How do I update an entity using spring-data-jpa?

Mastering the save() Method

Whenever you call repository.save(entity), Spring Data JPA works its magic to apply your changes based on the presence of an ID. When the crafty ID is present, save() leverage merge(), orchestrating an update operation. But if the elusive ID is missing, it draws upon persist() to conduct an insert operation.

JPA's Unit of Work - The Master Puppeteer

The Unit of Work pattern is JPA's right hand. It ensures that any change within a transaction is applied as a package deal when the transaction commits. This reliable pattern makes Spring Data JPA's entity management a breeze.

Transactions - Marshalling the Troops

Strike the drumbeat of efficiency by always running update operations within a transactional context. Spring's @Transactional annotation is your loyal herald, delineating the boundaries, and sparing you the manual persistence operations, leaving just save() doing the heavy lifting.

Custom Update Queries, Anyone?

Even JPA's dirty checking has its limits, or maybe you need an eccentric update query. Fret not! By annotating a method in your repository interface with @Query and @Modifying, you can conduct custom operations like a pro.

@Modifying
@Query("update YourEntity y set y.field = :value where y.id = :id") // Bestow some new value
int updateTheField(@Param("value") FieldType newValue, @Param("id") Long id); // New ID, who's this?


Executing this method gives you an int showing the headcount of affected records.

The Need for Speed: Performance and Efficiency

For optimum performance, avoid unnecessary joins or eager fetching that tend to bloat the update operation's cost. If the update logic turns more complex than a Rubik's cube, encapsulate transaction boundaries in a service layer and let your repository snugly focus on data access.