如何在Entity Framework代码优先中将列更改为唯一身份

Question

I have redesigned my class scheme many times since started the project I'm working on.

At first I didn't know about data annotations, so I have migration1 , where my Ids have no DatabaseGenerated.Identity option and migration4 where they already have it.

Turns out that EF doesn't work this way ( https://entityframework.codeplex.com/workitem/509 as for EF5), so when I added some seed data, it threw an exception

Cannot insert the value NULL into column 'primarykeycolumn', table 'tablename'; column does not allow nulls. INSERT fails.

What's really interesting is when I deleted all existing migrations and scaffolded new one from scratch, seed method ran without any problems.

So I have a question: do I need to do it any time I make changes to scheme such as adding data annotations like Identity or is there a way to save my previous migrations? Because dropping and recreating db in real-life can result in a huge data loss, which I want to avoid.

Answer 1

Adding Migrations. In your Package Manager Console

Add-Migration Test1

In your Configuration.cs from Migration Class You will see Up method and Down Method. It is like Before, and After Changes. You can call them up if you want to reverse the Changes.

doing Add-Migration "NameoftheMigration" does not implement it

you need to call

Update-Database

If it tells you that there is an error, or potential Data lost.

Update-Database -Force

If you choose to use CodeFirst. You can't really Jump from Altering table by Design, then by code. You have to Choose one. As CodeFirst Migration rely on Models. Data First, Rely on Data Design.