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The most recently generated migration and its related database changes will be reversed. If the migration being rolled back involves the removal of columns or tables, it's important to recognize that there is a possibility of data loss.
6 de ago. de 2020 · Review. The Last Migration by Charlotte McConaghy review – aching, poignant and pressing debut. The dreamy, slippery novel melds adventure with climate fiction as its protagonist follows the...
- Overview
- Add a migration
- Customize migration code
- Remove a migration
- Listing migrations
- Checking for pending model changes
- Resetting all migrations
- Additional resources
As your model changes, migrations are added and removed as part of normal development, and the migration files are checked into your project's source control. To manage migrations, you must first install the EF Core command-line tools.
After your model has been changed, you can add a migration for that change:
•.NET Core CLI
•Visual Studio
The migration name can be used like a commit message in a version control system. For example, you might choose a name like AddBlogCreatedTimestamp if the change is a new CreatedTimestamp property on your Blog entity.
Three files are added to your project under the Migrations directory:
•XXXXXXXXXXXXXX_AddCreatedTimestamp.cs--The main migrations file. Contains the operations necessary to apply the migration (in Up) and to revert it (in Down).
Column renames
One notable example where customizing migrations is required is when renaming a property. For example, if you rename a property from Name to FullName, EF Core will generate the following migration: EF Core is generally unable to know when the intention is to drop a column and create a new one (two separate changes), and when a column should be renamed. If the above migration is applied as-is, all your customer names will be lost. To rename a column, replace the above generated migration with the following:
Adding raw SQL
While renaming a column can be achieved via a built-in API, in many cases that is not possible. For example, we may want to replace existing FirstName and LastName properties with a single, new FullName property. The migration generated by EF Core will be the following: As before, this would cause unwanted data loss. To transfer the data from the old columns, we rearrange the migrations and introduce a raw SQL operation as follows:
Arbitrary changes via raw SQL
Raw SQL can also be used to manage database objects that EF Core isn't aware of. To do this, add a migration without making any model change; an empty migration will be generated, which you can then populate with raw SQL operations. For example, the following migration creates a SQL Server stored procedure: This can be used to manage any aspect of your database, including: •Stored procedures •Full-Text Search •Functions •Triggers •Views
Sometimes you add a migration and realize you need to make additional changes to your EF Core model before applying it. To remove the last migration, use this command.
•.NET Core CLI
•Visual Studio
After removing the migration, you can make the additional model changes and add it again.
Warning
Avoid removing any migrations which have already been applied to production databases. Doing so means you won't be able to revert those migrations from the databases, and may break the assumptions made by subsequent migrations.
You can list all existing migrations as follows:
•.NET Core CLI
Sometimes you may want to check if there have been any model changes made since the last migration. This can help you know when you or a teammate forgot to add a migration. One way to do that is using this command.
You can also perform this check programmatically using context.Database.HasPendingModelChanges(). This can be used to write a unit test that fails when you forget to add a migration.
In some extreme cases, it may be necessary to remove all migrations and start over. This can be easily done by deleting your Migrations folder and dropping your database; at that point you can create a new initial migration, which will contain your entire current schema.
It's also possible to reset all migrations and create a single one without losing your data. This is sometimes called "squashing", and involves some manual work:
1.Back up your database, in case something goes wrong.
2.In your database, delete all rows from the migrations history table (e.g. DELETE FROM [__EFMigrationsHistory] on SQL Server).
3.Delete your Migrations folder.
4.Create a new migration and generate a SQL script for it (dotnet ef migrations script).
•Entity Framework Core tools reference - .NET Core CLI : Includes commands to update, drop, add, remove, and more.
•Entity Framework Core tools reference - Package Manager Console in Visual Studio : Includes commands to update, drop, add, remove, and more.
4 de ago. de 2020 · Charlotte McConaghy. 4.14. 74,038 ratings10,891 reviews. Goodreads Choice Award. Nominee for Best Fiction (2020) Franny Stone has always been the kind of woman who is able to love but unable to stay.
29 de out. de 2021 · The Arctic terns, a species evolved to fly across the world on 40,000km annual journeys, are on their last migration to Antarctica. Into the mix is Franny, an environmentalist and woman with a...
4 de ago. de 2020 · "A dark past. An impossible journey. The will to survive. How far you would you go for love? Franny Stone is determined to go to the end of the earth, following the last of the Arctic terns on what...
18 de ago. de 2020 · Review. 18 August 2020. The Last Migration by Charlotte McConaghy is One of the Best Books of the Year. For readers of Station Eleven and Everything I Never Told You, a novel set on the brink of catastrophe, as a young woman chases the world’s last birds – and her own final chance for redemption. A dark past. An impossible journey.
