Batch deletes (orphanRemoval = true)

Author: AnghelLeonard

HibernateSpringBootBatchDeleteOrphanRemoval/pom.xml

@@ -7,7 +7,7 @@
     <artifactId>HibernateSpringBootBatchDeleteOrphanRemoval</artifactId>
     <version>1.0</version>
     <packaging>jar</packaging>
-
+ 
     <name>HibernateSpringBootBatchDeleteOrphanRemoval</name>
     <description>JPA project for Spring Boot</description>
 

HibernateSpringBootBatchDeleteOrphanRemoval/src/main/java/com/bookstore/entity/Author.java

@@ -28,7 +28,7 @@ public class Author implements Serializable {
     @Version
     private short version;
 
-    @OneToMany(cascade = {CascadeType.ALL},
+    @OneToMany(cascade = CascadeType.ALL,
             mappedBy = "author", orphanRemoval = true)
     private List<Book> books = new ArrayList<>();
 

HibernateSpringBootBatchDeleteOrphanRemoval/src/main/java/com/bookstore/repository/AuthorRepository.java

@@ -8,13 +8,11 @@
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.jpa.repository.QueryHints;
 import org.springframework.stereotype.Repository;
-import org.springframework.transaction.annotation.Transactional;
 
 @Repository
 public interface AuthorRepository extends JpaRepository<Author, Long> {
 
-    @Transactional(readOnly = true)
     @QueryHints(value = @QueryHint(name = HINT_PASS_DISTINCT_THROUGH, value = "false"))
-    @Query(value = "SELECT DISTINCT a FROM Author a JOIN FETCH a.books b")
-    List<Author> fetchAllAuthorsAndBooks();
+    @Query(value = "SELECT DISTINCT a FROM Author a JOIN FETCH a.books b WHERE a.age < ?1")
+    List<Author> fetchAuthorsAndBooks(int age);
 }

HibernateSpringBootBatchDeleteOrphanRemoval/src/main/java/com/bookstore/service/BookstoreService.java

@@ -29,7 +29,7 @@ public void batchAuthorsAndBooks() {
             Author author = new Author();
             author.setName("Name_" + i);
             author.setGenre("Genre_" + i);
-            author.setAge(18 + i);
+            author.setAge((int) ((Math.random() + 0.1) * 100));
 
             for (int j = 0; j < 5; j++) {
                 Book book = new Book();
@@ -45,39 +45,42 @@ public void batchAuthorsAndBooks() {
         authorRepository.saveAll(authors);
     }
 
-    // explicitly delete all records from each table (ignores orphanRemoval = true)
+    // explicitly delete all records from each table
     @Transactional
     public void deleteAuthorsAndBooksViaDeleteAllInBatch() {
         authorRepository.deleteAllInBatch();
         bookRepository.deleteAllInBatch();
     }
 
-    // explicitly delete all records from each table (ignores orphanRemoval = true)
+    // explicitly delete all records from each table
     @Transactional
     public void deleteAuthorsAndBooksViaDeleteInBatch() {
-        List<Author> authors = authorRepository.fetchAllAuthorsAndBooks();
+        List<Author> authors = authorRepository.fetchAuthorsAndBooks(60);
 
         authorRepository.deleteInBatch(authors);
         authors.forEach(a -> bookRepository.deleteInBatch(a.getBooks()));
     }
 
     // good if you need to delete in a classical batch approach
-    // (uses orphanRemoval = true, but generates 20 batches because DELETE statements are not sorted at all)
+    // deletes are cascaded by CascadeType.REMOVE and batched as well
+    // the DELETE statements are not sorted at all and this causes more batches than needed for this job
     @Transactional
-    public void deleteAuthorsAndBooksViaDeleteAll() {        
-        authorRepository.deleteAll(); // for a collection of certain Authors use deleteAll(Iterable<? extends T> entities)       
+    public void deleteAuthorsAndBooksViaDeleteAll() {
+        List<Author> authors = authorRepository.fetchAuthorsAndBooks(60);
+        
+        authorRepository.deleteAll(authors); // for deleting all Authors use deleteAll()       
     }
 
     // good if you need to delete in a classical batch approach
-    // (uses orphanRemoval = true, and generates only 3 batches)
+    // (uses orphanRemoval = true, and optimize the number of batches)
     @Transactional
     public void deleteAuthorsAndBooksViaDelete() {
 
-        List<Author> authors = authorRepository.fetchAllAuthorsAndBooks();
-        
+        List<Author> authors = authorRepository.fetchAuthorsAndBooks(60);
+
         authors.forEach(Author::removeBooks);
         authorRepository.flush();
 
-        authors.forEach(authorRepository::delete); // or, authorRepository.deleteAll();
+        authors.forEach(authorRepository::delete); // or, authorRepository.deleteAll(authors);
     }
 }