wheels dbmigrate down

Rollback the last executed database migration.

Synopsis

wheels dbmigrate down

Alias: wheels db down

Description

The dbmigrate down command reverses the last executed migration by running its down() method. This is useful for undoing database changes when issues are discovered or when you need to modify a migration. The command ensures safe rollback of schema changes while maintaining database integrity.

Parameters

None.

Examples

Rollback the last migration

wheels dbmigrate down

This will execute the down() method of the most recently applied migration, reverting the database changes.

Use Cases

Fixing Migration Errors

When a migration contains errors or needs modification:

# Run the migration
wheels dbmigrate up

# Discover an issue
# Rollback the migration
wheels dbmigrate down

# Edit the migration file
# Re-run the migration
wheels dbmigrate up

Development Iteration

During development when refining migrations:

# Apply migration
wheels dbmigrate up

# Test the changes
# Need to modify? Rollback
wheels dbmigrate down

# Make changes to migration
# Apply again
wheels dbmigrate up

Emergency Rollback

When a migration causes issues:

# Check current migration status
wheels dbmigrate info

# Rollback the problematic migration
wheels dbmigrate down

# Verify rollback
wheels dbmigrate info

Important Considerations

Data Loss Warning

Rolling back migrations that drop columns or tables will result in data loss. Always ensure you have backups before rolling back destructive migrations.

Down Method Requirements

For a migration to be rolled back, it must have a properly implemented down() method that reverses the changes made in the up() method.

Migration Dependencies

Be cautious when rolling back migrations that other migrations depend on. This can break the migration chain.

Best Practices

1. Always implement down() methods: Even if you think you'll never need to rollback

2. Test rollbacks: In development, always test that your down() method works correctly

3. Backup before rollback: Especially in production environments

4. Document destructive operations: Clearly indicate when rollbacks will cause data loss

Notes

• Only the last executed migration can be rolled back with this command

• To rollback multiple migrations, run the command multiple times

• If already at version 0, displays: "We're already on zero! No migrations to go to"

• Automatically runs dbmigrate info after successful rollback

• The migration version is removed from the database tracking table upon successful rollback

• Some operations (like dropping columns with data) cannot be fully reversed

• When migrating to version 0, displays: "Database should now be empty."

Related Commands

• wheels dbmigrate up - Run the next migration

• wheels dbmigrate reset - Reset all migrations

• wheels dbmigrate info - View migration status

• wheels dbmigrate exec - Run a specific migration