What is Dirty Checking? Dirty Checking is a mechanism in JPA (Java Persistence API) that automatically detects changes made to an entity and propagates those changes to the database. With Dirty Checking, developers can modify the state of an object without having to explicitly write database update queries. It’s important to note that Dirty Checking only applies to entities managed by the Persistence Context. How Dirty Checking Works Entity Management: Entities are managed by an EntityManager. The Persistence Context stores the initial state of the entities. Change Detection: Before a transaction is committed, JPA compares the current state of an entity with its initial state. Applying Changes: If any changes are detected, JPA automatically generates and executes database update queries. When the transaction is committed, the changes are propagated to the database. Example 1 2 3 4 5 6 7 8 9 10 11 12 13 // Saving the entity Member member = new Member("Alice"); memberRepository.save(member); // Retrieving the entity Member findMember = memberRepository.findById(member.getId()).get(); // Modifying the entity findMember.setName("Bob"); // Change detection // Dirty Checking kicks in and automatically generates and executes a database update query. // UPDATE member SET name = 'Bob' WHERE id = 1; Advantages Convenience: Developers only need to modify the state of the object, without having to write database update queries. Consistency: Data consistency is maintained as changes are automatically propagated to the database. Productivity: It improves productivity as developers can focus on business logic.

What is the N+1 Problem? The N+1 problem is a common performance issue in Object-Relational Mapping (ORM) where N additional queries are executed to retrieve associated entities for each associated entity when querying. As a result, the number of queries becomes N+1. A high number of queries can lead to increased communication with the database and can result in degraded performance. Therefore, the N+1 problem is a concern that requires attention when optimizing performance. ...

Lazy Loading What is Lazy Loading Lazy Loading loads the associated entity when you actually use it, also called a delayed loading. Features It fetches associated data when it is actually being used, not immediately. It is used to optimize performance and to reduce memory usage. It reduces the initial loading time when there are many associated entities. Example 1 2 @OneToMany(fetch = FetchType.LAZY) private List<Order> orders; Advantages Reduces initial loading time. Can reduce memory usage when there are many associated entities. Disadvantages May cause performance degradation as it fires queries every time a part of the associated entity is used. Eager Loading What is Eager Loading Eager Loading is a way to load the associated entity together when the entity is fetched, it is also called an immediate loading. ...

Entity Lifecycle In JPA (Java Persistence API), the entity lifecycle refers to the process from when an entity is created until it is destroyed. 4 States of Entity Lifecycle New/Transient: A new entity is created, but it is not yet managed by an EntityManager. It is not stored in the database and is not managed by the persistence context. Entities created with the new keyword are in the transient state. Managed: ...

EntityManager manages the lifecycle of an entity and performs all operations associated with the entity. EntityManager Meaning An entity manager manages the lifecycle of an entity and performs all operations associated with the entity. The entity manager performs operations such as storing an entity in a database or reading an entity from a database. Key Features The key features of an entity manager are as follows: Persist: Stores an entity in a database. Query: Reads an entity from a database. Update: Modifies an entity stored in a database. Delete: Removes an entity from a database. Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 @Repository public class UserRepository { @PersistenceContext private EntityManager em; public void save(User user) { em.persist(user); } public User findById(Long id) { return em.find(User.class, id); } public void update(User user) { em.merge(user); } public void delete(User user) { em.remove(user); } } The entity manager can be injected using the @PersistenceContext annotation. The entity manager can be used to perform operations such as saving, querying, modifying, and deleting entities. The entity manager operates in a transaction unit, and the entity manager is automatically closed when the transaction ends. ...