Experience with relational and non-relational databases?

In working with relational databases (e.g., PostgreSQL, MySQL), I use SQL for complex queries, transactions, indexes, and data normalization. I apply ORM (e.g., Hibernate in Java) for ease of working with object models.

With non-relational databases (MongoDB, Redis, Cassandra), I have dealt with them when flexible schemas, caching, and processing large volumes of data at high speed are required. For example, Redis is used for storing sessions and fast operations, MongoDB for documents with dynamic structures.

Example of using Hibernate with PostgreSQL:

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String username;
    private String email;
    // getters and setters
}

// In the service
User user = entityManager.find(User.class, userId);

Thus, the choice of database depends on the task: relational for strict structure and complex relationships, non-relational for scalability and flexibility.