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.
We have large number (about 735) of migrations in our project. In some of them, we have made manual changes. How we can convert them to single file or decrease the number of them? We cant remove migrations and add a new migration to make them a single file, because we will lose manual changes that we do in migrations.
(we cant remove migrations and Add a new migration for make them to a single file ,because we will lost manual changes that we do in migrations).
That is the method. You shouldn't be making manual changes to the migrations, in the first place, and this is one reason why. You either go code-first, and generate migrations from your code (only) or you go database-first, and scaffold the code based on the database. You're trying to do some hybrid, where you're making changes to the database that aren't being reflected in your code, and that's bad design.
I am new to Entity Framework 6 Code First and am trying to perform what I thought would be a simple task. I want to create a SQL View and then have an Entity in my database context that I can use to query the view.
I have tried articles such as this but the key difference in my case is that the SQL View is not an existing view coming from another existing database.
I examined the proposition made in this article but it seems like overkill to me that I would need to create some extension methods to do something as simple as create a view/entity combo and use it in my database context.
Am I missing something? I know it would be much easier if I weren't using Code First but please keep in mind it's Code First and I am trying to create a view, not reuse one from an existing database.
Colin and Kevin, Thank you for the link to your answer on the other post and your concise answer. I have used several resources to finally create a queryable entity based on a new SQL view. Just in case anyone else is new to EF 6.0 Code First and is just getting their feet wet, I do have a few steps that will hopefully benefit others in the future.
It may seem obvious to more seasoned Entity Framework developers, but in order to execute the 'Migration' approach you need to disable automatic migrations and actually dive into the guts of the Code First Migrations inner workings. Since automatic migrations is turned on out of the box, I had already created a fairly complex database with seed scripts all relying on automatic migrations and rebuilding the database on every run of my application. This post helped me wipe my migrations history and get to square 1 with automatic migrations turned off (I went with the web.config approach in case you were wondering)
After I had cleared my migrations information, I deleted the mdf from within solution explorer. That guaranteed that I wouldn't run into any problems when running Update-Database (further down the list of steps).
In the Package Manger console, I then executed Add-Migration Initial to generate an "Initial" migration. The result of this was the editable Up and Down methods as described in Colin's answer. I then followed the steps in Colin's answer by commenting out the table create statement (Entity Framework tries to create a table but we really want to create a view and map it to the Entity) and inserting my own view create sql statement at the end of the Up method. It's important to put the create statement after the creation of any tables that it may depend on. I also performed my Seed activities in the Configuration.Seed method instead of in my Context's Seed method. I see how this would be important if you were dealing with multiple migrations. Finally, as Colin suggested I added the table mapping to my context's OnModelCreating event.
The final step in this was to actually apply the migration to the database. In order to do that, in the Package Manager console you execute the Update-Database command. That statement will rebuild the database with the "Initial" migration you created and edited in earlier steps.
It still surprises me that I need to do all of this custom work to create a view and map it to an entity with Code First, but at the end of the day it was helpful in getting me started on migrations as you can only rely on the "automatic migrations" for so long anyways.
You can manually add the sql to create the view to a migration then consume it as per your first link.
The answer in the link provided by Colin does the job.
In case there are lots of views to be created, it can be a good idea to save the view queries in separate files and add them in a resource (.resx) file instead of hard-coding the sql queries in the Migration Up() method.
For e.g.
public override void Up()
{
Sql("ResourceFileName.ResourceName");
}
instead of hard coding like
{
Sql("EXEC ('CREATE View [dbo].[ClientStatistics] AS --etc");
}
I'm learning to use EF Code First Migrations from https://msdn.microsoft.com/en-us/data/jj591621.aspx
Somewhere it said:
Code First Migrations has two primary commands that you are going to
become familiar with.
Add-Migration will scaffold the next migration based on changes you
have made to your model since the last migration was created.
Update-Database will apply any pending migrations to the database.
I don't understand what's Add-Migration doing exactly. To more precise, my problem is with:
since the last migration was created
In order to create a migration, it should pick two database structure to compare.
Obviously, one side is the current structure of models in the code. But what is the other side? The options are:
Populating a database structure by unifying all migrations from initial to the last migration before this?
Comparing it to a database which has the old structure?
Check the code behind files of your migrations - they contain a lot of metadata, including a snapshot of the model from when it was created.
So, when you run Add-Migration the process is approximately this:
Build a model based on your code
Find the previous model from your last migration (if applicable)
Compare the two models
Generate a migration based on the difference
There's a useful article with some information and videos that cover this in more detail.
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).