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(数据库迁移原理)
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时间：2015年06月12日
1. 关于EntityFramework数据迁移原理
查询数据库的表"__MigrationHistory"，遍历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：
1 public class Blog 2 { 3 public int BlogId { get; set; } 4 public string Name { get; set; } 5 6 public string Url { get; set; } 7 public virtual List<Post> Posts { get; set; } 8 } 9 10 public class User 11 { 12 [Key] 13 public int UserId { get; set; } 14 public string Username { get; set; } 15 public string DisplayName { get; set; } 16 //public int? age { get; set; } 17 //public string interest { get; set; } 18 } 19 20 public class School 21 { 22 public int SchoolId { get; set; } 23 24 public string SchoolName { get; set; } 25 26 public int SchoolLevel { get; set; } 27 } 28 29 30 public class Teacher 31 { 32 [Key] 33 public int TecherId { get; set; } 34 public string TeacherName { get; set; } 35 } 36 37 38 public class Post 39 { 40 public int PostId { get; set; } 41 public string Title { get; set; } 42 public string Content { get; set; } 43 44 public int BlogId { get; set; } 45 public virtual Blog Blog { get; set; } 46 } 47 48 public class Tutorial 49 { 50 [Key] 51 public int Id { get; set; } 52 53 public int Name { get; set; } 54 } 55 56 public class BloggingContext : DbContext 57 { 58 public DbSet<Blog> Blogs { get; set; } 59 public DbSet<Post> Posts { get; set; } 60 61 public DbSet<User> Users { get; set; } 62 63 public DbSet<Tutorial> Tutorials { get; set; } 64 public DbSet<School> Schools { get; set; } 65 66 public DbSet<Teacher> Teachers { get; set; } 67 protected override void OnModelCreating(DbModelBuilder modelBuilder) 68 { 69 modelBuilder.Entity<User>().Property(u => u.DisplayName).HasColumnName("display_name"); 70 modelBuilder.Entity<User>().Property(u => u.Username).HasColumnName("user_name"); 71 } 72 }
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，
1 public partial class addmodels : DbMigration 2 { 3 public override void Up() 4 { 5 CreateTable( 6 "dbo.Blogs", 7 c => new 8 { 9 BlogId = c.Int(nullable: false, identity: true), 10 Name = c.String(), 11 Url = c.String(), 12 }) 13 .PrimaryKey(t => t.BlogId); 14 15 CreateTable( 16 "dbo.Posts", 17 c => new 18 { 19 PostId = c.Int(nullable: false, identity: true), 20 Title = c.String(), 21 Content = c.String(), 22 BlogId = c.Int(nullable: false), 23 }) 24 .PrimaryKey(t => t.PostId) 25 .ForeignKey("dbo.Blogs", t => t.BlogId, cascadeDelete: true) 26 .Index(t => t.BlogId); 27 28 CreateTable( 29 "dbo.Schools", 30 c => new 31 { 32 SchoolId = c.Int(nullable: false, identity: true), 33 SchoolName = c.String(), 34 SchoolLevel = c.Int(nullable: false), 35 }) 36 .PrimaryKey(t => t.SchoolId); 37 38 CreateTable( 39 "dbo.Tutorials", 40 c => new 41 { 42 Id = c.Int(nullable: false, identity: true), 43 Name = c.Int(nullable: false), 44 }) 45 .PrimaryKey(t => t.Id); 46 47 CreateTable( 48 "dbo.Users", 49 c => new 50 { 51 UserId = c.Int(nullable: false, identity: true), 52 user_name = c.String(), 53 display_name = c.String(), 54 }) 55 .PrimaryKey(t => t.UserId); 56 57 } 58 59 public override void Down() 60 { 61 DropForeignKey("dbo.Posts", "BlogId", "dbo.Blogs"); 62 DropIndex("dbo.Posts", new[] { "BlogId" }); 63 DropTable("dbo.Users"); 64 DropTable("dbo.Tutorials"); 65 DropTable("dbo.Schools"); 66 DropTable("dbo.Posts"); 67 DropTable("dbo.Blogs"); 68 } 69 }
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
1 public partial class addmodels : DbMigration 2 { 3 public override void Up() 4 { 5 //CreateTable( 6 // "dbo.Blogs", 7 // c => new 8 // { 9 // BlogId = c.Int(nullable: false, identity: true), 10 // Name = c.String(), 11 // Url = c.String(), 12 // }) 13 // .PrimaryKey(t => t.BlogId); 14 15 //CreateTable( 16 // "dbo.Posts", 17 // c => new 18 // { 19 // PostId = c.Int(nullable: false, identity: true), 20 // Title = c.String(), 21 // Content = c.String(), 22 // BlogId = c.Int(nullable: false), 23 // }) 24 // .PrimaryKey(t => t.PostId) 25 // .ForeignKey("dbo.Blogs", t => t.BlogId, cascadeDelete: true) 26 // .Index(t => t.BlogId); 27 28 CreateTable( 29 "dbo.Schools", 30 c => new 31 { 32 SchoolId = c.Int(nullable: false, identity: true), 33 SchoolName = c.String(), 34 SchoolLevel = c.Int(nullable: false), 35 }) 36 .PrimaryKey(t => t.SchoolId); 37 38 //CreateTable( 39 // "dbo.Tutorials", 40 // c => new 41 // { 42 // Id = c.Int(nullable: false, identity: true), 43 // Name = c.Int(nullable: false), 44 // }) 45 // .PrimaryKey(t => t.Id); 46 47 //CreateTable( 48 // "dbo.Users", 49 // c => new 50 // { 51 // UserId = c.Int(nullable: false, identity: true), 52 // user_name = c.String(), 53 // display_name = c.String(), 54 // }) 55 // .PrimaryKey(t => t.UserId); 56 57 } 58 59 public override void Down() 60 { 61 //DropForeignKey("dbo.Posts", "BlogId", "dbo.Blogs"); 62 //DropIndex("dbo.Posts", new[] { "BlogId" }); 63 //DropTable("dbo.Users"); 64 //DropTable("dbo.Tutorials"); 65 DropTable("dbo.Schools"); 66 //DropTable("dbo.Posts"); 67 //DropTable("dbo.Blogs"); 68 } 69 }
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
DECLARE @CurrentMigration [nvarchar](max) IF object_id(‘[dbo].[__MigrationHistory]‘) IS NOT NULL SELECT @CurrentMigration = (SELECT TOP (1) [Project1].[MigrationId] AS [MigrationId] FROM ( SELECT [Extent1].[MigrationId] AS [MigrationId] FROM [dbo].[__MigrationHistory] AS [Extent1] WHERE [Extent1].[ContextKey] = N‘EntityFrameworkStudy.Migrations.Configuration‘ ) AS [Project1] ORDER BY [Project1].[MigrationId] DESC) IF @CurrentMigration IS NULL SET @CurrentMigration = ‘0‘ IF @CurrentMigration < ‘201503190906406_addmodels‘ BEGIN CREATE TABLE [dbo].[Blogs] ( [BlogId] [int] NOT NULL IDENTITY, [Name] [nvarchar](max), [Url] [nvarchar](max), CONSTRAINT [PK_dbo.Blogs] PRIMARY KEY ([BlogId]) ) CREATE TABLE [dbo].[Posts] ( [PostId] [int] NOT NULL IDENTITY, [Title] [nvarchar](max), [Content] [nvarchar](max), [BlogId] [int] NOT NULL, CONSTRAINT [PK_dbo.Posts] PRIMARY KEY ([PostId]) ) CREATE INDEX [IX_BlogId] ON [dbo].[Posts]([BlogId]) CREATE TABLE [dbo].[Schools] ( [SchoolId] [int] NOT NULL IDENTITY, [SchoolName] [nvarchar](max), [SchoolLevel] [int] NOT NULL, CONSTRAINT [PK_dbo.Schools] PRIMARY KEY ([SchoolId]) ) CREATE TABLE [dbo].[Teachers] ( [TecherId] [int] NOT NULL IDENTITY, [TeacherName] [nvarchar](max), CONSTRAINT [PK_dbo.Teachers] PRIMARY KEY ([TecherId]) ) CREATE TABLE [dbo].[Tutorials] ( [Id] [int] NOT NULL IDENTITY, [Name] [int] NOT NULL, CONSTRAINT [PK_dbo.Tutorials] PRIMARY KEY ([Id]) ) CREATE TABLE [dbo].[Users] ( [UserId] [int] NOT NULL IDENTITY, [user_name] [nvarchar](max), [display_name] [nvarchar](max), CONSTRAINT [PK_dbo.Users] PRIMARY KEY ([UserId]) ) ALTER TABLE [dbo].[Posts] ADD CONSTRAINT [FK_dbo.Posts_dbo.Blogs_BlogId] FOREIGN KEY ([BlogId]) REFERENCES [dbo].[Blogs] ([BlogId]) ON DELETE CASCADE CREATE TABLE [dbo].[__MigrationHistory] ( [MigrationId] [nvarchar](150) NOT NULL, [ContextKey] [nvarchar](300) NOT NULL, [Model] [varbinary](max) NOT NULL, [ProductVersion] [nvarchar](32) NOT NULL, CONSTRAINT [PK_dbo.__MigrationHistory] PRIMARY KEY ([MigrationId], [ContextKey]) ) INSERT [dbo].[__MigrationHistory]([MigrationId], [ContextKey], [Model], [ProductVersion]) VALUES (N‘201503190906406_addmodels‘, N‘EntityFrameworkStudy.Migrations.Configuration‘, 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, N‘6.1.3-40302‘) END
我找到了Schools的创建SQL , 在数据库中执行即可：
1 CREATE TABLE [dbo].[Schools] ( 2 [SchoolId] [int] NOT NULL IDENTITY, 3 [SchoolName] [nvarchar](max), 4 [SchoolLevel] [int] NOT NULL, 5 CONSTRAINT [PK_dbo.Schools] PRIMARY KEY ([SchoolId]) 6 )
这样你就恢复好了
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