I have recently written several posts about Kotlin\u2019s delegation. In doing so, I realised a useful way to apply it to Spring Data repositories. Which would allow Spring Data to continue sprinkling some magic while providing a route for customisation. The code shown in this post is in Kotlin, but is still relevant to Java.<\/p>\n
This post uses R2DBC, but the content is generic enough to be applicable to any Spring Data module.<\/p>\n
Reading Asynchronous RDBMS access with Spring Data R2DBC<\/a> and Class delegation in Kotlin<\/a> would be beneficial here if you do not have much background knowledge in these areas.<\/p>\n As a recap. What is the magic that Spring Data provides?<\/p>\n Spring Data allows you to write an interface where you are only required to define the queries that you need. It will then do all the work of creating the implementation and injecting dependencies for you. This looks something like:<\/p>\n Since Spring Data R2DBC is being used, fully inferred queries are not yet fully supported. This is why the query is written out manually.<\/p>\n The downside to this is that it is creating an implementation based on an interface. Therefore, if you want to do any sort of customisation, you will need to create an instance of the interface yourself, inject in its dependencies and implement each query. For example:<\/p>\n Yes, that query code is probably terrible, and I am sure you could do better. You get my point though. The pain of creating this class can be removed by delegating to the repository Spring implemented based on your interface. You can then add all the customisations you need.<\/p>\n In Kotlin, this would look like:<\/p>\n In Java, it is a bit more cumbersome but still easily achievable:<\/p>\n\n\n
\n \n \n @Repository<\/code><\/div>\ninterface<\/code> PersonRepository : R2dbcRepository<Person, Int> {<\/code><\/div>\n <\/code>@Query<\/code>(<\/code>\"SELECT * FROM people WHERE age > $1\"<\/code>)<\/code><\/div>\n <\/code>fun findAllByAgeGreaterThan(age: Int): Flux<Person><\/code><\/div>\n}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n\n\n
\n \n \n class<\/code> PersonRepositoryImpl(<\/code><\/div>\n <\/code>private<\/code> val entity: RelationalEntityInformation<Person, Int>,<\/code><\/div>\n <\/code>private<\/code> val databaseClient: DatabaseClient,<\/code><\/div>\n <\/code>converter: R2dbcConverter,<\/code><\/div>\n <\/code>private<\/code> val accessStrategy: ReactiveDataAccessStrategy<\/code><\/div>\n) : SimpleR2dbcRepository<Person, Int>(entity, databaseClient, converter, accessStrategy),<\/code><\/div>\n <\/code>PersonRepository {<\/code><\/div>\n <\/code>override fun findAllByAgeGreaterThan(age: Int): Flux<Person> {<\/code><\/div>\n <\/code>val mapper: StatementMapper.TypedStatementMapper<Person> =<\/code><\/div>\n <\/code>accessStrategy.statementMapper.forType(entity.javaType)<\/code><\/div>\n <\/code>val selectSpec: StatementMapper.SelectSpec = mapper<\/code><\/div>\n <\/code>.createSelect(entity.tableName)<\/code><\/div>\n <\/code>.withProjection(accessStrategy.getAllColumns(entity.javaType))<\/code><\/div>\n <\/code>.withCriteria(Criteria.where(<\/code>\"age\"<\/code>).greaterThan(age))<\/code><\/div>\n <\/code>val operation: PreparedOperation<*> = mapper.getMappedObject(selectSpec)<\/code><\/div>\n <\/code>return<\/code> databaseClient.execute().sql(operation).`as`(entity.javaType).fetch().all()<\/code><\/div>\n <\/code>}<\/code><\/div>\n}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n\n\n
\n \n \n @Repository<\/code><\/div>\nclass<\/code> DelegatingPersonRepository(<\/code>private<\/code> val delegate: PersonRepository) :<\/code><\/div>\n <\/code>PersonRepository by delegate {<\/code><\/div>\n <\/code>override fun <S : Person> save(objectToSave: S): Mono<S> {<\/code><\/div>\n <\/code>\/\/ override `save` implementation<\/code><\/div>\n <\/code>}<\/code><\/div>\n <\/code>\/\/ any other overrides (kotlin provides delegated implementations)<\/code><\/div>\n}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n\n\n
\n \n \n @Repository<\/code><\/div>\npublic<\/code> class<\/code> DelegatingPersonRepository <\/code>implements<\/code> PersonRepository {<\/code><\/div>\n <\/code>private<\/code> final<\/code> PersonRepository delegate;<\/code><\/div>\n <\/code>public<\/code> DelegatingPersonRepository(PersonRepository delegate) {<\/code><\/div>\n <\/code>this<\/code>.delegate = delegate;<\/code><\/div>\n <\/code>}<\/code><\/div>\n <\/code>@Override<\/code><\/div>\n <\/code>public<\/code> Flux<Person> findAllByAgeGreaterThan(<\/code>int<\/code> age) {<\/code><\/div>\n <\/code>return<\/code> delegate.findAllByAgeGreaterThan(age);<\/code><\/div>\n <\/code>}<\/code><\/div>\n <\/code>@Override<\/code><\/div>\n <\/code>public<\/code> <S <\/code>extends<\/code>