Kotlin functional wrapper for Spring-data repository's pagination

RepositoryPaginater.kt

 /**
   * Extension function for Spring-Data's CrudRepository providing a convenient wrapper to handle pagination in a Kotlin-idiomatic way.
   * 
   * Creates a Sequence using Page and Pageable to iterate calls to a paginated Spring-Data function call.  
   * 
   * Example usage:
   * 
   *    myPagingAndSortingRepository.paginate(50) { pageable ->
   *       // directly call any function on the repository that returns a Page
   *       findAll(pageable)
   *    }
   *    // Sequence<Page<T>> - the rows of data are accessible at page.content
   *    .flatMap { it.content }
   *    // now you have Sequence<T>
   *    .forEach { record -> 
   *       //operate on each record
   *    }
   * 
   */
  fun <T, ID, R: CrudRepository<T, ID>> R.paginate(pageSize: Int, query : R.(Pageable) -> Page<T>) : Sequence<Page<T>> {
      return generateSequence ({ query(PageRequest.of(0, pageSize))}, { prevPage : Page<T> ->
          logger.info { "paginater: in sequence generator, prevPage: '$prevPage'" }
          if (prevPage.hasNext()) {
              logger.info { "paginater: more data (totalElements: ${prevPage.totalElements}, totalPages: ${prevPage.totalPages}), getting next pageable..." }
              query(prevPage.nextPageable())
          } else {
              logger.info { "paginater: no more data, ending sequence after ${prevPage.totalElements} items." }
              null
          }
      })
  }

No need for the R type parameter. You can remove the parameter and replace all the other Rs with CrudRepository<T, ID>

Oh yeah. Thanks!

@jbotuck actually that doesn't work the same... R doesn't represent precisely a CrudRepository, it represents 'any class that extends CrudRepository'. So in a usage example where MyCrudRepository extends CrudRepository and adds some functions, without R the query function's receiver is just a CrudRepository and not MyCrudRepository so I cannot call the extra MyCrudRepository functions directly from the query function.