A brief introduction to Hibernate

Hibernate is an ORM (Object-Relational Mapping) tool widely used in Java projects to map objects from an application to tables in a relational database.
ORM is a tool that facilitates the mapping between classes in a project and entities in a database.
By using a framework like Hibernate, the developer is able to focus on developing the domain instead of worrying about the details of persistence.

The main features of Hibernate are:
1. Transparency in data access: Hibernate allows developers to write Java code that focuses only on objects and not on persistence details
2. Transaction support: Hibernate offers integrated transactional control, facilitating integration with different transaction managers. This ensures that data read and write operations are performed in a way that data integrity is guaranteed.
3. Inheritance control: Hibernate allows you to flexibly map inheritance between classes to the database. There are different inheritance mapping strategies such as:
Single Table Strategy: A single table for all classes in the hierarchy.
Joined Table Strategy: A table for each concrete class.
Table per Class Strategy: A table for each class.
4. Lazy Loading: Hibernate supports the concept of lazy loading, where data collections and associations are loaded only when necessary, saving memory resources.
5. Validation mechanisms: Hibernate integrates with Bean Validation, allowing you to define validation rules for an entity's fields directly in the class annotations.

Hibernate is one of several implementations of JPA which is a standard specification that defines how the ORM should be implemented in Java.
This framework brings several benefits such as reducing SQL and JDBC code because Hibernate itself automatically generates and executes queries. It is also compatible with a number of relational databases like MySQL, PostgreSQL, MariaDB, etc. The use of caching and the control of well-defined transactions help to optimize application performance.
However, there are disadvantages to using Hibernate as its learning curve, although its simplest operations are the majority when we start to implement caching, inheritance mapping and distributed transactions we may face difficulties in understanding at first. The abstraction offered by Hibernate can also add overhead in certain situations, especially when highly optimized queries are required.

Below we can see an example with a class Product and below an explanation of some of the JPA annotations that are implemented by Hibernate.

`@Entity
@Table(name = "product")
public class Product {

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE)
private BigInteger id;

@Column(name = "nome_produto", nullable = false)
private String nome;

@Column(name = "descricao_produto")
private String descricao;

@Column(name = "preco_produto", nullable = false)
private BigDecimal preco;

// Getter e Setters

}`

1. @Entity
   The @Entity annotation indicates that the Product class is a JPA entity. This means it will be mapped to a table in the database. Each instance of the Product class corresponds to a row in this table.
   The class must have a field with the @id annotation to indicate the unique identifier (primary key) of the entity in the database.

2. @Table(name = "product")
   The @Table annotation specifies the name of the table in the database to which this entity will be mapped. In the example, name = "product" defines that the table associated with the Product entity will be called "product". If the @Table annotation were not provided, the table name would by default be the class name.

3. @id
   The @id annotation is used to mark the id field as the entity's primary key. In the database, this field will be used as the unique identifier for each instance of the Product entity.

4. @GeneratedValue(strategy = GenerationType.SEQUENCE)
   The @GeneratedValue annotation indicates that the value of the id field will be generated automatically. The strategy = GenerationType.SEQUENCE property specifies that Hibernate should use a sequence to generate the primary key values ​​in the database.
   There are other strategies for generating primary keys, such as:
   AUTO: Delegates the choice of strategy to the persistence provider (in this case, Hibernate).
   IDENTITY: Uses an identity column from the database, which generates the value automatically during insertion.
   TABLE: Uses a specific table to store the primary keys.

5. @Column(name = "product_name", nullable = false)
   @Column 注解将类名字段映射到数据库中相应的列。在示例中，该列将被称为“product_name”。
   nullable = false 参数表示该列在数据库中不能为空。换句话说，名称字段必须有一个值。

Hibernate 是一个强大而灵活的工具，用于在 Java 应用程序中操作数据，无需手动编写 SQL。它通过抽象数据库对象和表之间的映射来促进复杂应用程序的开发，并且与 JPA 规范兼容，它提供了标准化的 API，并且可以使用高级功能。

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