How To Handle Custom S/DQL Queries On Different Database Engine with DoctrineExpression

In the journey of building robust Symfony projects, there often comes a point where simple Entity Repository methods like findBy() are no longer sufficient. For me, that point arrived, and I reached for the power of custom DQL queries to handle more complex data retrieval needs. At the time, I was using MySQL as my default database. Everything worked perfectly until I containerized my project and decided to switch over to PostgreSQL for performance and feature flexibility.

But, oh no! My DQL queries immediately began throwing errors ?‍?. What went wrong? My custom DQL syntax was perfectly crafted for MySQL’s quirks and functions but was incompatible with PostgreSQL. The choice was now between two challenging paths:

Option 1: Revert back to MySQL to keep things safe.

But what if I wanted to share the project with a developer who preferred PostgreSQL?

Option 2: Rewrite my DQL to support PostgreSQL.

But, what if I needed to switch back to MySQL later? Or what if I used a tool that only supported MySQL?

Choosing between these wasn’t easy—both options could lock me into a single database environment, limiting flexibility in future tech choices. So, I decided to take a different approach and created a solution to dynamically handle database-specific queries in a clean, reusable way.

Introducing DoctrineExpression

DoctrineExpression is a PHP library designed to enable cross-platform, database-agnostic DQL and SQL queries in Symfony or any project that utilizes doctrine. With DoctrineExpression, you can define custom syntax for each database platform (MySQL, PostgreSQL, SQLite, etc.), and it will select the correct expression based on the current database driver. It works like this:

1. Define Multiple Expressions: Write different syntax for each database driver, specifying unique queries that match each platform’s functions and quirks.
2. Automatic Driver Detection: DoctrineExpression checks the Doctrine platform in use, then automatically applies the correct syntax for MySQL, PostgreSQL, or any other supported database.
3. Future-Proof Flexibility: By allowing you to switch databases easily, DoctrineExpression future-proofs your code, ensuring that you can support multiple databases without extensive rewrites.

Now, with DoctrineExpression, I have the flexibility to use either MySQL or PostgreSQL (or even SQLite), keeping my code clean and maintainable. I can switch platforms based on project requirements, team preferences, or performance considerations without worrying about refactoring every custom query.

How DoctrineExpression Solves the Problem

Let’s look at a simple example where we need to retrieve users who registered within the last 24 hours. This is often handled differently in MySQL and PostgreSQL.

Without DoctrineExpression

1. MySQL: Uses DATE_SUB(NOW(), INTERVAL 1 DAY) to find records within the last 24 hours.
2. PostgreSQL: Uses NOW() - INTERVAL '1 day' for the same query.

Here’s how you might write these separately without DoctrineExpression:

// MySQL Query
$mysqlQuery = $entityManager->createQuery(
    "SELECT u FROM App\Entity\User u WHERE u.registeredAt > DATE_SUB(NOW(), INTERVAL 1 DAY)"
);

If you were using PostgreSQL, you would write in this format:

// PostgreSQL Query
$postgresQuery = $entityManager->createQuery(
    "SELECT u FROM App\Entity\User u WHERE u.registeredAt > NOW() - INTERVAL '1 day'"
);

If you switch databases, you'll need to modify this code, which is inconvenient and error-prone.

With DoctrineExpression

With DoctrineExpression, you define both syntaxes and let the library handle the rest:

use Ucscode\DoctrineExpression\DoctrineExpression;
use Ucscode\DoctrineExpression\DriverEnum;

// Create an expression instance with an EntityManager argument
$expression = new DoctrineExpression($entityManager);

// Registration S/DQL for varying database
$expression
    ->defineQuery(DriverEnum::PDO_MYSQL, function($entityManager) {
        return $entityManager->createQuery(
            "SELECT u FROM App\Entity\User u WHERE u.registeredAt > DATE_SUB(NOW(), INTERVAL 1 DAY)"
        );
    })
    ->defineQuery(DriverEnum::PDO_PGSQL, function($entityManager) {
        return $entityManager->createQuery(
            "SELECT u FROM App\Entity\User u WHERE u.registeredAt > NOW() - INTERVAL '1 day'"
        );
    });

// Fet any of the defined query based on the active doctine driver being used
$query = $expression->getCompatibleResult();

Now, DoctrineExpression checks the database platform in use and dynamically inserts the correct syntax for the current environment. It doesn't matter anymore you’re using MySQL or PostgreSQL, it will select the correct expression, saving you from having to modify your queries every time you switch platforms and also removes the boilerplate of using if-else repeatedly

In Conclusion:

DoctrineExpression saves time and effort by allowing you to use different databases without rewriting your queries. It’s particularly useful in containerized or multi-environment projects where you need to use custom syntax but database preferences may change depending on deployment needs or team familiarity. Give it a try, and let me know how it works for you!

Check out DoctrineExpression on GitHub

Happy coding!

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