Spring Data

Spring Data helps you access and manipulate data in databases without writing tons of code.

Key Features:

• Repository Abstraction: You define an interface, and Spring Data auto-generates the implementation.
• Query Methods: Write queries by just naming your methods (like findByUsername()).
• Support for Many Data Stores:
  • Relational (JPA/Hibernate, JDBC)
  • NoSQL (MongoDB, Neo4j, Redis, Cassandra, etc.)
  • Pagination and Sorting
  • Custom Queries using JPQL, native SQL, or annotations

Repository

Data Access Object level. Interface remains constant independent of the DB behind it.

Repository (Marker-Interface) -> CRUDRepository -> PagingAndSortingRepository

Derived Queries

Queries generated by Spring Data based on the signature.

Methods only need to be defined in the interface. No implementation is required.

Examples

• findByFirstNameAndLastName(String name, String lastname) -> And queries
• findByFirstNameOrderByCreated(String name) -> Ordering
• deleteByName(String name) -> Deletion
• findByAgeGreaterThan -> Less than, greater than, etc
• CountBy -> Results as long
• readBy
• getBy
• queryBy
• findFirst -> returns first entry

AND-OR

Any And, Or Keywords

findByFirstNameAndLastName

EQUALS-IS-NOT

List<Session> findBySessionLengthNot(Integer length);

LIKE- NOT LIKE

Placeholder: %

List<Session> findBySessionNameNotLike(String name);

STARTING/ENDING WITH – CONTAINING

List<Session> findBySessionNameStartingWith(String name);

LESS THAN – GREATER THAN

List<Session> findBySessionLengthLessThan(Integer length);

BEFORE – AFTER – BETWEEN

For Date/Time-Queries

TRUE – FALSE

For boolean fields

List<TicketType> findByIncludesWorkshopTrue();

NULL – NOT NULL

Null, isNull, notNull, isNotNull

List <Speaker> findBySpeakerPhotoNull();

IN – NOT IN

...in(Collection<Daten>)

List <Speaker> findByCompanyIn(List<String> companies);

IGNORE CASE

List<Speaker> findCompanyIgnoreCase(String company);

ORDER BY

List<Speaker> findByLastNameOrderByFirstNameAsc(String lastName);

FIRST – TOP – DISTINCT

findTop5ByFirstName

Paging and Sorting

Iterable<T> findAll(Sort sort);
Page<T> findAll(Pageable pageable);

Or add paging and sorting as parameters to the derived queries.

final Page<Flight> page=flightRepository.findByOrigin("London",PageRequest.of(0,5,Sort.by(Sort.Order.desc("destination"))));

or

@Query("select * from Session s where s.sessionName like %:name")
Page<Session> getSessionWithName(@Param("name") String name, Pageable page);

Custom Module

Extend the repository with custom implementation

• Create a new interface
• Implement the interface
• Existing interface now also extends the CustomRepository interface

public interface DeleteByOriginRepository {
    void deleteByOrigin(String origin);
}

public class DeleteByOriginRepositoryImpl implements DeleteByOriginRepository{
    private final EntityManager entityManager;

    public DeleteByOriginRepositoryImpl(EntityManager entityManager){
        this.entityManager=entityManager;
    }

    @Override
    public void deleteByOrigin(String origin) {
        entityManager.createNativeQuery("DELETE from flight where origin =?").setParameter(1, origin).executeUpdate();
    }
}

Extend existing repository with new functionality

public interface FlightRepository extends PagingAndSortingRepository<Flight, Long>, DeleteByOriginRepository{
    List<Flight> findByOrigin(String london);

    List<Flight> findByOriginAndDestination(String london, String paris);

    List<Flight> findByOriginIn(String ... origins);

    List<Flight> findByOriginIgnoreCase(String origin);

    Page<Flight> findByOrigin(String origin, Pageable pageRequest);
}

Transactions

@Transactional – Annotation to work within a transaction. Reduces boilerplate code, more stable, DB independent…

Tests

Annotate with @SpringBootTest

Spring Data JPA

• Extends JPA • Simplifies the data layer • JpaRepositories • Query DSL • Data tier (sorting, paging, etc.) • Optional. Can easily be bypassed if necessary

Configuration

Pom.xml

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

<!-- Dependency for Postgres JDBC driver -->
<dependency>
   <groupId>org.postgresql</groupId>
   <artifactId>postgresql</artifactId>
   <scope>runtime</scope>
</dependency>

Application.properties
spring.datasource.url=jdbc:postgresql:conference_app
spring.datasource.username=
spring.datasource.password=
spring.jpa.database-platform=org.hibernate.dialect.PostgreSQLDialect
spring.jpa.hibernate.ddl-auto=none

spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true
spring.jpa.show-sql=true

Repository

public interface SpeakerJpaRepository extends JpaRepository<Speaker,Long> {
}

Query-Annotation

For custom queries. Add method with @Query annotation to repository.

@Query("Select tp from TicketPrice tp where tp.basePrice < ?1 "+
        "and tp.ticketType.includesWorkshop = true"
        )
List<TicketPrice> getTicketsUnderPriceWithWorkshops(BigDecimal maxPrice);

?1 First parameter is replaced with parameter of the method.

Named Parameter

Instead of numbered parameters, parameter names can be used.

@Query("Select tp from TicketPrice tp where tp.basePrice < :maxprice "+
        "and tp.ticketType.includesWorkshop = true"
        )
List<TicketPrice> getTicketsUnderPriceWithWorkshops(@Param(“maxprice”) BigDecimal maxPrice);

Enhanced JPQL Syntax

“… where s.sessionName like %?1” Platzhalter ‘%’ kann hinzugefügt werden

Native SQL Query

@Query(value=“select \* from sessions s where s.session_name= ?0”, nativeQuery = true)
List<Session> getSessionsWithName(String name);

Modifiable Queries

@Modifying
@Query("update Session s set s.sessionName = ?1")
int updateSessionName(String name);

NamedQueries

Named Queries are predefined JPQL (Java Persistence Query Language) queries and are validated at the start of the app They are located on the entity, repository or as named attribute by the query annotation

@Entity
@NamedQuery(
    name = "User.findByEmail",
    query = "SELECT u FROM User u WHERE u.email = :email"
)
public class User

NamedNativeQuery

@Entity
@NamedNativeQuery(
    name = "User.findByEmail",
    query = "SELECT * FROM users WHERE email = ?",
    resultClass = User.class
)
public class User

Query priority

1. @Query-Annotation
2. Named/NativeNamed-Queries
3. Query-DSL Naming

Auditing

Annotation of entity properties

• @CreatedBy
• @LastModifiedBy
• @CreatedDate (automatically defined)
• @LastModifiedDate (automatically defined)

Locking

@Version-Annotation in Entity
@Version
private int version

@Lock(LockModeType.PESSIMISIC_WRITE)
List<Model> findByAttributeName(String name)