);

modelBuilder.Entity<Instructor>()

            .HasRequired(t => t.OfficeAssignment)

            .WithRequiredPrincipal(t => t.Instructor);

modelBuilder.Entity<Instructor>().ToTable("Instructor");

modelBuilder.Entity<OfficeAssignment>().ToTable("Instructor");

Mapping an Entity Type to Insert/Update/Delete Stored Procedures (EF6 onwards)

　　映射实体到增、改、更、删存储过程，详情请参考文章 http://www.cnblogs.com/panchunting/p/entity-framework-code-first-insert-update-delete-stored-procedures

PS: 关于TPH, TPT, TPC 以后有时间专门写一篇文章介绍

原文参考：http://msdn.microsoft.com/en-us/data/jj591617