EF6学习笔记（六） 创建复杂的数据模型

EF6学习笔记总目录：ASP.NET MVC5 及 EF6 学习笔记 - （目录整理）

本篇原文地址：Creating a More Complex Data Model

本篇讲的比较碎，很多内容本人认为并不是EF的内容，既然原文讲了，那就按照原文来学习吧。。。

第1步：通过属性来定制化数据模型

通过 DataType Attribute来定义数据模型字段属性：

先加申明 using System.ComponentModel.DataAnnotations;

然后为需要定义属性的字段加上属性：（例如EnrollmentDate 加上日期DataType，以及显示格式的属性）

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace EFTest.Models
{
    public class Student
    {
        public int ID { get; set; }
        public string LastName { get; set; }
        public string FirstMidName { get; set; }
        [DataType(DataType.Date)]
        [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
        public DateTime EnrollmentDate { get; set; }

        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }
}

DataType 枚举可以通过 DataType Enumeration链接来查看；主要有用的是：Date,Time,EmailAddress,Password等；
通过DataType定义的数据属性，在应用中得到特殊的数据处理功能，比如Email的话，就在显示的时候自动变为点击发Email的Link;如果Date的话，会在前端自动显示为一个日期输入选择框（在HTML5的情况下）；

但是DataType不提供验证功能，并且也不特别指定显示格式，默认的显示格式基于服务器的CultureInfo

DispalyFormat属性定义就是用来明确定义显示格式；

DisplayFormat可以单独使用，但建议是配合DataType一起使用，配合使用会有以下优点：

1、HTML5支持的浏览器可以根据DataType做出一些特定的调整及显示（比如会显示计算器、日期输入框、Email地址链接等等）

2、默认情况下，浏览器会根据客户端计算机的本地化显示设置来进行渲染（比如本地化的日期时间格式）

3、DataType属性可以让MVC选择正确的字段类型去渲染数据，DisplayFormat使用字符串类型模板；

更多的信息可以参考：MVC 5 Introduction: Examining the Edit Methods and Edit View

通过StringLength 属性定义长度

可以通过StringLength这个属性来定义一个字段的最长长度，并且可以设置出现错误后应该提供的错误信息；

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace EFTest.Models
{
    public class Student
    {
        public int ID { get; set; }
        [StringLength()]
        public string LastName { get; set; }
        [StringLength(, ErrorMessage = "First name 不可以超过50个字符.")]
        public string FirstMidName { get; set; }
        [DataType(DataType.Date)]
        [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
        public DateTime EnrollmentDate { get; set; }

        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }
}

比如设定LastName、FirstMidName最长只能50个字符，并且在FirstMidName输入超过50个字符的时候提示相应错误；
另外，StringLength属性定义不能防止用户输入空格，所以可以通过RegularExpression来进行限制：

[RegularExpression(@"^[A-Z]+[a-zA-Z''-'\s]*$")]

以上这个属性定义，限制首字母为大写，后面也必须为字母；

PS: MaxLength属性定义也能定义字段最大长度，但是并不提供客户端验证。

这个时候如果直接运行应用，并点击Students页面，就会有以下错误：

说明数据模型变了，数据库也需要先升级才可以；

先在PM控制台执行 add-migration MaxLengthOnNames

会自动创建一个带时间戳的数据升级文件；然后在PM控制台继续输入：update-database

完成后，就可以再次尝试进入应用的Student页面，并点击Create进入新建页面：

Column 属性定义：当一些特定情况下，希望数据库里的字段名采用一个约定格式名，而模型中是另一个名称，则需要通过Column来强制换个名字：

首先，添加申明：using System.ComponentModel.DataAnnotations.Schema;

然后用[Column("NewColumnName")] 定义数据库中的列名：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace EFTest.Models
{
    public class Student
    {
        public int ID { get; set; }
        [StringLength()]
        public string LastName { get; set; }
        [StringLength(, ErrorMessage = "First name 不可以超过50个字符.")]
[Column("FirstName")]
public string FirstMidName { get; set; }
        [DataType(DataType.Date)]
        [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
        public DateTime EnrollmentDate { get; set; }

        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }
}

当然，在做了这个改动后，需要今天数据库升级操作：

在PM控制台输入以下命令：
　　add-migration ColumnFirstName
　　update-database

更新后，列名变了，并且DataType从nvarchar(MAX) 变为 nvarchar(50):

PS: 这个操作可以通过 Fluent API 来完成，后面也会提及到。

将Student模型变更为以下完整版本：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace EFTest.Models
{
    public class Student
    {
        public int ID { get; set; }
        [Required]
        [StringLength()]
        [Display(Name = "Last Name")]
        public string LastName { get; set; }
        [Required]
        [StringLength(, ErrorMessage = "First name 不可超过50个字符.")]
        [Column("FirstName")]
        [Display(Name = "First Name")]
        public string FirstMidName { get; set; }
        [DataType(DataType.Date)]
        [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
        [Display(Name = "Enrollment Date")]
        public DateTime EnrollmentDate { get; set; }

        [Display(Name = "Full Name")]
        public string FullName
        {
            get
            {
                return LastName + ", " + FirstMidName;
            }
        }

        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }

}

[Required]对于值类型的是不需要的，例如int , DateTime, double, float ，因为这些值本身是不可以为空NULL的；

对于字符串类型的属性(property)，可以通过设置最小长度来代替[Required]：

[Display(Name = "Last Name")]
[StringLength(, MinimumLength=)]
public string LastName { get; set; }

Display定义在显示View的时候，对应该属性(property)的输入框标题内容；

另外，FullName是一个计算出来的属性(property),所以只有get ,没有set ,这样在数据库里是不会增加 FullName这个列的；

新建Instructor模型：（和Student 模型差不多）

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace EFTest.Models
{
    public class Instructor
    {
        public int ID { get; set; }

        [Required]
        [Display(Name = "Last Name")]
        [StringLength()]
        public string LastName { get; set; }

        [Required]
        [Column("FirstName")]
        [Display(Name = "First Name")]
        [StringLength()]
        public string FirstMidName { get; set; }

        [DataType(DataType.Date)]
        [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
        [Display(Name = "Hire Date")]
        public DateTime HireDate { get; set; }

        [Display(Name = "Full Name")]
        public string FullName
        {
            get { return LastName + ", " + FirstMidName; }
        }

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

}

当然也可以简化属性定义为一行：（通过逗号来分割）

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace EFTest.Models
{
    public class Instructor
    {
        public int ID { get; set; }

        [Display(Name = "Last Name"), StringLength(, MinimumLength = )]
        public string LastName { get; set; }

        [Column("FirstName"), Display(Name = "First Name"), StringLength(, MinimumLength = )]
        public string FirstMidName { get; set; }

        [DataType(DataType.Date), Display(Name = "Hire Date"), DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
        public DateTime HireDate { get; set; }

        [Display(Name = "Full Name")]
        public string FullName
        {
            get { return LastName + ", " + FirstMidName; }
        }

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

    }

}

在Instructor模型中 Courses 和 OfficeAssignment为导航属性，采用virtual来定义为延迟加载；
Instructor对应Courses 是1对n ，所以采用ICollection<T>来表示；

Instructor对应OfficeAssignment是1对1，所以直接采用OfficeAssignment来定义；

新建OfficeAssignment模型：

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace EFTest.Models
{
    public class OfficeAssignment
    {
        [Key]
        [ForeignKey("Instructor")]
        public int InstructorID { get; set; }
        [StringLength()]
        [Display(Name = "Office Location")]
        public string Location { get; set; }

        public virtual Instructor Instructor { get; set; }
    }

}

Instructor对应OfficeAssignment是1对1或者 1对0，即OfficeAssignment表中的InstructorID一定是在Instructor存在这个ID的；

所以对于OfficeAssignment InstructorID需要设置为主键，并且要定义为从Instructor ID来的外键；

修改Course模型

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace EFTest.Models
{
    public class Course
    {
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        [Display(Name = "Number")]
        public int CourseID { get; set; }

        [StringLength(, MinimumLength = )]
        public string Title { get; set; }

        [Range(, )]
        public int Credits { get; set; }

        public int DepartmentID { get; set; }

        public virtual Department Department { get; set; }
        public virtual ICollection<Enrollment> Enrollments { get; set; }
        public virtual ICollection<Instructor> Instructors { get; set; }
    }

}

新建Department模型

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace EFTest.Models
{
    public class Department
    {
        public int DepartmentID { get; set; }

        [StringLength(, MinimumLength = )]
        public string Name { get; set; }

        [DataType(DataType.Currency)]
        [Column(TypeName = "money")]
        public decimal Budget { get; set; }

        [DataType(DataType.Date)]
        [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
        [Display(Name = "Start Date")]
        public DateTime StartDate { get; set; }

        public int? InstructorID { get; set; }

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

}

最后希望的模型定义图：

做些总结汇总：

1、模型中Properties如果名称为ID或者是类名+ID，则EF会自动将其变为主键；

2、如果主键为int型，默认会定义为数据库自增长的类型，除非用 [DatabaseGenerated(DatabaseGeneratedOption.None)] 来明确告知不要；

3、如果是1对1或0的对应关系，需要明确用[ForeignKey("XXXX")]来告知EF哪个是主表哪个是子表，不然会报异常；

4、如果是多对1或0的对应关系，如果Properties是值类型，则需要用 问号 来定义可以为空；

5、默认情况下，EF是开启联级删除(cascade delete)，那么如果外键导致的联级删除出现多个

例如：    A -> B 是 1对多，   A -> C 也是 1对多，  B 和 C 是多对多， 那么要删除 一个A，就需要联级删除先删除 B 和 C ，而要删除B 和 C 就要先删除 B 和 C 连接对应；

这样就有两条路都到删除 B 和 C 的连接关系，这个是数据库所不允许的；

那么只有两种方式：

a) fluent API来申明关闭这个A的cascade delete；

b) 把A -> B设置为 0,1对多，或者  A -> C 设置为 0,1对多， 即删除A时，不是删除B，而是把B里涉及到A的外键列值设置为NULL。

6、如果是多对多的关系，则EF会自动新建一个表来存储多对多的关系；

在上下文类中通过Fluent API来定义复杂模型关系及一些设定

在上下文类中增加定义所有的实体，并通过Fluent API来定义一些设定；

Fluent API可以用来设定绝大部分的模型关系及定义，但是也有一些不可以用Fluent API来设定，比如 MinimumLength

因为MinimumLength 不会对数据库结构产生影响，而只是对客户端验证起作用；

有点程序员比较喜欢用Fluent API，这样模型定义看起来“干净”很多，也可以用属性定义和Fluent API混合起来使用；

以下的Fluent API定义了多对多的连接关系所采用的表名：

using EFTest.Models;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;

namespace EFTest.DAL
{
    public class SchoolContext : DbContext
    {
        public SchoolContext() : base("SchoolContext")
        {
        }
        public DbSet<Student> Students { get; set; }
        public DbSet<Enrollment> Enrollments { get; set; }
        public DbSet<Course> Courses { get; set; }
        public DbSet<Instructor> Instructors { get; set; }
        public DbSet<Department> Departments { get; set; }
        public DbSet<OfficeAssignment> OfficeAssignments { get; set; }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
            modelBuilder.Entity<Course>()
                    .HasMany(c => c.Instructors).WithMany(i => i.Courses)
                    .Map(t => t.MapLeftKey("CourseID")
                    .MapRightKey("InstructorID")
                    .ToTable("CourseInstructor"));
        }
    }
}

初始化种子数据

模型调整好后，在Migrations\Configuration.cs文件中Seed方法中放入测试种子数据：

namespace EFTest.Migrations
{
    using DAL;
    using Models;
    using System;
    using System.Collections.Generic;
    using System.Data.Entity;
    using System.Data.Entity.Migrations;
    using System.Linq;

    internal sealed class Configuration : DbMigrationsConfiguration<EFTest.DAL.SchoolContext>
    {
        public Configuration()
        {
            AutomaticMigrationsEnabled = false;
        }

        protected override void Seed(EFTest.DAL.SchoolContext context)
        {
            var students = new List<Student>
            {
                new Student { FirstMidName = "Carson",   LastName = "Alexander",
                    EnrollmentDate = DateTime.Parse("2010-09-01") },
                new Student { FirstMidName = "Meredith", LastName = "Alonso",
                    EnrollmentDate = DateTime.Parse("2012-09-01") },
                new Student { FirstMidName = "Arturo",   LastName = "Anand",
                    EnrollmentDate = DateTime.Parse("2013-09-01") },
                new Student { FirstMidName = "Gytis",    LastName = "Barzdukas",
                    EnrollmentDate = DateTime.Parse("2012-09-01") },
                new Student { FirstMidName = "Yan",      LastName = "Li",
                    EnrollmentDate = DateTime.Parse("2012-09-01") },
                new Student { FirstMidName = "Peggy",    LastName = "Justice",
                    EnrollmentDate = DateTime.Parse("2011-09-01") },
                new Student { FirstMidName = "Laura",    LastName = "Norman",
                    EnrollmentDate = DateTime.Parse("2013-09-01") },
                new Student { FirstMidName = "Nino",     LastName = "Olivetto",
                    EnrollmentDate = DateTime.Parse("2005-09-01") }
            };

            students.ForEach(s => context.Students.AddOrUpdate(p => p.LastName, s));
            context.SaveChanges();

            var instructors = new List<Instructor>
            {
                new Instructor { FirstMidName = "Kim",     LastName = "Abercrombie",
                    HireDate = DateTime.Parse("1995-03-11") },
                new Instructor { FirstMidName = "Fadi",    LastName = "Fakhouri",
                    HireDate = DateTime.Parse("2002-07-06") },
                new Instructor { FirstMidName = "Roger",   LastName = "Harui",
                    HireDate = DateTime.Parse("1998-07-01") },
                new Instructor { FirstMidName = "Candace", LastName = "Kapoor",
                    HireDate = DateTime.Parse("2001-01-15") },
                new Instructor { FirstMidName = "Roger",   LastName = "Zheng",
                    HireDate = DateTime.Parse("2004-02-12") }
            };
            instructors.ForEach(s => context.Instructors.AddOrUpdate(p => p.LastName, s));
            context.SaveChanges();

            var departments = new List<Department>
            {
                new Department { Name = "English",     Budget = ,
                    StartDate = DateTime.Parse("2007-09-01"),
                    InstructorID  = instructors.Single( i => i.LastName == "Abercrombie").ID },
                new Department { Name = "Mathematics", Budget = ,
                    StartDate = DateTime.Parse("2007-09-01"),
                    InstructorID  = instructors.Single( i => i.LastName == "Fakhouri").ID },
                new Department { Name = "Engineering", Budget = ,
                    StartDate = DateTime.Parse("2007-09-01"),
                    InstructorID  = instructors.Single( i => i.LastName == "Harui").ID },
                new Department { Name = "Economics",   Budget = ,
                    StartDate = DateTime.Parse("2007-09-01"),
                    InstructorID  = instructors.Single( i => i.LastName == "Kapoor").ID }
            };
            departments.ForEach(s => context.Departments.AddOrUpdate(p => p.Name, s));
            context.SaveChanges();

            var courses = new List<Course>
            {
                new Course {CourseID = , Title = "Chemistry",      Credits = ,
                  DepartmentID = departments.Single( s => s.Name == "Engineering").DepartmentID,
                  Instructors = new List<Instructor>()
                },
                new Course {CourseID = , Title = "Microeconomics", Credits = ,
                  DepartmentID = departments.Single( s => s.Name == "Economics").DepartmentID,
                  Instructors = new List<Instructor>()
                },
                new Course {CourseID = , Title = "Macroeconomics", Credits = ,
                  DepartmentID = departments.Single( s => s.Name == "Economics").DepartmentID,
                  Instructors = new List<Instructor>()
                },
                new Course {CourseID = , Title = "Calculus",       Credits = ,
                  DepartmentID = departments.Single( s => s.Name == "Mathematics").DepartmentID,
                  Instructors = new List<Instructor>()
                },
                new Course {CourseID = , Title = "Trigonometry",   Credits = ,
                  DepartmentID = departments.Single( s => s.Name == "Mathematics").DepartmentID,
                  Instructors = new List<Instructor>()
                },
                new Course {CourseID = , Title = "Composition",    Credits = ,
                  DepartmentID = departments.Single( s => s.Name == "English").DepartmentID,
                  Instructors = new List<Instructor>()
                },
                new Course {CourseID = , Title = "Literature",     Credits = ,
                  DepartmentID = departments.Single( s => s.Name == "English").DepartmentID,
                  Instructors = new List<Instructor>()
                },
            };
            courses.ForEach(s => context.Courses.AddOrUpdate(p => p.CourseID, s));
            context.SaveChanges();

            var officeAssignments = new List<OfficeAssignment>
            {
                new OfficeAssignment {
                    InstructorID = instructors.Single( i => i.LastName == "Fakhouri").ID,
                    Location = "Smith 17" },
                new OfficeAssignment {
                    InstructorID = instructors.Single( i => i.LastName == "Harui").ID,
                    Location = "Gowan 27" },
                new OfficeAssignment {
                    InstructorID = instructors.Single( i => i.LastName == "Kapoor").ID,
                    Location = "Thompson 304" },
            };
            officeAssignments.ForEach(s => context.OfficeAssignments.AddOrUpdate(p => p.InstructorID, s));
            context.SaveChanges();

            AddOrUpdateInstructor(context, "Chemistry", "Kapoor");
            AddOrUpdateInstructor(context, "Chemistry", "Harui");
            AddOrUpdateInstructor(context, "Microeconomics", "Zheng");
            AddOrUpdateInstructor(context, "Macroeconomics", "Zheng");

            AddOrUpdateInstructor(context, "Calculus", "Fakhouri");
            AddOrUpdateInstructor(context, "Trigonometry", "Harui");
            AddOrUpdateInstructor(context, "Composition", "Abercrombie");
            AddOrUpdateInstructor(context, "Literature", "Abercrombie");

            context.SaveChanges();

            var enrollments = new List<Enrollment>
            {
                new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Alexander").ID,
                    CourseID = courses.Single(c => c.Title == "Chemistry" ).CourseID,
                    Grade = Grade.A
                },
                 new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Alexander").ID,
                    CourseID = courses.Single(c => c.Title == "Microeconomics" ).CourseID,
                    Grade = Grade.C
                 },
                 new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Alexander").ID,
                    CourseID = courses.Single(c => c.Title == "Macroeconomics" ).CourseID,
                    Grade = Grade.B
                 },
                 new Enrollment {
                     StudentID = students.Single(s => s.LastName == "Alonso").ID,
                    CourseID = courses.Single(c => c.Title == "Calculus" ).CourseID,
                    Grade = Grade.B
                 },
                 new Enrollment {
                     StudentID = students.Single(s => s.LastName == "Alonso").ID,
                    CourseID = courses.Single(c => c.Title == "Trigonometry" ).CourseID,
                    Grade = Grade.B
                 },
                 new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Alonso").ID,
                    CourseID = courses.Single(c => c.Title == "Composition" ).CourseID,
                    Grade = Grade.B
                 },
                 new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Anand").ID,
                    CourseID = courses.Single(c => c.Title == "Chemistry" ).CourseID
                 },
                 new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Anand").ID,
                    CourseID = courses.Single(c => c.Title == "Microeconomics").CourseID,
                    Grade = Grade.B
                 },
                new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Barzdukas").ID,
                    CourseID = courses.Single(c => c.Title == "Chemistry").CourseID,
                    Grade = Grade.B
                 },
                 new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Li").ID,
                    CourseID = courses.Single(c => c.Title == "Composition").CourseID,
                    Grade = Grade.B
                 },
                 new Enrollment {
                    StudentID = students.Single(s => s.LastName == "Justice").ID,
                    CourseID = courses.Single(c => c.Title == "Literature").CourseID,
                    Grade = Grade.B
                 }
            };

            foreach (Enrollment e in enrollments)
            {
                var enrollmentInDataBase = context.Enrollments.Where(
                    s =>
                         s.Student.ID == e.StudentID &&
                         s.Course.CourseID == e.CourseID).SingleOrDefault();
                if (enrollmentInDataBase == null)
                {
                    context.Enrollments.Add(e);
                }
            }
            context.SaveChanges();

        }

        void AddOrUpdateInstructor(SchoolContext context, string courseTitle, string instructorName)
        {
            var crs = context.Courses.SingleOrDefault(c => c.Title == courseTitle);
            var inst = crs.Instructors.SingleOrDefault(i => i.LastName == instructorName);
            if (inst == null)
                crs.Instructors.Add(context.Instructors.Single(i => i.LastName == instructorName));
        }
    }
}

数据库迁移升级

在PM控制台输入： add-Migration ComplexDataModel

这个时候如果直接输入 update-database  会报错，那是因为Course这个表里已经有数据，如果直接加不可为空的列是会报错的；

所以需要在刚刚生成的带时间戳的 XXXXXXXXXXX_ComplexDataModel文件中如下面增加修改部分代码：

即先插入一条临时的Department ，然后把现在所有的Course数据行在增加Department列的时候，指向这个临时Department.

                CreateTable(
                "dbo.CourseInstructor",
                c => new
                    {
                        CourseID = c.Int(nullable: false),
                        InstructorID = c.Int(nullable: false),
                    })
                .PrimaryKey(t => new { t.CourseID, t.InstructorID })
                .ForeignKey("dbo.Course", t => t.CourseID, cascadeDelete: true)
                .ForeignKey("dbo.Instructor", t => t.InstructorID, cascadeDelete: true)
                .Index(t => t.CourseID)
                .Index(t => t.InstructorID);

            // Create  a department for course to point to.
            Sql("INSERT INTO dbo.Department (Name, Budget, StartDate) VALUES ('Temp', 0.00, GETDATE())");
            //  default value for FK points to department created above.
            AddColumn("dbo.Course", "DepartmentID", c => c.Int(nullable: false, defaultValue: 1));
            //AddColumn("dbo.Course", "DepartmentID", c => c.Int(nullable: false));

            AlterColumn("dbo.Course", "Title", c => c.String(maxLength: ));

最后执行 update-database 即可。