I have changed my model and is scaffolding a new migration using the Add-Migration package manager command.
However, for some reason, EF think that I have been renaming an object for one of my classes. The class names are similar in name and have similar properties and relationships.
The problem is that the Update-Database command fails because of the rename. The very first command is RenameTable() and later on the migration tries to delete an index on the table that has been renamed (and doesn't exist anymore).
I would like to force EF to scaffold a migration where the old table is dropped and a new one is created instead. How do I achieve this? My impression was that EF can't be "smart" when figuring out renames and should always drop tables that are no longer mapped to an entity.
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Hi I created my database using Entity Framework core with code first approach. Now there is a change in the column type from int to varchar/string? I can change the column from the database itself but my understanding is that it won't be a good idea and would create issues. I searched through but I didn't get my answer on the net for Entity framework core.
You should use EF Core migrations to update your db schema. The documentation is pretty good, so make sure to go through it.
However, this is a summary of how the process would be:
Make the change in your model (which by convention will be automatically detected. Alternatively, use the Fluent API in your DB Context OnCreate method or in your EntityConfigurations).
Add a migration running the following CLI command : dotnet ef migrations add SomeDescriptiveNameAboutWhatThisMigrationWillDo.
A migration file with an Up and Down method will be automatically generated. The Up will be run when you apply the migration, and the Down if you ever decide to revert it . You could add changes to the automatically scaffolded migration file. Based on the code in the migration file, EF Core will then generate a SQL script and apply the changes to the DB.
Once you have added (and maybe edited) the migration file, you need to apply it to the DB. You do that by running dotnet ef migrations update.
EF Core tracks all applied migrations in a table in your DB called by default __EFMigrationsHistory
In your particular case of changing a column type, EF Core might try to drop the column and recreate it, which will result in data loss. If you wanna keep your data, I would recommend altering the migration script to actually split the process in two: first add a new column with the new type and a slightly different name, then write some custom SQL to migrate data from the old column to the new one, then delete the old column and finally rename the new column to the correct name. To be honest, I am not sure if there is some custom migration operation that will out of the box change the data type without data loss, there might be.
To double check if the migration will generate data loss or check if it will do what you expect it to do, you can generate the SQL script that will be used by running dotnet ef migrations script <from migration> <to migration>. After reviewing it, you can either copy/paste and run the script in your DB, or just run the command detailed in step 4 above.
You can modify your database schema to match your domain model with the add-migration command.
After changing the type of the property on your c# class from int to string, simply run
add-migration <SomeDescriptiveName>
After the creation of the migration files, you can apply them with the update-database command.
You can read more about migrations here.
I have a .net core 2 project, along with Entity framework Core.
I have an existing database, and I've mapped them out to database entities in code.
The problem is that when I add a migration, expectedly it picks up my entity as a new table, however it is an existing table. The table shares the same name.
I suppose, I could just remove the contents of the Up method of the migration, but I want to know if there is a proper way instead of a workaround.
So, what I am asking is how can I tell entity framework core that this table is already existing?
EF 6 had an -IgnoreChanges option that would just take a snapshot with no Up() code, but that feature is not in EF Core (yet). See here.
If you comment out the Up() code as you have suggested that will indeed capture a snapshot of your existing objects and subsequent migrations will be incremental.
I'm using EF6 code-first migrations for existing database but initial DbContext does not fully cover existing schema (since it's massive). So from time to time I have to make updates to the model in database-first style. For example when I need an entity mapping for a table or a column that is already in the database but not reflected in the code I do the following:
Make all change (add new entity, rename the column mapping or add new property)
Scaffold migration representing the latest model snapshot stub_migration
Copy-paste latest serialized model from stub_migration to the last_migration resource file
Delete stub_migration
Revert last_migration in database
Update-Database so that model snapshot in [__MigrationHistory] table would be also updated
I understand that this aproach is a bit hackish and the proper way would be to leave empty stub_migration but this would force lots of empty migrations which I would rather avoid.
Looking at a similar scenario from MSDN article (Option 2: Update the model snapshot in the last migration) I wouldn't imagine that there is an easier way rather than writing power shell script, managed code or both to make it work. But I would rather ask community first before diving deep into it.
So I wonder: is there a simple way to automate generation of new model snapshot in latest migration and reaplying it?
I'm doing something similar. I have a large database and I am using the EF Tools for VS 2013 to reverse engineer it in small parts into my DEV environment. The tool creates my POCOs and Context changes in a separate folder. I move them to my data project, create a fluent configuration and then apply a migration (or turn automigration on).
After a while I want a single migration for TEST or PROD so I roll them up into a single migration using the technique explained here: http://cpratt.co/migrating-production-database-with-entity-framework-code-first/#at_pco=smlwn-1.0&at_si=54ad5c7b61c48943&at_ab=per-12&at_pos=0&at_tot=1
You can simplify the steps for updating DbContext snapshot of the last migration applied to database by re-scaffolding it with Entity Framework:
Revert the last migration if it is applied to the database:
Update-Database -Target:Previous_Migraton
Re-scaffold the last migration Add-Migration The_name_of_the_last_migration which will recreate the last migrations *.resx and *.Designer.cs (not the migration code), which is quite handy.
Those 2 steps are covering 4 steps (2-5) from original question.
You can also get different bahavior depending on what you want by specifying the flags -IgnoreChanges and (or) -Force
And by the way, the major problem with the updating the DbContext snapshot is not how to automate those steps, but how to conditionally apply them to TEST/PROD environments depending on whether you actually want to suppress the warning because you've mapped existing DB-first entities in you DbContext or you want it it to fail the build in case you've created new entities and forgot to create a code-first migration for them.
So, try to avoid those steps altogether and maybe create empty migrations when you just want to map existing tables to your code.
I'm using an existing database and I have mapped one of the tables as an entity (as i needed to map a foreign key).
So when it comes to initialising this database I would like EF to ignore this entity since it already exists.
How would I go about doing this?
You should create an empty migration as the first migration with the -IgnoreChanges flag to allow Entity Framework to get a snapshot of the existing database.
So out of the gate use:
Add-Migration InitialMigration -IgnoreChanges
and that will create a blank migration but it will update the Entity Framework metadata allowing the existing tables to exist and not be touched by migrations.
Also to be mentioned that the naming conventions that Entity Framework expects and your database schema may differ. You may need to manually setup the foreign keys using the Fluent API.
I didnt check with EF 6 specifically, but I think default EF behavious is that when the database exists, then it presume all model be ready and therefore will create no tables. If you want your initialization code to create tables with code first, use initialization code for prepare data. Look here :
http://www.entityframeworktutorial.net/code-first/seed-database-in-code-first.aspx
I have a database that I have been using and updating with Code First Migrations. I now want to add a second project that also uses the database with additional fields on some of the existing tables.
I assumed the best way to do this was to introduce a second datacontext with the second project.
As EF6 allows multiple DataContexts with additional ContextKey field, however enabling migrations and running with
PM> add-migration InitialCreate -IgnoreChanges
Causes another __MigrationHistory table to be created when there is already one there from the first project. I only need the row to be added InitialCreate.
I am not sure how I can suppress the generation of the __MigrationHistory table.
Wayne