This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Data JPA 3.4.0!spring-doc.cn

Persisting Entities

This section describes how to persist (save) entities with Spring Data JPA.spring-doc.cn

Saving Entities

Saving an entity can be performed with the CrudRepository.save(…) method. It persists or merges the given entity by using the underlying JPA EntityManager. If the entity has not yet been persisted, Spring Data JPA saves the entity with a call to the entityManager.persist(…) method. Otherwise, it calls the entityManager.merge(…) method.spring-doc.cn

Entity State-detection Strategies

Spring Data JPA offers the following strategies to detect whether an entity is new or not:spring-doc.cn

  1. Version-Property and Id-Property inspection (default): By default Spring Data JPA inspects first if there is a Version-property of non-primitive type. If there is, the entity is considered new if the value of that property is null. Without such a Version-property Spring Data JPA inspects the identifier property of the given entity. If the identifier property is null, then the entity is assumed to be new. Otherwise, it is assumed to be not new.spring-doc.cn

  2. Implementing Persistable: If an entity implements Persistable, Spring Data JPA delegates the new detection to the isNew(…) method of the entity. See the JavaDoc for details.spring-doc.cn

  3. Implementing EntityInformation: You can customize the EntityInformation abstraction used in the SimpleJpaRepository implementation by creating a subclass of JpaRepositoryFactory and overriding the getEntityInformation(…) method accordingly. You then have to register the custom implementation of JpaRepositoryFactory as a Spring bean. Note that this should be rarely necessary. See the JavaDoc for details.spring-doc.cn

Option 1 is not an option for entities that use manually assigned identifiers and no version attribute as with those the identifier will always be non-null. A common pattern in that scenario is to use a common base class with a transient flag defaulting to indicate a new instance and using JPA lifecycle callbacks to flip that flag on persistence operations:spring-doc.cn

Example 1. A base class for entities with manually assigned identifiers
@MappedSuperclass
public abstract class AbstractEntity<ID> implements Persistable<ID> {

  @Transient
  private boolean isNew = true; (1)

  @Override
  public boolean isNew() {
    return isNew; (2)
  }

  @PrePersist (3)
  @PostLoad
  void markNotNew() {
    this.isNew = false;
  }

  // More code…
}
1 Declare a flag to hold the new state. Transient so that it’s not persisted to the database.
2 Return the flag in the implementation of Persistable.isNew() so that Spring Data repositories know whether to call EntityManager.persist() or ….merge().
3 Declare a method using JPA entity callbacks so that the flag is switched to indicate an existing entity after a repository call to save(…) or an instance creation by the persistence provider.