EF CodeFirst 如何通過配置自動創建數據庫當模型改變時

? ?最近悟出來一個道理，在這兒分享給大家：學歷代表你的過去，能力代表你的現在，學習代表你的將來。

???十年河東十年河西，莫欺少年窮

???學無止境，精益求精

? ?本篇為進階篇，也是彌補自己之前沒搞明白的地方,慚愧慚愧。

? ?如有不明白，請參考：EF CodeFirst 創建數據庫?及?EF CodeFirst增刪改查之‘CRUD’

? ?話不多說，直接上代碼：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;namespace EF_Test.DAL
{public class StudentInitializer : System.Data.Entity.DropCreateDatabaseIfModelChanges<StudentContext>{protected override void Seed(StudentContext context){//添加學生var studentList = new List<Student>{new Student{Name = "陳依依", Sex = "女", StudentNum = "081309201"},new Student{Name = "戚永景", Sex = "女", StudentNum = "081309202"},new Student{Name = "劉華麗", Sex = "女", StudentNum = "081309203"},new Student{Name = "薛正欽", Sex = "男", StudentNum = "081309204"},new Student{Name = "王松濤", Sex = "男", StudentNum = "081309205"},new Student{Name = "王自龍", Sex = "男", StudentNum = "081309206"},new Student{Name = "高其峰", Sex = "男", StudentNum = "081309207"},new Student{Name = "陳欣欣", Sex = "女", StudentNum = "081309208"},new Student{Name = "陳麗陽", Sex = "女", StudentNum = "081309209"}};studentList.ForEach(s => context.Students.Add(s));context.SaveChanges();//添加課程var courseList = new List<Course>{new Course{ Name="數據結構"},new Course{ Name="計算機原理"},new Course{ Name="網絡技術"}};courseList.ForEach(s => context.Courses.Add(s));context.SaveChanges();//添加分數var scoreList = new List<Score>(){new Score{ StudentID=1,CourseID=1,StudentScore=90},new Score{ StudentID=2,CourseID=1,StudentScore=91},new Score{ StudentID=3,CourseID=1,StudentScore=92},new Score{ StudentID=4,CourseID=1,StudentScore=93},new Score{ StudentID=5,CourseID=1,StudentScore=94},new Score{ StudentID=6,CourseID=1,StudentScore=95},new Score{ StudentID=7,CourseID=1,StudentScore=96},new Score{ StudentID=8,CourseID=1,StudentScore=97},new Score{ StudentID=9,CourseID=1,StudentScore=98}};scoreList.ForEach(s => context.Scores.Add(s));context.SaveChanges();}}
}

?

? ?模型類如下：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;
using System.Linq;
using System.Web;namespace EF_Test.DAL
{public class Student{[Key]public int Id { get; set; }[Required][StringLength(10)]public string Name { get; set; }//姓名[StringLength(2)]public string Sex { get; set; }//性別[StringLength(20)]public string StudentNum { get; set; }//學號
    }public class Course{[Key]public int Id { get; set; }[Required][StringLength(20)]public string Name { get; set; }//課程名稱
    }public class Score{[Key]public int Id { get; set; }public int StudentScore { get; set; }//學生分數public int StudentID { get; set; }//學生IDpublic int CourseID { get; set; }//課程IDpublic virtual Student Student { get; set; }//virtual關鍵字修飾，用于延遲加載 提高性能 只有顯式調用時  屬性==對象public virtual Course Course { get; set; }//virtual關鍵字修飾，用于延遲加載 提高性能 只有顯式調用時  屬性==對象
    }public class StudentContext : DbContext{public StudentContext(): base("StudentContext")//指定連接字符串
        {}public DbSet<Student> Students { get; set; }public DbSet<Course> Courses { get; set; }public DbSet<Score> Scores { get; set; }/// <summary>/// OnModelCreating方法中的modelBuilder.Conventions.Remove語句禁止表名稱正在多元化。如果你不這樣做，所生成的表將命名為Students、Courses和Enrollments。相反，表名稱將是Student、Course和Enrollment。開發商不同意關于表名稱應該多數。本教程使用的是單數形式，但重要的一點是，您可以選擇哪個你更喜歡通過包括或省略這行代碼的形式。/// </summary>/// <param name="modelBuilder"></param>protected override void OnModelCreating(DbModelBuilder modelBuilder){modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();}}
}

? ?OK，截止到這兒，您可能會問我，protected override void Seed（）這個重寫的方法什么時間執行呢？

? ?在此，需要兩點要求

? ?1、在web.config中<entityFramework>接點下加入如下配置：

    <contexts><context type="EF_Test.DAL.StudentContext, EF_Test"><databaseInitializer type="EF_Test.DAL.StudentInitializer, EF_Test" /></context></contexts>

? ?根據上述類文件，我們應該明白EF_Test是個命名空間，EF_Test.DAL.StudentContext是數據庫上下文，EF_Test.DAL.StudentInitializer是初始化類

? ?2、加上了上述配置，還需模型結構發生改變時，程序才會自動執行Seed()方法，例如：將字段長度由50改為20

? ?綜上所述條件滿足后，程序就會自動重新刪除數據庫并建立

? ?@陳臥龍的博客

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