如何手动（通过代码）应用手工制作的DbMigration？

Question

我手动创建一个类

public class AddClientsTable : DbMigration, IMigrationMetadata 
    { 

    string IMigrationMetadata.Id 
    { 
     get { return "201611281757258_AddClientsTable"; } 
    } 

    string IMigrationMetadata.Source 
    { 
     get { return null; } 
    } 

    string IMigrationMetadata.Target 
    { 
     get { return "AddClientsTable-Migration"; } 
    } 

    public override void Up() { 
     CreateTable("Clients", t => new { 
      ClientId = t.Guid(name:"ClientId"), 
      Name = t.String() 
      }) 
     .PrimaryKey(t => t.ClientId, "ClientId") 
     .Index(t => t.ClientId, "PK_Clients", true); 
    } 

    public override void Down() { 
     DropIndex("Clients", "PK_Clients"); 
     DropTable("Clients"); 
    } 

    } 

，我想通过代码优先迁移从代码应用这样的：

 var migration = new AddClientsTable(); 
     migration.Up(); 
     context.RunMigration(migration); 

这是我从here偷走了，但是当我运行的代码我得到这个例外：

Unable to cast object of type 'System.Data.Entity.Migrations.Model.CreateIndexOperation' to type 'System.Data.Entity.Migrations.Model.HistoryOperation'. 

HistoryOperation是操作w更新__MigrationHistory表？所以我如何通过代码来做到这一点？

我缺少的东西或EntityFrameowrk Update-Database命令确实比我知道的更多？

Answer 1

这是没有意义的樱桃采摘迁移并运行它，因为迁移是累积的，必须按顺序运行。因此，您最好在应用程序启动时运行相当于update-database powershell的命令。

下面是一些代码，我们用它来做到这一点：

在Configuration.cs类的构造函数

AutomaticMigrationsEnabled = false; 
AutomaticMigrationDataLossAllowed = false; 

然后在应用程序启动时调用下面的方法（当你enable-migrations这个文件发）：

public static void ApplyDatabaseMigrations() 
{ 
    //Configuration is the class created by Enable-Migrations 
    DbMigrationsConfiguration dbMgConfig = new Configuration() 
    { 
     ContextType = typeof(MyDbContext) //+++++CHANGE ME+++++ 
    }; 
    using (var databaseContext = new MyDbContext()) //+++++CHANGE ME+++++ 
    { 
     try 
     { 
      var database = databaseContext.Database; 
      var migrationConfiguration = dbMgConfig; 
      migrationConfiguration.TargetDatabase = 
       new DbConnectionInfo(database.Connection.ConnectionString, 
            "System.Data.SqlClient"); 
      var migrator = new DbMigrator(migrationConfiguration); 
      migrator.Update(); 
     } 
     catch (AutomaticDataLossException adle) 
     { 
      dbMgConfig.AutomaticMigrationDataLossAllowed = true; 
      var mg = new DbMigrator(dbMgConfig); 
      var scriptor = new MigratorScriptingDecorator(mg); 
      string script = scriptor.ScriptUpdate(null, null); 
      throw new Exception(adle.Message + " : " + script); 
     } 
    } 
}