How do you write raw SQL queries in ActiveRecord?

ActiveRecord is a powerful ORM (Object-Relational Mapping) library in Ruby on Rails that allows developers to interact with the database using Ruby code. However, there are scenarios where using raw SQL queries in ActiveRecord can be more efficient or necessary, such as for performance optimization or when dealing with complex queries that ActiveRecord cannot easily express.

Understanding Raw SQL with ActiveRecord

In Rails, ActiveRecord provides a variety of ways to write and execute raw SQL queries. Leveraging this capability can be particularly useful for optimizing query performance or executing complex database operations that are difficult to express through standard ActiveRecord methods.

When to Use Raw SQL in ActiveRecord

• Performance: Sometimes, raw SQL can be more performant than ActiveRecord's equivalent query, especially when dealing with complex joins or subqueries.
• Complex Queries: If a query involves complex SQL operations not supported directly by ActiveRecord, writing raw SQL is a straightforward choice.
• Database Specific Features: Use raw SQL when you need to leverage database-specific features that are not abstracted by ActiveRecord.

Executing Raw SQL Queries

Using find_by_sql

The find_by_sql method allows you to execute a raw SQL query and returns an array of model instances.

1users = User.find_by_sql("SELECT * FROM users WHERE age >= 18")
2users.each do |user|
3  puts user.name
4end
5

Using connection.execute

For more control, you can use the connection object to execute SQL directly. This is particularly useful for non-SELECT queries.

1User.connection.execute("UPDATE users SET active = true WHERE last_login > NOW() - INTERVAL '1 month'")
2

Parameterized Queries

Using parameterized queries helps in preventing SQL injection attacks. Instead of interpolating user input directly into your SQL string, use placeholders and bind variables.

1user_id = 1
2User.find_by_sql(["SELECT * FROM users WHERE id = ?", user_id])
3

Using pluck and select_all

pluck is a handy method when you want to retrieve a single column value. For raw SQL, consider using select_all for complex selections.

1names = ActiveRecord::Base.connection.select_all("SELECT name FROM users").map { |row| row['name'] }
2

Considerations and Best Practices

• Security: Always sanitize inputs when using raw SQL to prevent SQL injection. Use parameter binding instead of string interpolation.
• Readability and Maintainability: Raw SQL can become hard to read and maintain. Ensure that complex SQL logic is well-documented.
• SQL Standardization: Be aware of SQL dialect differences if you plan to switch databases.

Exploring Further

• Learn more about ActiveRecord Query Interface
• Dive deeper into SQL injection prevention techniques
• Explore Rails ActiveRecord documentation

Conclusion

Writing raw SQL queries in ActiveRecord can be a powerful tool when used correctly. It allows you to leverage the full capabilities of your database while still using the familiar Rails framework. Whether you're optimizing performance or handling complex queries, understanding how to integrate raw SQL with ActiveRecord effectively can greatly enhance your Rails applications.

Remember, the key is to use raw SQL judiciously by balancing performance needs with the readability and maintainability of your code. Check out our other development guides and tutorials for more in-depth knowledge and best practices!