How do I apply migrations in Yii?

The main method to apply database migrations in Yii is using the built-in migration tool via the command line. 1. Migration files are PHP classes stored in the migrations folder with timestamp-based names, used to modify the database schema. 2. To apply all pending migrations, run yii migrate/up, optionally adding --interactive=0 to skip confirmation or --limit=1 to apply one at a time. 3. To roll back migrations, use yii migrate/down with an optional --limit flag. 4. For a clean reset, use yii migrate/down --limit=999 followed by yii migrate/up --limit=999, though this should be avoided in production. 5. When working with modules or multiple directories, specify a custom path using --migrationPath.

When you're working with Yii and need to apply database migrations, the main method is using Yii's built-in migration tool via the command line. It’s straightforward once you understand how the system organizes and runs migration files.

Understanding Migration Files

Before applying migrations, it helps to know what they are. Migration files in Yii are PHP classes that contain instructions for modifying your database schema—like creating tables, adding columns, or changing indexes.

These files are stored in the migrations folder of your application or module by default. Each migration file has a timestamp-based name (e.g., m230101_000001_create_table_user.php) so Yii can determine the correct order when applying them.

If you haven't created any yet, use this command to generate one:

yii migrate/create create_table_something

This gives you a template to fill in with your actual DB changes.

Applying Migrations Step by Step

Once you have your migration files ready, applying them is simple:

• Make sure you're in your project root directory where the yii console script is located.
• Run this command:

  yii migrate/up

Yii will show you a list of pending migrations and ask for confirmation. Type y and hit Enter to proceed.

You can also skip the confirmation prompt by adding --interactive=0:

yii migrate/up --interactive=0

By default, it applies all pending migrations. If you only want to apply one at a time, add the --limit=1 flag:

yii migrate/up --limit=1

This comes in handy during testing or when troubleshooting a specific migration.

Rolling Back or Resetting Migrations

Sometimes things go wrong or you need to undo changes. Yii lets you roll back migrations using:

yii migrate/down

Just like applying, you can limit how many steps to roll back:

yii migrate/down --limit=2

Be cautious though—rolling back deletes data if your migration includes dropping tables or columns.

For a clean start (not recommended on production), you can reset all migrations:

yii migrate/down --limit=999

Then reapply them:

yii migrate/up --limit=999

This is useful during development or when setting up a new environment from scratch.

Managing Multiple Migration Paths

If your app uses modules or multiple migration directories, you can specify which path to use:

yii migrate/up --migrationPath=@app/modules/user/migrations

This tells Yii to look in a custom location instead of the default @app/migrations.

It’s helpful when maintaining separate databases per module or managing shared components across projects.

That's basically how you handle migrations in Yii. It's not complicated once you get used to the commands and structure, but it's powerful enough for most real-world scenarios.

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