Using Entity Framework 5, we're using Code-First Migrations in our application. Every developer has his own database on which they work.
I have accidently emptied mine: There is nothing in there anymore, no tables, not even the migration history table.
So, I've tried to update the database again through the PM console by executing update-database. It immediatley gives me an error that a table does not exist, while it should be created in my inital code migration.
What is interesting is that the PM console also shows what migrations are being applied, which does not contain the inital create code migration, thus not creating any tables at all, and ofcourse failing at later migrations.
I tried executing update-database -targetmigration:initialcreate which gives me the message that that code migration does not exist, while it is a direct copy/paste from the cs file, so the id must be correct (note: this works for other migrations).
I also tried update-database -targetmigration:0 and update-database -targetmigration: $InitialDatabase which both give me 'Target database is already at version 0'.
I've also tried deleting the database altogether and let EF create it for, didnt work either, it keeps skipping the initialcreate migration.
So how do I get Code Migrations to execute my initalCreate code migration?
Working with EF migrations in a team scenario is not ideal to say the least. The best practice my team follows is to never commit migrations. Migrations are personal and apply only to your particular database instance. If everyone commits their own migrations you end up with a mess, quick.
While not directly related to your question, some may wonder how you deal with production migrations. Simply, you don't. Your Release Manager, or whoever will actually push the release live, should generate SQL to apply all the changes at once, and then hand this off to your DBA, or whoever manages the production database.
That said, in the scenario that you describe, where you database has been emptied. The best fix is to delete all migrations in your Migrations folder. Even and especially, the initial migration (they don't matter, anyways, because you shouldn't be holding on to them outside of your personal codebase). Then generate a new migration, which will trigger EF to compare your current database state (empty) with the state of the app and essentially create a new initial migration based on the current state of your app. Then, you can apply this migration.
Related
I have gotten myself into an odd Groundhog Day scenario with an MVC application of mine.
Unless I apply my workaround (Later in this question) each time I debug the application I'm presented with this error:
The model backing the 'UsersContext' context has changed since the
database was created. Consider using Code First Migrations to update
the database (http://go.microsoft.com/fwlink/?LinkId=238269).
I have not changed the model.
My workaround workflow is:
Add-Migration WHATEVERNAME (Makes a blank migration)
Delete this migration.
Run: Update-Database
Recompile & Run (Now without error)
Notes:
The __MigrationHistory hashes of the latest migration match in both script and in the database.
I have my MVC application & EF project as separate projects.
I have tried creating an -IgnoreChanges migration, to see if applying this would mitigate the issue. It did not.
This is quite frustrating, how would I solve this issue permanently?
Note: Automatic migrations are not suitable for my scenario.
Well, it's almost impossible to understand what's wrong without knowing much more detail. So all I can do is give you some clues of what you could try.
Stopping and restarting the app should not cause the DB to get out of date. Is it only when debugging? Have you tried running the app without debugging? Then recycle the app pool and running the app again.
Do you have any weird post-build step that will overwrite some DLL in your "bin" folder?
Is your app doing something that changes the database schema, thereby invalidating it when you next start up? Run SQL profiler to check what is happening to the DB when your app starts up.
Migrate back to the first version of your schema, and then back again (backup your DB first):
update-database -TargetMigration:0 -verbose
then
update-database -verbose
Temporarily comment out the bulk of your app to try to isolate the cause.
Create a brand new app with EF configured in the same way, copy the connection string and see if it happens for that. If not, then there must be something different. If yes, then show us your EF settings.
Hopefully something here that could give you an idea at least. Good luck!
Enabling migrations sets up the whole migration system. But to enable automatic migrations you have to include -EnableAutomaticMigrations which simply adds the line
AutomaticMigrationsEnabled = true;
into the newly generated Configurations.cs file.
In conjunction with the database initializer, development turnaround is more streamlined because you no longer have to type add-migration and update-database every time you make a change. That will happen automatically now. However, that’s not enough, if you want column removals you have to also perform step 3, where automatic data loss is supported.
When you are ready to release software (internally or externally) where you need strict version control and to upgrade databases on site, you should remove automatic migrations and add a manual migration point.
This can happen when updating to EF6 which made schema changes to the _MigrationHistory table (https://msdn.microsoft.com/en-us/data/jj591621)
The EF6 version has a new column ContextKey so the migration is probably trying to add that column.
I'm guessing if you scaffold it will just be making those changes - or perhaps there's something you changed a long time ago that wasn't 'picked up' yet for some reason.
OR if you just don't want to deal with it right now you can disable migrations temporarily.
System.Data.Entity.Database.SetInitializer<UsersContext>(null);
I am using EF code first and asp.net MVC. Here is my technical stack.
Visual Studio 2010
Entity Framework 4.3.1
In my migrations folder, I can see three migrations files are existing.
InitialCreate
AddStandardException
DocumentScope
When I check my database I can see that _MigrationHistory table has all three migrations applied. Now I have added one more DbSet, and I want to write migrations for it. When I attempt to give this command
Add-Migration NewTable
It gives me this error :
Unable to generate an explicit migration because the following explicit migrations are pending: [201402121621095_AddStandardException, 201402190713571_DocumentScope]. Apply the pending explicit migrations before attempting to generate a new explicit migration.
I don't understand why is it complaining about pending migrations whereas all migrations have been applied?
How do I even troubleshoot this ? I tried with -Debug switch but no luck.
I found a workaround to it. I have just commented code inside the Up() and Down() functions. Then ran Update-Database. It applied some dummy migrations and then reported that
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.
After this when i ran
Add-Migration NewTable
It gave me the correct result. Any idea whats going on here ?
You either need to run "update-database" from the package manager console to push your changes to the database OR you can delete the pending migration file ([201402121621095_AddStandardException]) from your Migrations folder and then re-run "add-migration" to create a brand new migration based off of your edits.
Explanation: "update-database" basically modifies existing table fields while "add-migration" works like git by making a snapshot of the distinct model changes. These snapshots show how the database evolved over time so they are more useful to your code user than the EF or the App itself.
That being said, it is possible that your newer classes have a quite different code signature which may not "flow" with the existing classes.
Solution: Modify or remove the previous migrations since the new migration will create a new data structure that won't use or need them
I have been developing my app in a code-first approach atop an exisiting database.
Only now do I have a need to run a migration. I don't want to destroy this database when my model changes because it is very large and it has nice sample data in it.
How can I run a migration without the framework telling me that there are pending changes to apply? (The code runs anyway as I do my migrations from Rails-tho I would like to do them from here)
I do not want to set up automatic migrations because I am working on a big database with lots of seeded data that I do not want to delete/recreate. I also want to have control over what is made, deleteded and when.
This is also needed for when I take it to production, I'd like to roll out the changes via Migration instead of manually. How can I migrate by adding in/removing the fields I want and not have EF care about what it is I do?
If I know how it knows which one it is on (like Rails) can I trick her into thinking that she can run the migrations I want?
I thought that setting the initializer by:
Database.SetInitializer<MyDbContext>(new CreateDatabaseIfNotExists<MyDbContext>
would take acre of it, but it does not.
To answer the question in the title, because there's a sys table __MigrationHistory which tells EF that there is a difference in your tables vs what the database has.
As far as how to do it (from package manager console):
Enable-Migrations
In the configuration class set AutomaticMigrations = false;
Set your Database.SetInitializer<Context>(null) so it doesn't DropCreate or Update
AddMigration <name> to queue any pending changes to a change model
Update-Database will call the MigrationName.Up method to alter the database with any changes (sans losing data).
There's a Table "__MigrationHistory" that EF uses to store Migration Name / Order. You can backup this table in your dev environment, then delete these records. When you deploy to production, you run the migrations. Another option is use Database compare (dev / prod) and get scripts to change your tables / data.
I have a MVC 3 project were I use code based migrations together mith automatic migrations(this works).
When I install this project on a new server the database is created by CreateDatabaseIfNotExist initializer, cause I´m using the seed method of this. After executing this I have a __MigrationHistory table with one entry. The model hash of this entry is exactly the same like the last one from my developement server. On my development server I have an entry for each of my code based migration in the __MigrationHistory table.
Now the problem is that when I try to run the migrations on the new server, I expected them to say to me "nothing to do, cause model hash is same", but instead of this the migrations seems to look only for the MigrationId in the database and try to execute every migration whose MigrationId is missing. Of course this leads to Exceptions, cause the migration tries to add database structures already there.
I think this should be a very common scenario, so is there a kind of workaround for this? My workaround for the moment is to copy all contents from the __MigrationHistory of the development system to the new server, but this is very tricky, due to the dealing with the modelhash as varbinary. Is there a better solution or did I understand some logical things wrong?
I just installed Entity Framework Migrations, added a property to a class, and gave EF Migrations a whirl.
My development database was promptly updated. So far, so good.
Now, I want to create a change script for this initial use of Migrations for the production database. Note there was a pre-existing database because I applied this to an existing project.
The migrations I have are:
PM> Get-Migrations
Retrieving migrations that have been applied to the target database.
201204102238194_AutomaticMigration
201203310233324_InitialCreate
PM>
I thought I could get a delta script using the following:
Update-Database -SourceMigration:201203310233324_InitialCreate -TargetMigration:201204102238194_AutomaticMigration -script
However, that gives me the error:
'201204102238194_AutomaticMigration' is not a valid migration.
Explicit migrations must be used for both source and target when
scripting the upgrade between them.
Just to see what would happen, I reversed the two parameters (backward migration) and did get the script I would expect after adding the -force flag (new columns dropped).
How can I get a script for this first migration?
The right way to start using EF migrations with an existing database is to start with adding an empty migration that contains the metadata of the current database.
I think that you have to roll back to a model that is compatible with the initial database schema. Then run the following command:
add-migration InitialSchema -IgnoreChanges
That should give you an initial migration, that does nothing, but contains the metadata of the current model. You can of course add migrations later with -IgnoreChanges if you've expanded your code model to cover more of the tables already present in the database.
Once you have that initial migration step in place, the scripting would work.
Generally I would not recommend to use automatic migrations unless you only ever intend to only use automatic migrations. If you want some kind of control over the changes to the database (including scripting them) then code-based migrations is the way.