Do I use Snapshot file, migration file or data annotations in my EF Core to update database? entity-framework-core


I'm trying to understand the different types of migration paths we can choose when developing an ASP.NET Core 1.0 application with EF Core. When I created my first Core application I noticed it generated a ApplicationDbContextModelSnapshot class that uses a ModelBuilder to build the model.

Then I read that if I need to add a table to the database, I need to create the new model and run the command line to generate the migration file and update the database. Ok, I get it up to this point.

But when I do that, I notice that the ApplicationDbContextModelSnapshot class gets updated too.

1) Does that mean I cannot modify this ApplicationDbContextModelSnapshot class since it looks like it gets regenerated each time?

2) Should I use Data Annotations to build my model or should I use Fluent API which tells me to build my model in the ApplicationDbContext class? Huh? another file that builds the model?

I'm seeing three different ways of working with the database here, the snapshot class, data annotations, and fluent API. I'm confused because today, I made a mistake in my last migration file so I deleted the file, dropped the database and reran the database update.

But by doing that I got errors similar to:

The index 'IX_Transaction_GiftCardId' is dependent on column 'GiftCardId'.
ALTER TABLE ALTER COLUMN GiftCardId failed because one or more objects access this column.

So naturally I was wondering if I had to modify the ApplicationDbContextModelSnapshot class.

What is the path I should be taking when it comes to migrations or database updates because these three paths are confusing me.

9/19/2016 7:10:30 PM

Popular Answer

I have run into this issue before when I create migrations, make model changes, create new migrations, and try to update the database. The root cause is when keys are being changed and relationships are not dropped and are not added back or do not exist.

You have two options

Easy Method The easiest way is also the most destructive way and only possible in a dev environment.

Delete all migrations, drop the database, create new migrations and run 'update-database'.

Hard/Safest Method This is the most time consuming method. I recommend do this in a local integration branch first, pushing it to a remote integration, and then production.

Open the migration file, ie 20160914173357_MyNewMigration.cs. Drop all indexes in order Drop/Add/Edit table schemas Add all indexes back.

For either method, just be sure to test and test again.

9/20/2016 12:37:27 AM

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