PM> enable-migrations
Checking if the context targets an existing database...
Code First Migrations enabled for project BTCheck.PM> add-migration init
Scaffolding migration 'init'.
The Designer Code for this migration file includes a snapshot of your current Code First model. This snapshot is used to calculate the changes to your model when you scaffold the next migration. If you make additional changes to your model that you want to include in this migration, then you can re-scaffold it by running 'Add-Migration init' again.PM> update-database
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
No pending explicit migrations.
Unable to update database to match the current model because there are pending changes and automatic migration is disabled. Either write the pending model changes to a code-based migration or enable automatic migration. Set DbMigrationsConfiguration.AutomaticMigrationsEnabled to true to enable automatic migration.
You can use the Add-Migration command to write the pending model changes to a code-based migration.按照正常的codefirst的執行順序，代碼也沒有問題，但就是無法更新到數據庫。
原因在於在更新數據庫之前沒有生成解決方案，只要build一下再次update-database一下就可以了。
PM> update-database
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
Applying explicit migrations: [201711101328231_init].
Applying explicit migration: 201711101328231_init.
Running Seed method.