I am using MVC 5 and EF 6 with Code First. I got this error every time I tried to log in:
The model backing the 'ApplicationDbContext' context has changed since
the database was created. Consider using Code First Migrations to
update the database (http://go.microsoft.com/fwlink/?LinkId=238269).
This program is ok for 2 years in development until this strange error come this week. Normally after we change the model, we just simply update-database and everything ok. Today we try to do the same and no error returned :
PM> update-database
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
No pending explicit migrations.
Applying automatic migration: 202012212240459_AutomaticMigration.
Running Seed method.
PM>
We are using automated migration. But i just try to add migration manually and update-database again successfully but still returning same error.
We tried to remove the database and recreate again using update-database and a new database created, create a dummy account but still returning the same error. Tried following and checking some suggestions in other threads and still not get a good result. Deleting migration history solved the error but when we update-database for future update it will create a duplicate error, so this is not counted as a solution. I don't know what to debug anymore and what to check. Any help is appreciated. Thank you.
I think; you change your entity class,
1 - Check your entites
2 - Check your DbSet in Context class
4 Check you entity frame work version
3- remove last migration and re install
I've been recently digging into how EF migrations work and I've encountered an issue I could not really understand.
I was reading this article and here's what I saw:
At this stage Developer #2 can run Update-Database which will detect
the new AddRating migration (which hasn’t been applied to Developer
2’s database) and apply it. Now the Rating column is added to the Blogs table and the database is in sync with the model.
What I can't get is how EF determines that it has to apply the changes from the AddRatings migration. As far as I know, the workflow is as follows:
Suppose we have two migrations (with the ids 4 and 5) in the project which have not been applied to the db (say, we got the old version of the db with 1, 2 and 3 migrations applied).
Update Db command is run.
EF goes to the db, looks up the MigrationHistory table and gets the latest migration. Then, EF sees that there are migrations 4 and 5 in the project and since the latest migration in the db is 3, it applies 4 and 5.
However, when I look at the screen from the article, I don't really get it. Here's how I would expect it to go:
There are migrations First, AddUrl and AddReaders in the Dev 2 database.
EF looks up the latest migration in the db - it's the AddReaders.
The latest migration in the project is also AddReaders.
Therefore, no changes have to be applied at all.
There's an issue that the code model and the latest migration model are not the same, but EF is able to apply changes to the db anyway, though producing a warning, as the article says.
The question is, what have I got wrong in my reasoning and how EF understands that even though the latest migration in the db and code is the same, there's another migration that has to be applied.
Also, as far as I've understood, the compressed model in the MigrationHistory serves only when the Add-Migration command is run and has nothing to do with the Update-Database command. Is it so?
When performing an update EF compares the set of migrations from the assembly with the set of migrations from the database and applies to the DB all missing migrations. It doesn't matter whether the missing migrations are at the end of history list or somewhere in the middle.
Migrations are compared by MigrationId so you are right, the compressed model has nothing to do with the Update_Database command.
I'm trying to create a DbContext specific to may Domain that has one model class entirely managed by EF, and another that gets mapped to a database view. To ensure EF doesn't try to create this view that already exists, I added just the view to my DbContext and ran the following command:
Add-Migration InitialUnmanaged -IngoreChanges
This creates a Migration with an empty Up and Down, which is exactly what I want. I'm able to update my dev database using this Migration, but whenever I try to add a second Migration that includes my EF-managed model class, I get an error.
Add-Migration Initial
Unable to generate an explicit migration because the following explicit migrations are pending: [201510151553565_InitialUnmanaged]. Apply the pending explicit migrations before attempting to generate a new explicit migration.
The thing is, I've already applied that explicit Migration, and I can see it in my MigrationHistory table.
MigrationId
201510151553565_InitialUnmanaged
Can anyone help me understand why this is happening and how to work around it?
I figured this out.
When I applied the Migration, it put the Migration History table in the same default schema as the model. However, when I tried to roll it back, it was looking for the Migration History in the connected user's schema. Since it wasn't there, it thought the database was at version 0.
I created an OracleDbConfiguration class to specify a custom HistoryContext that specifies the default schema for the Migration History table and I'm able to rollback as expected after applying a Migration.
I verified that I was able to recreate my initial steps and have them work as expected now that I'm explicitly specifying the schema for the Migration History table.
Either delete the migration or just run Update-Database to put entity back in sync. If it is an empty migration your database will not change.
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).