在 Entity Framework Core 中使用 Update-Database 添加新列

Question

May be i'm missing something very obvious. But i haven't been able to figure out a way to add a new column to an existing table/model in EF Core.

This is the documentation that I'm following: https://docs.microsoft.com/en-us/ef/core/miscellaneous/cli/powershell

And this is what i have done so far:

1. Created migration using this command: "Add-Migration -Name CodingSoldierDbContextMigration -OutputDir Migrations -Context CodingSoldierDbContext"
2. Updated database using the command: "Update-Database -Migration CodingSoldierDbContextMigration -Context CodingSoldierDbContext". Tables got created in the Database.
3. Now i need to add a new column to an existing table. I add that column to the model in the.cs file. And i remove the existing migration: "Remove-Migration -Force -Context CodingSoldierDbContext"
4. Now i re-run the commands in steps 1 and 2. Add-Migration works and migration gets created. But Update-Database fails with the error: "There is already an object named 'AspNetRoles' in the database." which means the table is already present in the database which makes sense.

So how do i update an already existing table table? 2 ways i can think of are:

1. Drop the database. Create migration and update database. But all data will be gone.
2. Add column in the model. Manually update the Table using a SQL script to add the new column.

But i feel there should be a better way to do this.

Answer 1

This is how i resolved the issue. Not sure if it is the perfect way.

Key is NOT to delete the initial migration, before you create the new migration.

Adding the steps here:

1. Creating initial migration: "Add-Migration -Name CodingSoldierDbContextMigration -OutputDir Migrations -Context CodingSoldierDbContext"
2. Updated database using the command: "Update-Database -Migration CodingSoldierDbContextMigration -Context CodingSoldierDbContext". Tables gets created in the Database.
3. Added new field in one of the models.
4. Creating updated migration: "Add-Migration -Name CodingSoldierDbContextMigrationUpdated -OutputDir Migrations -Context CodingSoldierDbContext". This migration will have code only for updating the existing table.
5. Updating DB with the updated migration: "Update-Database -Migration CodingSoldierDbContextMigrationUpdated". Ideally this should have resolved it. But for me, it gave error because(as from Verbose logs) it was trying to update with initial migration: "CodingSoldierDbContextMigration", i don't know why.
6. So i generate scripts using Script-Migration: "Script-Migration -From CodingSoldierDbContextMigration -Idempotent -Output C:\\MigrationScript.sql -Context CodingSoldierDbContext". It generated the script which had changes only from the updated migration. Running that script in DB created the column and added the migration entry in "__EFMigrationsHistory" table.

Answer 2

This is a way which helped me to add a new column to the existed database without losing data:

1. I've written this command into Package Manager Console to the Project which contains my Model

   add-migration MyFirstMigration

2. The above command created a class with a lot of code:

    public partial class MyFirstMigration : Migration { protected override void Up(MigrationBuilder migrationBuilder) { ... // The code is omitted for the brevity ... } }

3. I've deleted all generated code and added the following code snippet into the above method Up(MigrationBuilder migrationBuilder) :

    protected override void Up(MigrationBuilder migrationBuilder) { migrationBuilder.AddColumn<string>("Password", "Users", "varchar(255)", unicode:false, maxLength: 255, nullable: true); }

4. Then it is necessary to write the following command into Package Manager Console to add a column into your database:

    Update-Database

Answer 3

I kinda did a mixture of what @Boney and @StepUp suggested and it ran without hitches. Here's what I did. Assume a have a table Period that I decided to add an additional column PeriodTypeId.

1. Add another migration. eg

Add-Migration -Name OVCDbMigrationsUpdated -Context DbContext

This created a new migration file with name: OVCDbMigrationsUpdated.

2. Run Update-Database targeting the new migration file. eg

Update-Database -verbose -Migration OVCDbMigrationsUpdated -Context DbContext

My DB was updated successfully with the new column.

Answer 4

I was running into a similar issue with EF Core and an existing database with some of the model fleshed out, but I was adding a new model (that already had a table) and was getting the error

There is already an object named 'tableN' in the database.

The way I got this to work on an existing database was:

1. Download Repo
2. Run all migrations up to date (if you have a database with migrations) If you don't, then just create an initial "dummy" migration and apply that
3. Create a baseline migration prior to making any changes in your model/code
4. Update your code with any changes to your database
5. Create another migration
6. Delete the initial baseline migration
7. update-database

Answer 5

Update-Database will work if we exclude previous migration from solution and then run update-database cmd. However we can include again for DB definition. Directly it won't work in case of EF core + postgresql.

Answer 6

One doesn't need to remove the migration or delete the table. If you want to add a new column to the database table which was already created using add-migration and update-database, one needs to again run the command (add-migration) in nuget package manager console with a new migration name (add-migration "Name2") and then run the command (update-database). The system will know what changes have been made and creates a new migration file but the new column will be added to the same database table where you want to add the column.