SpringData JPA ScrollAPI

Giriş

ScrollAPI aslında Spring Data Commons ile geliyor. SpringData JPA bu bağımlılığı getirdiği için bir şey yapmaya gerek yok

Offset-based scrolling

OffsetScrollPosition  veya WindowIterator sınıfı ile kullanılır. Açıklaması şöyle

Offset scrolling works like pagination, which returns expected results by skipping a certain number of records from a large result. While we only see a portion of the requested results, the server needs to build the full result, which causes additional load.

Örnek

Şöyle  yaparız. Ben sadece bazı açıklamalar ekledim. Window sınıfı offsetleri takip ediyor. Kullanım olarak Window sınıfı Iterator gibi. Window.hasNext() çağrısı yapmak lazım

public List<BookReview> getBooksUsingOffset(String rating) {
  // To keep track of the position in the result set.
  OffsetScrollPosition offset = ScrollPosition.offset();

  // Retrieves the first 5 books with the specified rating
  Window<BookReview> bookReviews = bookRepository.findFirst5ByBookRating(rating, offset);
  List<BookReview> bookReviewsResult = new ArrayList<>();
  do {
    // Adds each BookReview to result
    bookReviews.forEach(bookReviewsResult::add);
    // Retrieves the next batch of 5 books with the specified rating
    bookReviews = bookRepository
      .findFirst5ByBookRating(
        rating, 
        (OffsetScrollPosition) bookReviews.positionAt(bookReviews.size() - 1));
  } while (!bookReviews.isEmpty() && bookReviews.hasNext());

   return bookReviewsResult;
}

Örnek

Şöyle  yaparız.   WindowIterator + OffsetScrollPosition  kullanılır. Window.hasNext() çağrısı yapmaya gerek yok

public List<BookReview> getBooksUsingOffSetFilteringAndWindowIterator(String rating) {
  WindowIterator<BookReview> bookReviews = WindowIterator.of(position -> 
    bookRepository
      .findFirst5ByBookRating("3.5", (OffsetScrollPosition) position))
      .startingAt(ScrollPosition.offset());

  List<BookReview> bookReviewsResult = new ArrayList<>();
  bookReviews.forEachRemaining(bookReviewsResult::add);

  return bookReviewsResult;
}

Keyset-Filtering

Açıklaması şöyle. WindowIterator + KeysetScrollPosition  kullanılır

Keyset filtering helps the retrieval of a subset of results using the built-in capabilities of the database aiming to reduce the computation and IO requirements for individual queries.

The database only needs to construct smaller results from the given keyset position without materializing a large full result

Örnek

Şöyle yaparız

public List<BookReview> getBooksUsingKeySetFiltering(String rating) {
  WindowIterator<BookReview> bookReviews = WindowIterator.of(position -> 
    bookRepository
      .findFirst5ByBookRating(rating, (KeysetScrollPosition) position))
      .startingAt(ScrollPosition.keyset());
    
  List<BookReview> bookReviewsResult = new ArrayList<>();
  bookReviews.forEachRemaining(bookReviewsResult::add);

  return bookReviewsResult;
}