Spring Data JPA

Maven Dependency

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

Database Entity

In domain or entity package you can define a Database Entity:

@Entity (1)
public class Book {

    @Id  (2)
    @GeneratedValue (3)
    @UuidGenerator (4)
    @JdbcTypeCode(SqlTypes.CHAR) (5)
    @Column(length = 36, columnDefinition = "varchar(36)", updatable = false, nullable = false) (6)
    private UUID id;

    @Version (7)
    private Integer version;

    @CreationTimestamp (8)
    private LocalDateTime creationDate;

    @UpdateTimestamp (9)
    private LocalDateTime updateDate;

    // Other fields, Constructors, Getters and Setters, toString(), equals(Object obj) and hashCode()

}

1	`@Entity` specifies that the class is a Database Entity.
2	`@Id` specifies the primary key of an Entity.
3	`@GeneratedValue` specifies the generation strategy for the value of primary key. See `🟣 GenerationType` for generation strategies. `AUTO` selects `SEQUENCE`, `TABLE`, or `UUID` based on the Entity identifier type and capabilities of the database.
4	`@UuidGenerator` specifies that an Entity identifier is generated as a UUID type.
5	`@JdbcTypeCode` specifies the JDBC type-code to use for the column mapping.
6	`@Column` specifies the mapped column for a field. If no `@Column` is specified, the default values apply.
7	`@Version` specifies the version field that serves as its optimistic lock value. The version is used to ensure integrity when performing the merge operation and for optimistic concurrency control.
8	`@CreationTimestamp` specifies that the annotated field is a generated creation timestamp. The timestamp is generated just once, when an entity instance is inserted in the database.
9	`@UpdateTimestamp` specifies that the annotated field is a generated update timestamp. The timestamp is regenerated every time an entity instance is updated in the database.

Repository

When we run the application, Spring Data JPA is going to provide us a Repository implementation. It means that we only have to define a Repository interface.

⚪ CrudRepository<T,ID>

Repository for generic CRUD operations on a Repository for a specific type:

T is the domain type the Repository manages,
ID is the type of the id of the Entity the Repository manages.

public interface BookRepository extends CrudRepository<Book, UUID> {}

⚪ ListCrudRepository<T,ID>

Extension to ⚪ CrudRepository<T,ID> returning ⚪ List instead of ⚪ Iterable where applicable.

⚪ PagingAndSortingRepository<T,ID>

Repository fragment to provide methods to retrieve entities using the pagination and sorting abstraction. In many cases this will be combined with ⚪ CrudRepository<T,ID> or similar or with manually added methods to provide CRUD functionality.

⚪ ListPagingAndSortingRepository<T,ID>

Extension to ⚪ PagingAndSortingRepository<T,ID> returning ⚪ List instead of ⚪ Iterable where applicable.

⚪ JpaRepository<T,ID>

JPA specific extension of Repository. Extension to ⚪ ListCrudRepository<T,ID> and ⚪ ListPagingAndSortingRepository<T,ID> which can also Query by Example.