Entity framework 意外删除了表，如何在不影响其它表的情况下恢复回来

关于EntityFramework数据迁移原理

查询数据库的表"__MigrationHistory"，遍历代码库的Migrations文件夹下的所有文件，如果文件不在__MigrationHistory表内，那么就执行迁移。

有了上面的原理之后，我们来看一下如果我们不小心手动删除了一个表，如何在不影响其它表的情况下来恢复你删除的表：

方法一：

关于Model 以及 DBContext如下：

   public class Blog
    {
        public int BlogId { get; set; }
        public string Name { get; set; }

        public string Url { get; set; }
        public virtual List<Post> Posts { get; set; }
    }

    public class User
    {
        [Key]
        public int UserId { get; set; }
        public string Username { get; set; }
        public string DisplayName { get; set; }
        //public int? age { get; set; }
        //public string interest { get; set; }
    }

    public class School
    {
        public int SchoolId { get; set; }

        public string SchoolName { get; set; }

        public int SchoolLevel { get; set; }
    }

    public class Teacher
    {
        [Key]
        public int TecherId { get; set; }
        public string TeacherName { get; set; }
    }

    public class Post
    {
        public int PostId { get; set; }
        public string Title { get; set; }
        public string Content { get; set; }

        public int BlogId { get; set; }
        public virtual Blog Blog { get; set; }
    }

    public class Tutorial
    {
        [Key]
        public int Id { get; set; }

        public int Name { get; set; }
    }

    public class BloggingContext : DbContext
    {
        public DbSet<Blog> Blogs { get; set; }
        public DbSet<Post> Posts { get; set; }

        public DbSet<User> Users { get; set; }

        public DbSet<Tutorial> Tutorials { get; set; }
        public DbSet<School> Schools { get; set; }

        public DbSet<Teacher> Teachers { get; set; }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<User>().Property(u => u.DisplayName).HasColumnName("display_name");
            modelBuilder.Entity<User>().Property(u => u.Username).HasColumnName("user_name");
        }
    }

　　

migrations 文件夹下的文件如下：

对应数据库中的记录为：

假如此时我们手动删除了schools表，此时我们应该找到schools表的创建与修改的迁移code是在哪个Migrations文件夹下面的哪个文件，找到对应的文件

我们这里是在201503190341085_addmodels.cs中，

   public partial class addmodels : DbMigration
     {
         public override void Up()
         {
             CreateTable(
                 "dbo.Blogs",
                 c => new
                     {
                         BlogId = c.Int(nullable: false, identity: true),
                         Name = c.String(),
                         Url = c.String(),
                     })
                 .PrimaryKey(t => t.BlogId);

             CreateTable(
                 "dbo.Posts",
                 c => new
                     {
                         PostId = c.Int(nullable: false, identity: true),
                         Title = c.String(),
                         Content = c.String(),
                         BlogId = c.Int(nullable: false),
                     })
                 .PrimaryKey(t => t.PostId)
                 .ForeignKey("dbo.Blogs", t => t.BlogId, cascadeDelete: true)
                 .Index(t => t.BlogId);

             CreateTable(
                 "dbo.Schools",
                 c => new
                     {
                         SchoolId = c.Int(nullable: false, identity: true),
                         SchoolName = c.String(),
                         SchoolLevel = c.Int(nullable: false),
                     })
                 .PrimaryKey(t => t.SchoolId);

             CreateTable(
                 "dbo.Tutorials",
                 c => new
                     {
                         Id = c.Int(nullable: false, identity: true),
                         Name = c.Int(nullable: false),
                     })
                 .PrimaryKey(t => t.Id);

             CreateTable(
                 "dbo.Users",
                 c => new
                     {
                         UserId = c.Int(nullable: false, identity: true),
                         user_name = c.String(),
                         display_name = c.String(),
                     })
                 .PrimaryKey(t => t.UserId);

         }

         public override void Down()
         {
             DropForeignKey("dbo.Posts", "BlogId", "dbo.Blogs");
             DropIndex("dbo.Posts", new[] { "BlogId" });
             DropTable("dbo.Users");
             DropTable("dbo.Tutorials");
             DropTable("dbo.Schools");
             DropTable("dbo.Posts");
             DropTable("dbo.Blogs");
         }
     }

　　

此时我们要做的只要把这个文件名201503190341085_addmodels.cs对应在数据迁移表中的记录删除，

delete __MigrationHistory where MigrationId = '201503190341085_addmodels' ,然后我们在201503190341085_addmodels.cs注释掉其它的迁移数据，只留下创建shools表的数据

    public partial class addmodels : DbMigration
    {
        public override void Up()
        {
            //CreateTable(
            //    "dbo.Blogs",
            //    c => new
            //        {
            //            BlogId = c.Int(nullable: false, identity: true),
            //            Name = c.String(),
            //            Url = c.String(),
            //        })
            //    .PrimaryKey(t => t.BlogId);

            //CreateTable(
            //    "dbo.Posts",
            //    c => new
            //        {
            //            PostId = c.Int(nullable: false, identity: true),
            //            Title = c.String(),
            //            Content = c.String(),
            //            BlogId = c.Int(nullable: false),
            //        })
            //    .PrimaryKey(t => t.PostId)
            //    .ForeignKey("dbo.Blogs", t => t.BlogId, cascadeDelete: true)
            //    .Index(t => t.BlogId);

            CreateTable(
                "dbo.Schools",
                c => new
                    {
                        SchoolId = c.Int(nullable: false, identity: true),
                        SchoolName = c.String(),
                        SchoolLevel = c.Int(nullable: false),
                    })
                .PrimaryKey(t => t.SchoolId);

            //CreateTable(
            //    "dbo.Tutorials",
            //    c => new
            //        {
            //            Id = c.Int(nullable: false, identity: true),
            //            Name = c.Int(nullable: false),
            //        })
            //    .PrimaryKey(t => t.Id);

            //CreateTable(
            //    "dbo.Users",
            //    c => new
            //        {
            //            UserId = c.Int(nullable: false, identity: true),
            //            user_name = c.String(),
            //            display_name = c.String(),
            //        })
            //    .PrimaryKey(t => t.UserId);

        }

        public override void Down()
        {
            //DropForeignKey("dbo.Posts", "BlogId", "dbo.Blogs");
            //DropIndex("dbo.Posts", new[] { "BlogId" });
            //DropTable("dbo.Users");
            //DropTable("dbo.Tutorials");
            DropTable("dbo.Schools");
            //DropTable("dbo.Posts");
            //DropTable("dbo.Blogs");
        }
    }

　　

此时如果你在package-manager console 中执行update-database 即可完成schools表的恢复

方法二：

利用 Update-Database -Script -SourceMigration $InitialDatabase （这是一个变量不需要你去改成你自己的数据库名字）  或者

Update-Database -Script -SourceMigration Second -TargetMigration First (用这两个中的哪个是视情况而定的)
(Second First 就是你的migrations文件夹下的文件名字的后面那个 比喻 201503190906406_addmodels 你就输入 Update-Database -Script -SourceMigration addmodels)

这样会产生一个脚本文件，你在那个脚本文件中找出你恢复的表的一些创建或者修改信息

我找到了Schools的创建SQL ,　在数据库中执行即可：

CREATE TABLE [dbo].[Schools] (
[SchoolId] [int] NOT NULL IDENTITY,
[SchoolName] [nvarchar](max),
[SchoolLevel] [int] NOT NULL,
CONSTRAINT [PK_dbo.Schools] PRIMARY KEY ([SchoolId])
)

　　

这样你就恢复好了