**Course Title:** Mastering Symfony: Building Enterprise-Level PHP Applications **Section Title:** Doctrine ORM and Database Integration **Topic:** Creating database schemas and migrations ### Overview In this topic, we will explore how to create database schemas and migrations using Doctrine ORM in a Symfony application. By the end of this section, you will understand the importance of database schema management, learn how to create and update your database schema, and understand how to write database migrations. ### What are database schemas and migrations? A database schema refers to the overall structure or organization of a database, including the relationships between different tables. In Doctrine ORM, the schema is defined by the metadata of your entities. A migration is a way to modify your database schema by executing a series of SQL commands. Migrations provide a way to manage changes to your database schema over time, allowing you to easily deploy changes to your database schema across different environments. ### Creating database schemas In Doctrine ORM, the database schema is created from the metadata of your entities. To create the database schema, you can use the `doctrine:schema:create` command: ```bash php bin/console doctrine:schema:create ``` This command will create the database schema based on the metadata of your entities. You can also use the `--dump-sql` option to dump the SQL queries that would be executed without actually executing them: ```bash php bin/console doctrine:schema:create --dump-sql ``` ### Updating database schemas When you make changes to your entities, you need to update your database schema to reflect these changes. To update the database schema, you can use the `doctrine:schema:update` command: ```bash php bin/console doctrine:schema:update --force ``` This command will update the database schema by comparing the current schema with the schema defined by the metadata of your entities. The `--force` option is required to actually execute the SQL queries. ### Writing database migrations Migrations provide a way to manage changes to your database schema over time. To create a new migration, you can use the `doctrine:migrations:generate` command: ```bash php bin/console doctrine:migrations:generate ``` This command will create a new migration class in the `src/Migrations` directory. You can then modify this class to define the SQL queries that should be executed to apply the migration. For example, let's say we want to add a new column to an existing table. We can modify the migration class as follows: ```php use Doctrine\DBAL\Filesystem\Folder; use Doctrine\DBAL\Migrations\AbstractMigration; use Doctrine\DBAL\Schema\Schema; class Version20221215143059 extends AbstractMigration { public function up(Schema $schema) { $this->addSql('ALTER TABLE user ADD email VARCHAR(255) NOT NULL'); } public function down(Schema $schema) { $this->addSql('ALTER TABLE user DROP email'); } } ``` In this example, the `up` method defines the SQL query that should be executed to apply the migration, and the `down` method defines the SQL query that should be executed to revert the migration. To apply the migration, you can use the `doctrine:migrations:migrate` command: ```bash php bin/console doctrine:migrations:migrate ``` This command will execute the SQL queries defined in the migration class. ### Best Practices Here are some best practices to keep in mind when creating database schemas and migrations: * Use entities to define your database schema. * Use migrations to manage changes to your database schema over time. * Use the `doctrine:schema:create` and `doctrine:schema:update` commands to create and update your database schema. * Use the `doctrine:migrations:generate` command to create new migrations. * Test your migrations thoroughly to ensure that they work correctly. ### Conclusion In this topic, we learned how to create database schemas and migrations using Doctrine ORM in a Symfony application. We saw how to create and update database schemas using the `doctrine:schema:create` and `doctrine:schema:update` commands, and how to write and apply database migrations using the `doctrine:migrations:generate` and `doctrine:migrations:migrate` commands. ### What's Next? In the next topic, we will explore how to define entities, relationships (one-to-one, one-to-many, many-to-many). ### Resources * [Doctrine ORM documentation on schema management](https://www.doctrine-project.org/projects/orm/2.10/en/latest/reference/schema-management.html) * [Symfony documentation on database schema management](https://symfony.com/doc/current/doctrine/dbal.html#schema-management) ### Comments and Questions We encourage you to leave a comment or ask a question if you need further clarification on any of the topics covered in this section.