I have a service which uses EF Core runtime migrations on startup:
var migrator = dbContext.Database.GetService<IMigrator>();
await migrator.MigrateAsync("targetMigration", cancellationToken);
To generate the migrations I first update the DbContext class, then perform "dotnet ef migrations add" to generate the migration code.
It may happen that a deployed upgrade will be automatically rolled back to the previous version after a migration has occurred. For example if health checks or tests fail. In this case I want the previous version of the application to be able to automatically roll back the migration. I know MigrateAsync can revert migrations, but in my current workflow the migration code will not be in the previous version of the code, so I am not sure whether it will be able to revert the migration.
I can think of a workflow like:
Change DbContext and run "dotnet ef add migration" to generate the migration code
Revert the DbContext change and deploy the application so that the code for migration 'n' exists, but the target migration in MigrateAsync and the version of the DbContext is 'n-1'
Re-apply the DbContext change, change MigrateAsync to target migration 'n', and deploy the application
But this seems awkward and I am not sure whether it is necessary, and whether it would definitely work.
What is a good strategy for deploying code first runtime migrations using EF Core such that if the previous version is deployed, the migration can be automatically rolled back?
From what I know, EF does not have anything prepared for you case, it is really hard to make migrations back and forth in prod, also, you must consider that many migrations can create data loss.
First you need to create a process when a change must be tested very well, when the change gets to production you should be 99% sure that there wont be rollbacks in prod.
As you say, you would need the last version of the code, if not, EF wont know what "down" should do.
In our current system, we analyse each migration, if is a new table or something simple, we just run the migration from the CI. If it is something more complex, or we need more complex movements (table modifications with millions of rows), we just do it by hand, so we can send data to temp tables, fill empty data or work with special functions we just generate the script and work with it.
dotnet ef migrations script 20190725054716_Add_new_tables
It is a really hard problem, Java and JPA shares the same problem to generate a history.
These migrations generators are great for development, but hard for production, changing environments, specially when you need to go back and forth like you, another option is to use other tools to handle the migrations that are better prepared for this scenario, like liquibase
Another idea can be found here:
I ended up creating a custom tool that executed migrations
intelligently and automatically determined which model (context)
assembly to use for the migration.
The title is a bit confusing but I'm trying to specify that the problem is not initiating a code first model and migration for an existing database, but comes after that.
I needed to activate automatic migration because we switched to a code first model for our system. So, here's what has been done:
I created an empty InitialCreate for the existing database
I did some other scripts because there were some changes, those worked OK and the scripts were created and run on database
The problem happen when I want to use those script and migrate another database that was not yet initialized this way. I don't know what to do.
When I try to run Update-database I get the error:
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.
If I do a Add-Migration it creates a migration with everything in it again, all the create tables, it's like it ignores my currents scripts, the fact that there is a InitialCreate empty and the other scripts.
OK, you have 2 databases - let's say DEV and PROD. Both are in an identical state and have the same schema before migrations have been enabled. This is what to do:
1 - Add migrations to your DEV environment and set your database initializer to MigrateDatabaseToLatestVersion. Another option is to programatically run migrations.
enable-migrations
// take a snapshot of current state. -IgnoreChanges prevents recreate of existing objects.
add-migration InitialBaseline -IgnoreChanges
update-database
2 - There are several ways to keep the other database(s) in sync:
A) Maintain migrations in parallel by changing the connection string. So point at PROD, and run update-database to create the __MigrationHistory table and apply the initial, blank, baseline. I don't recommend this option for PROD databases (see below).
B) Sync with scripts. Many organizations don't want EF applying changes and instead require DBAs to apply scripts. For this option, you may want to set your database initializer to NULL. In this case you can do an update-database -Script to generate changes. This would be done on migrations subsequent to your initial baseline since they are already in sync. See here for more info on this technique.
C) Use database projects or a diff tool to keep things in sync.
Now when you go and change your models in DEV:
add-migration Changes1
update-database
For option A, change connect string and repeat. For option B, use update-database -Script. For option C, resync with tool.
NOTE: "I needed to activate automatic migrations..." - Automatic migrations are a whole different matter and can complicate the process. See here.
EF Migrations could not automatically detect some complex changes, so I created an empty migration and made changes by hand to Up() and Down().
I updated the database, and everything worked in both forward and reverse directions.
But later, when I made more changes and created a new migration, it automatically added all kinds of changes which were not needed - as I already handled them manually in the previous migration.
I know I can delete all migrations and start from scratch, but that'll create far too many problems, so I don't want to do that.
How do I fix this?
You can always establish a new baseline if you don't have prior released databases out there. Delete all the old migrations then run:
Add-Migration MyBaseline –IgnoreChanges
Update-Database
Now your model and database will be in sync and you can make model changes and create new migrations. I usually turn automigrations on until I am ready to deploy then I roll them into a single migration that I can script out to clients.
https://msdn.microsoft.com/en-us/data/dn579398.aspx#step3
Delete the offending junk from the Up() and Down() functions
Compile
Update-Database
What am I doing wrong. I have got a user DbContext setup and working when I originally created the Code-First with powershell it all worked fine.
I implemented Database Initializer as expected on application start.
Database.SetInitializer<UserDbContext>(new CreateDatabaseIfNotExists<UserDbContext>());
Just to test out if it really creates the database I actually dropped the database and now I am stuck the database will not be created. I am using SQL Server 2012, any idea what could be wrong.
The error message I am getting is
System.InvalidOperationException: Migrations is enabled for context 'UserDbContext' but the database does not exist or contains no mapped tables. Use Migrations to create the database and its tables, for example by running the 'Update-Database' command from the Package Manager Console.
I have tried the same from Package Manager console and it is still give me the same message.
Finally figured the solutions, not sure why or what. Changed my Database initializer to MigrateDatabaseToLatestVersion instead of CreateDatabaseIfNotExists worked.
Database.SetInitializer<UserDbContext>(new MigrateDatabaseToLatestVersion<UserDbContext, Configuration>());
Edit:
With your new error message the problem comes from you having migrations enabled and already ran a migration (probably the first creation of the database) and since you dropped the DB the migration history has been lost. If your not using Automatic migrations you can not go in and make changes to the database your self and expect code-first to know about it. Try disabling migrations and re-enabling them to see if that clears out the migration history.
You will need to make a call into the DB either as a read or insert of data for the DB to initially be created. The code you use only tells EF how to deal with a database if one does not exist when it tries to find it. For me I use the method outlined at http://www.codeproject.com/Tips/411288/Ensure-Your-Code-First-DB-is-Always-Initialized
We have multiple developers working on a project that uses Entity Framework 5.0. Every developer uses his own local SQL 2012 database so he can develop and test without impeding others.
At first, we used a hybrid of automatic migrations and code-based migrations. That didn't work well at all so we decided to disable automatic migrations and to only allow code-based. I should add that we started again with a clean database without a 'corrupted' _MigrationsHistory from all the automatic migrations.
So now the workflow is:
Developer changes his datamodel
Does add-migration <Name> and applies it to his database with update-database.
Checks in the datamodel change and the migration into Git.
Another developer pulls, receives the changes and applies it to his database.
So far, this worked well. However before today it was usually just me who made the migrations and the others applied them. But today there were migrations from three developers. I just pulled those migrations, did an update-database which went fine.
I also had a change to my own datamodel however so at the end of the update-database it gave me a warning that I still wasn't up to date so I did add-migration <my migration>. However when it scaffolded the migration, it gave me the changes of all the migrations I had already applied to the database. So: it tried to drop columns that had already been dropped, tried to create a table that already existed, etc.
How can that be? My assumption was that EF would just check the _MigrationsHistory table and find out which migrations weren't present in the table yet and apply those one by one ordered by the timestamp that's part of the name. But apparently not, because even when I undo my own changes and I have a clean environment it still complains my database isn't in sync with the model. But I just pulled those changes and applied them to my database. It is in sync. I can see the migrations that I just applied in the _MigrationsHistory table too.
The only thing I can think of is that I added a property to a datamodel that wouldn't result in a database change (I added a List<X> to datamodel Y where X is the many in the one-to-many relationship. This wouldn't result in a database change as X already had a foreign key to Y). Could that be it? If so, that's really fragile because there's no way to add a migration for that since there's no database change and I'm not sure how to fix this either.
I'm not sure how to deal with this, because I can of course just edit what it scaffolded and remove everything that has already been applied to my database. But then what? I check it in and then some other developer gets the same message that his database isn't up to date even after applying my new changes, scaffolds his own changes, gets the same nonsense scaffolding, edits it, checks it in and then the next developer gets it. It becomes a vicious circle and a similar one to what we had when we used automatic migrations and I thought we had fixed that by switching to code-based only. I can't trust it right now to do the right thing and it's a nightmare to work with like this.
What I also tried is adding the migrations I pulled from my coworkers one by one with update-database -t:201211091112102_<migrationname> but to no avail. It still gives me the erroneous scaffold.
So what did we do wrong here, or is EF simply not built for collaboration like this?
UPDATE
I created a reproducible test case, it's a bit of a lengthy dance though in order to simulate this multi user/multi database scenario.
https://github.com/JulianR/EfMigrationsTest/
Steps to reproduce when you have the above project (these steps are also present in the code):
add-migration Init
update-database (on database 'TestDb')
Change connection string to point to TestDb1
update-database on TestDb1
Uncomment property Foo on class Test
add-migration M1 to add property Foo to TestDb1
Comment out Test.Foo again
Change connection string to point to TestDb2
Exclude migration M1 from project so it doesn't get applied to TestDb2
Uncomment property Bar on class Test
update-database to apply Init migration to TestDb2
add-migration M2 to add property Bar to TestDb2
Change connection string to point to the original TestDb again
Include migration M1 into the project again
Uncomment property Foo on class Test
Uncomment property SomeInt on class Test
update-database
add-migration M3
update-database, get an error because M3 tries to add column Foo to database TestDb which was already just added by migration M1.
The above is to simulate three users, where user 1 inits his database, the other two use his initialization to create their database as well. Then user 2 and user 3 both make their own change to the datamodel and add it to source control together with the migrations needed to apply the changes. Then user 1 pulls the changes of user 2 and 3 while user 1 has also made a change to the database himself. Then user 1 calls update-database to apply the changes of user 2 and 3. He then scaffolds his own migration which then erroneously adds a change from user 2 or 3 to the scaffolded migration which causes an error when applied to user 1's database.
You need to add a blank "merge" migration that will reset the snapshot of the latest migration in the .resx file. Do this using the IgnoreChanges switch:
Add-Migration <migration name> -IgnoreChanges
See here for an explanation
You need to manually resolve migration conflicts just like you would code conflicts. If you update and there are new migrations, you need to ensure that the metadata behind the last migration matches the current model. To update the metadata of the migration, re-issue the Add-Migration command for it.
For example, before step 17 (Update-Database) in your scenario, you should issue the following command
Add-Migration M2
This will update the metadata to bring it in sync with your current model. Now when you try and add M3, it should be blank since you have not made any further model changes.
Option 1: Add a blank ‘merge’ migration
Ensure any pending model changes in your local code base have been
written to a migration. This step ensures you don’t miss any
legitimate changes when it comes time to generate the blank
migration.
Sync with source control.
Run Update-Database to apply
any new migrations that other developers have checked in. **
Note:****if you don’t get any warnings from the Update-Database
command then there were no new migrations from other developers and
there is no need to perform any further merging.
Run Add-Migration
–IgnoreChanges (e.g. Add-Migration Merge
–IgnoreChanges). This generates a migration with all the metadata
(including a snapshot of the current model) but will ignore any
changes it detects when comparing the current model to the snapshot
in the last migrations (meaning you get a blank Up and Down method).
Continue developing, or submit to source control (after running your
unit tests of course).
Option 2: Update the model snapshot in the last migration
Ensure any pending model changes in your local code base have been
written to a migration. This step ensures you don’t miss any
legitimate changes when it comes time to generate the blank
migration.
Sync with the source control.
Run Update-Database to
apply any new migrations that other developers have checked in. **
Note:****if you don’t get any warnings from the Update-Database
command then there were no new migrations from other developers and
there is no need to perform any further merging.
Run Update-Database
–TargetMigration (in the example we’ve been
following this would be Update-Database –TargetMigration AddRating).
This roles the database back to the state of the second last
migration – effectively ‘un-applying’ the last migration from the
database. ** Note:****This step is required to make it safe to edit
the metadata of the migration since the metadata is also stored in
the __MigrationsHistoryTable of the database. This is why you should
only use this option if the last migration is only in your local
code base. If other databases had the last migration applied you
would also have to roll them back and re-apply the last migration to
update the metadata.
Run Add-Migration
(in the example
we’ve been following this would be something like Add-Migration
201311062215252_AddReaders). ** Note:****You need to include the
timestamp so that migrations knows you want to edit the existing
migration rather than scaffolding a new one. This will update the
metadata for the last migration to match the current model. You’ll
get the following warning when the command completes, but that’s
exactly what you want. “Only the Designer Code for migration
'201311062215252_AddReaders' was re-scaffolded. To re-scaffold the
entire migration, use the -Force parameter.”
Run Update-Database to
re-apply the latest migration with the updated metadata.
Continue
developing, or submit to source control (after running your unit
tests of course).
MSDN have a great article on this. Please go through it.
Entity Framework Code First Migrations in Team Environments
We are having similar issues in our environment, here is what we've figured out so far and how we got around it:
When you have changes that you have applied (update-database) but not checked in, and then you receive changes from another developer who doesn't have your changes, this is where things seem to get out of sync. In our experience, it seems like the meta data that is saved for your own changes get over written by the meta-data from the other developer when you do the update-database process. The other developer doesn't have your changes, so the meta-data that gets saved is no longer a real reflection of your database. When EF does a comparison after that, it 'thinks' that your changes are actually new again because of the meta data change.
A simple, admittedly ugly workaround is to do another migration, and wipe out it's contents so you have empty up() and empty down() methods. Apply that migration and check it into source control and let everyone sync to that. This simply syncs up all of the meta data so everyone has all of the changes accounted for.
I have added an issue on codeplex, this issue causes many a head scratching in our team too.
The link is https://entityframework.codeplex.com/workitem/1670
I have put some thought into this and I hope I will contribute to the different opinions and practices presented here.
Consider what your local migrations actually represent. When working locally with a dev database, I use migrations to update the database in the most convenient way possible when adding columns etc to tables, adding new entities etc.
So, Add-Migration checks my current model (let's call it model b) against my previous model (model a) and generates a migration to go from a => b in the database.
To me it makes very little sense to try and merge my migrations with anyone elses migrations, if everyone indeed has their own database and there then exists some kind of stage / test / dev / production database servers in the organization. This all depends on how the team has it set up, but it makes sense to insulate each other from changes that other people make if you want to truly work in a distributed manner.
Well, if you work distributed and have some entity, Person, for example, that you work on. For some reason, lots of other people are also working on it. So, you add and remove properties on Person as needed for your particular story in the sprint (we're all working agile here, aren't we?), like Social Security number that you first made into an integer because you aren't that bright and then to a string etc.
You add FirstName And LastName.
You are then done and you have ten weird up and down migrations (you probably removed some of them while working since they were just crap) and you fetch some changes from the central Git repo. Wow. Your colleague Bob also needed some names, maybe you should've talked to each other?
Anyways, he has added NameFirst and NameLast, I guess... so what do you do? Well, you merge, refactor, change so it has more sane names... like FirstName and LastName, you run your tests and check his code, and then you push to the central.
But what about the migrations? Well, now would be the time to make a migration moving the central repo, or the branch "test" more specifically, contain a nice little migration from its model a => model b. This migration will be one and only one migration, not ten weird ones.
Do you see what I'm getting at? We are working with nice little pocos and the comparisons of them constitute the actual migrations. So, we shouldn't merge migrations at all, in my opinion, we should have migrations-per-branch or something like that.
In fact, do we even need to create the migration in the branch after merge? Yes, if this database is updated automatically, we need to.
Another thing to consider is to never actually creating a migration before doing a pull from the central repo. That means you will both get the other team members' migration code and their changes to the model before creating your migration.
Gotta work some more, those are my thoughts on this, at least.
The solution I was able to come up with (at least for 2 users, haven't tested for 3) is:
merging migrations to sync up the meta-data run update-database (this should fail), then
add-database and then
delete all of the generated code in up() and down() methods
this will still be run by update database but won't do anything, just bringing the metadata up to sync.
I agree with #LavaEater. The core of the issue, it would seem, is that migration scaffolding should be centralised. Perhaps as part of some automated/integrated build process each time a push occurs? Thereafter the resulting migrations can be pulled from the server by team-members.
This means that their own migration scripts should not be pushed to the server.
There is an easy way to have no merge conflicts/errors with migrations.
Work on your branch as you would do at any time.
If you merge to master and have merge errors then:
remove all *.cs files from migrations folder.
do git checkout master ./* inside migrations folder.
Recreate your migration.
Your snapshot is up2date and there is no merge conflict.
Also just before merging pull request to master you need to merge with master and do steps 3-6 ALWAYS.
Below is simple Powershell script that does steps 3-6:
function Write-Info($text)
{
Write-Color "$pwd", "> ", "$text" -Colour "Yellow", "Blue", "White"
}
function Create-Migration($project, $migrationName, $referenceBranch)
{
Set-Location "$SolutionPath\$project"
Write-Info "Going to migrations"
Set-Location "Migrations"
Write-Info "Removing ./*.cs"
Remove-Item ./*.cs
Write-Info "git fetch --all"
git fetch --all
Write-Info "git checkout origin/$referenceBranch ./*"
git checkout origin/$referenceBranch ./*
Set-Location ..
Write-Info "Creating migration $migrationName "
dotnet ef migrations add "$migrationName"
}
I am working with that method for last half year. 0 merge conflicts to resolve when it comes to migrations 8).