I use Entity Framework Code First Migrations. In my project are already a lot of migrations but not the initial one. I have a dev database with an entry of the initial migration.
My question is, is there a way to recreate the initial migration cs-file to for example create another dev database.
You can force migrations to create your database from scratch:
Update-Database -SourceMigration $InitialDatabase
This will cause all database objects to be created and the migrations to be applied. See here.
Another way to do this is with initializers. You could temporarily change it to use say CreateDatabaseIfNotExists. What we do is test for the DEV environment via a web.config setting and use that initializer in DEV otherwise use MigrateDatabaseToLatestVersion or NullDatabaseInitializer in PROD.
Related
I'm migrating an API from .NET Framework 4.7 to .NET 6 (including EF to EF Core) and when I create the dbContext and execute the Add-Migration command, it creates the whole structure of the database, which I'm scared of running because I'm not sure what could change.
Is this behaviour normal? Is there any way to avoid this "initial migration" or check beforehand if this migration causes any issue on the database?
Thanks.
That's correct behaviour, EF Core migrations should be able to create full DB schema when called on an empty DB, so Add-Migration generate initial migration which will do exactly so (all existing EF4.7 migration won't be available for your EFCore 6 program).
At the same time, that initial migration will fail on existing DB because it already has all tables/columns/views.
Solution here is following: add code to the beginning of migration which checks whether one of the tables already exists:
If yes, than DB structure is already match initial migration, nothing to do here (just exist)
If not, this is blank DB and initial EFCore migration should be ran.
Here how check table existence inside migration: https://entityframeworkcore.com/knowledge-base/53473747/check-if-a-table-exists-using-ef-core-2-1
Let's say I have a database which is created by three migrations. They can be seen in the table dbo._EFMigrationsHistory and the content could look like this:
MigrationId ProductVersion
20200516181941_InitialMigration 3.1.4
20200517091058_AddedIndexes 3.1.4
20200605115456_IntroducedBreweries 3.1.4
Now let's say that I for some reason lose all of the table (or just a part of it). So suddenly the table look like this:
MigrationId ProductVersion
20200517091058_AddedIndexes 3.1.4
20200605115456_IntroducedBreweries 3.1.4
And then I make a new migration, because i changed something in the database
Add-Migration SomethingChanged
This will work fine, since we aren't talking to the database at this point. But if I try to update the database, like this
Update-Database
It will fail, because it it trying to re-run the InitialMigration (or at least so I assume). So a common error is that the tables created in the InitialMigration cannot be created, because they already exist.
During development you can simply nuke the database and/or migrations, but that's not a very viable strategy for production. It can also be done with Script-Migration, which has a from/to option, allowing something like this:
Script-Migration 20200517091058_AddedIndexes 20200605115456_IntroducedBreweries
But this doesn't seem to work on Update-Database (not in the documentation either).
Is there any (production safe) way to fix this, so that the migration history isn't broken for all eternity?
The best way I can think of, is to manually insert the missing row(s) in the database, but this seems quite hack-ish...
The Issue: You have mucked up your migrations and you would like to reset it without deleting your existing tables.
The Problem: You can't reset migrations with existing tables in the database as EF wants to create the tables from scratch.
What to do:
Delete existing migrations from Migrations_History table.
Delete existing migrations from the Migrations Folder.
Run add-migration Reset. This will create a migration in your
Migration folder that includes creating the tables (but it will not
run it so it will not error out.)
You now need to create the initial row in the MigrationHistory table
so EF has a snapshot of the current state. EF will do this if you
apply a migration. However, you can't apply the migration that you
just made as the tables already exist in your database. So go into
the Migration and comment out all the code inside the "Up" method.
Now run update-database. It will apply the Migration (while not
actually changing the database) and create a snapshot row in
MigrationHistory.
You have now reset your migrations and may continue with normal migrations.
I am relatively new to this. I am trying to publish my asp.net web application to a production IIS server. In visual studio I select Filesystem based Publishing, since web deploy is not supported by that server.
I use Code First Migrations for my Databases. As long as it is the first time, or if I drop all my tables, the deployments to production work fine. However if I have existing tables with production data, I get the error below -
"The model backing the 'ApplicationDbContext' context has changed since the database was created. Consider using Code First Migrations to update the database"
How do I enable automatic schema updates when my model changes? I have "AutomaticMigrationsEnabled" my Configuration.cs set to true. Do I need to set something in my global.asax or Web.Config? What am I missing?
On my local server I can run Update-Database. How do I make this automatically happen in production whenever I push model updates?
UPDATE:
I was able to get rid of the error in production by following the steps in Using Entity Framework (code first) migrations in production
However I am not sure if this is the best way to fix the problem. Or if I wanted production to keep running this line every time the application starts.
Database.SetInitializer<ApplicationDbContext>(new
MigrateDatabaseToLatestVersion<ApplicationDbContext, Configuration>());
When you use MigrateDatabaseToLatestVersion it will indeed run your migrations for you. So you definitely need that or one of the alternatives like using DbMigrator in code or generating a script (update-database -Script).
These will run the migrations in your folder. The problem is you have AutomaticMigrationsEnabled = true in your configuration. This tells EF to just automatically update your database and does not create the code based migration file.
There are a couple of solutions. First, you could add a manual migration before you deploy (add-migration MyMigrationName) or you could switch your initializer to something like CreateDatabaseIfNotExists and then call the migrations in code as shown above.
See here for a detailed explanation.
I am working on an ASP.NET MVC project with Entity Framework with code first from database. I get the models for each table in the database. I made some changes in the models, enabled migrations and when I initial the migration I get an error:
There is already an object named 'TableName' in the database."
I tried with update-database -force but didn't help. The initial migration creates the tables that already exist!
How to make the initial migration apply the changes on the models and not create the tables from beginning?
And what is the best practice to sync changes between database and models in this case?
try to Run the
Add-Migration InitialCreate –IgnoreChanges
command in Package Manager Console. This creates an empty migration with the current model as a snapshot. and then Run the
Update-Database
command in Package Manager Console. This will apply the InitialCreate migration to the database. Since the actual migration doesn’t contain any changes, it will simply add a row to the __MigrationsHistory table indicating that this migration has already been applied.
see this
then change your models and add migration.
another approach is to simply comment all the code on up and down methods
Best and working For me idea is to comment all the code in UP and Down functions of Initial migration file and then fire
dotnet ef database update this should work fine,make sure you update migration before commenting out initial migration
If none of those answers work for you, you may check if in your code you use the method
context.Database.EnsureCreated()
Be aware that that method doesn't apply any migrations
(source) (you can check this making a sql query to the database and like "select * from __EfMigrationHistory" and be sure that there are no migrations on that database.
EF provide a really good method to help this that is
context.Database.Migrate()
that no only it will ensure that you have a database, but also use migrations and migrate yout db to the last version.
Hope it helps
This error appears when you deleted previous migrations and your new migration try to create new table that already exist. Recover previous migration and everything will be ok.
Amr Alaa solution works, but the database didn't migrate to the latest model.
Here's how it worked (using automatic migration) :
Delete Migrations folder
Execute enable-migrations
Set this two properties to true in the newly created Configuration.cs
public Configuration()
{
AutomaticMigrationsEnabled = true;
AutomaticMigrationDataLossAllowed = true;
}
Execute Update-Database -Force
Your database will be updated to latest scheme and ready.
hope this helps.
I've got this error for the 762nd time but this time I am getting it as soon as I attempt to access my Production site, straight after deleting the 'production' database on Azure and then publishing my site.
The model backing the 'PropertyContext' context has changed since the database was created. Consider using Code First Migrations to update the database
I deleted the database because I couldn't fix this issue any other way but it still doesn't work.
Some important points:
I'm using EF6 and publishing to Azure.
This is 1 of 2 projects/sites that uses the same Repo project. I have no
problems with the other one, just this one.
I have tried publishing the problem project first (after deleting the db) and
second with the same result.
I have tried deleting both WEBSITES and the DB from Azure and starting again
I have tried deleting all migrations and starting with a fresh data model
I have tried the following in my Global.asax (in both projects)
Database.SetInitializer PropertyContext>(null); <-- SO won't let me put the first <
and
Database.SetInitializer(new MigrateDatabaseToLatestVersion<PropertyContext, MyConfiguration>());
new PropertyContext().Database.Initialize(true);
I'm using .net 4.5
Why am I getting this error on a new database and how can I get this site to work?
Just ran into the same error in ASP.Net application. In my case I did not use Code First, but I used standard ASP.Net authentication provider which apparently uses Code First, and authentication was broken because of this issue.
Here is quick and dirty solution is you don't care much about existing user records:
For me the solution was to drop the dbo.__MigrationHistory table, authentication started working fine after that. Be aware! This solution is not for everyone! This will fix the problem, but it is potentially risky.
If you cannot afford to lose data in AspNet* tables:
ASP.Net authentication provider automatically creates tables in your database:
AspNetRoles
AspNetUsers
AspNetUserRoles
AspNetUserClaims
AspNetUserLogings
The tables are empty by default, if you haven't created any new logins for your web site, you can use "quick and dirty" solution above. If you do care about preserving user information or just curios how Code First migrations work, follow these steps:
Open your Web.config file and check the name of the connection string you have for your database. It will be one of the records under <connectionStrings> element.
Open Package Manager Console:
Tools –> Library Package Manager –> Package Manager Console
In Package Manager Console window, use a drop-down to set Default Project. Make sure this is the project that contains ASP.Net authentication provider code.
Execute command:
Update-Database -ConnectionStringName MyConnectionStringName
Replace the MyConnectionStringName with the actual name you looked up in web.config.
As a result of this command you will see a new folder "Migrations" with a bunch of code generated by the Update-Database command. Re-build and re-deploy your app, your new migration code will be executed on startup and would bring the database schema in sync with an updated version of ASP.Net authentication provider code.
When using Code First with Migrations, your database creates a table called __MigrationHistory to track the current schema. When you run your application your Entity Framework will check this table to make sure that the database schema matches your database entities. If they do not match, you will get this error.
To update your database follow these steps:
Open the Package Manager Console (View -> Other Windows -> Package Manager Console) in Visual Studio
In the Package Manager Console Window, there is a drop down with your projects in, make sure it is set to the project that contains your DbContext
Make sure that the project that contains your App.Config / Web.Config file is "Set as Startup Project" (If you have multiple Configs, it must be the one with the Database Connection String defined.
Type Update-Database -ConnectionStringName MyConnString where MyConnString is the name (not the actual connection string) of your connection string in your App.Config / Web.Config
If you get an error like this: "Unable to update database to match the current model because there are pending changes and automatic migration is disabled."
You should enable Automatic Migrations and try again.
To enable Automatic Migrations
In the Migrations folder (in the project with your DbContext), open Configuration.cs.
Make sure the Constructor contains: AutomaticMigrationsEnabled = true;
To stop Entity Framework/DbContext from monitoring changes on your database you could simply delete the __MigrationHistory table in your database. It is then up to you to make sure that the database remains updated manually.
MSDN article here
The solution from this is to use the static method SetInitializer and bind to the context a Null value. If you are working on a Web solution, the best position to write the code is in the Application_Start of your Global.asax.cs file.
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterRoutes(RouteTable.Routes);
//...
Database.SetInitializer<MyContext>(null);
}
I got a similar problem this morning. Suddenly the error appeared and couldn't be resolved:
The model backing the 'ApplicationDbContext' context has changed since
the database was created. Consider using Code First Migrations to update
the database
I have one project for MVC and another project for the model, context and repositories. I've been working on it for weeks but today it said stop.
I have tried to delete database, enable-migration, add-migration and update-database so many times that I've lost count. I've added initializers to MigrateDatabaseToLatestVersion as well as DropCreateDatabaseIfModelChanges. All in vain...
What finally made it work was to move model, context and repositories into the MVC project (not something I was keen on)...then it worked right out of the box without any code changes at all (besides namespaces)! Very strange...
I've read so many blog posts during the day trying to solve this problem. One of them (I don't know which one) mentioned a bug in Visual Studio 2013 where reference to DLL files weren't always updated as they should, suggesting that my MVC project missed out something when I was running add-migration and update-database in my separate project. But it's just a guess.
I'm using EF 6.1 and .Net 4.5.1 in my solution.
Got a similar problem! Answer is here
http://www.asp.net/mvc/overview/older-versions/getting-started-with-aspnet-mvc3/cs/adding-a-new-field
(Rick Anderson)
There are two approaches to resolving the error:
Have the Entity Framework automatically drop and re-create the database based on the new model class schema. This approach is very convenient when doing active development on a test database, because it allows you to quickly evolve the model and database schema together. The downside, though, is that you lose existing data in the database — so you don't want to use this approach on a production database!
Explicitly modify the schema of the existing database so that it matches the model classes. The advantage of this approach is that you keep your data. You can make this change either manually or by creating a database change script.
I have spent some hours trying to solve this problem. One project was working, the other one wasn't.
I had different projects referencing different versions of Entity Framework. In my case, I had a Console app and a Windows Service app, both referencing a third project containing code first classes and DbContext.
After running Update-Package EntityFramework everything worked fine in both projects.