Azure移动服务和EF Code First-上下文已更改错误

Question

I have an Azure mobile service backed by a SQL database. I've been happily deploying to this for weeks and manage my DB using EF Code First. Now though, I've hit a brick wall whereby any request to the mobile service breaks with an error:

The model backing the '[yourcontext]' context has changed since the database was created.

The thing is though, it hasn't! I've tried the following:

1.  Re-depoyed the service *several* times
2.  Run ‘Add-Migration’ to see if it mystically picks up any new fields/properties
3.  Run ‘Update-database’ which runs without any issues
4.  Combinations of 2&3 over and over
5.  Deleted the Migration History table
6.  Deleted ALL tables from my DB and re-run update-database, which again completes without error
7.  6 then 3, which recreates the database

Any ideas how I can resolve this insantiy?

Answer 1

AFAIK, the Code First Migrations can be executed manually or automatically. I would prefer to choose the automatic migration. You could add the following code to App_Start\\Startup.MobileApp.cs file for enabling automatic migration as follows:

Database.SetInitializer(new MigrateDatabaseToLatestVersion<Models.MobileServiceContext, Migrations.Configuration>());

Or

var migrator = new DbMigrator(new Migrations.Configuration());
migrator.Update();

Note: You need to either configure AutomaticMigrationsEnabled to true under Migrations\\Configuration.cs without manually adding pending model changes to a code-based migration via Add-Migration or you could just use Add-Migration for adding pending model changes without set AutomaticMigrationsEnabled to true.

Based on your issue, I would recommend you changing the database name and use a new database to narrow this issue, also you need to remove the old migration files under the Migrations folder. Additionally, you could refer to adrian hall's book about Implementing Code First Migrations .

Answer 2

So I fixed it rather frustratingly by:

1. Exporting all my data out to a query window and saving the results to my local PC.
2. Renaming the old DB
3. Setting AutomaticMigrationsEnabled = true; and re-deploying
4. Letting the migration create the database (but this didnt create the table)
5. Setting AutomaticMigrationDataLossAllowed = true; #PanicModeOn
6. Re-deploying
7. Re-importing all my data

What a farce. Obviously I can accommodate this now but when my app goes into production this would be a MAJOR issue!