What is an idempotent method in Spring Data?

An idempotent method in Spring Data is a repository method whose repeated execution with the same input parameters guarantees the same final result in the data store.

Idempotency is important in API development and distributed systems to ensure reliability during repeated attempts to perform operations, for example, in case of network errors. Examples of idempotent operations include:

• Reading data (SELECT).
• Updating an existing record (UPDATE), where the new state is determined solely by the request parameters, not the current state.
• Deleting a record (DELETE).

Non-idempotent operations include:

• Creating a new record (INSERT), each execution of which creates a new entity.
• Updating that depends on the current state (e.g., incrementing a counter).

In the context of Spring Data, most methods generated by name (find, get, count), as well as standard JpaRepository methods (findById, findAll, deleteById), are idempotent. The save method can be either idempotent (updating an existing entity) or non-idempotent (creating a new one).

Example:

// Idempotent method
Optional<User> findById(Long id);

// Idempotent method
void deleteById(Long id);

// Can be both idempotent (update) or non-idempotent (create)
<S extends User> S save(S entity);