3：運(yùn)行命令Enable-Migrations
可能會出現(xiàn)如下錯誤：
Checking if the context targets an existing database...
Detected database created with a database initializer. Scaffolded migration '201212090821166_InitialCreate' corresponding to existing database. To use an automatic migration instead, delete the Migrations folder and re-run Enable-Migrations specifying the -EnableAutomaticMigrations parameter.
Code First Migrations enabled for project MvcApplication1.
此時項目會出現(xiàn)如下文件夾：
打開configuation.cs，將作出如下修改：
public Configuration()
{
AutomaticMigrationsEnabled = true;
}
再次執(zhí)行Update-Database：
因?yàn)槲野验L度從max改為10，在更新數(shù)據(jù)結(jié)構(gòu)時，它認(rèn)為此操作會導(dǎo)致數(shù)據(jù)丟失，如下：
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
No pending code-based migrations.
Applying automatic migration: 201212090848057_AutomaticMigration.
Automatic migration was not applied because it would result in data loss.
如果確保沒事，只需給此命令加個強(qiáng)制執(zhí)行的參數(shù)即可：
Enable-Migrations -Force
最后再次執(zhí)行：Update-Database
數(shù)據(jù)庫中的原數(shù)據(jù)也沒有丟失！