Springdata JPA repository findAllByXXX() return null instead of an empty list

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06-10-2024

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Spring Data JPA's findAllByXXX() Returning Null: Why and How to Fix It

Problem: You're using Spring Data JPA's findAllByXXX() method in your repository to fetch entities based on certain criteria. Instead of getting an empty list when no results are found, the method returns null. This can lead to unexpected errors and make your code less robust.

Rephrased: Imagine you're looking for a specific type of book in a library. You ask the librarian for all books by a particular author, but they tell you there are none. It's like the librarian returned "nothing" instead of an empty list of books. This is the same problem findAllByXXX() faces in Spring Data JPA when no entities match the search criteria.

Scenario:

@Repository
public interface BookRepository extends JpaRepository<Book, Long> {

    List<Book> findAllByAuthor(String author);
}

@Service
public class BookService {

    @Autowired
    private BookRepository bookRepository;

    public List<Book> findBooksByAuthor(String author) {
        return bookRepository.findAllByAuthor(author);
    }
}

The Issue: Spring Data JPA, by default, returns null when no entities match the query in findAllByXXX(). This behavior is inconsistent with the expected behavior of returning an empty list.

Analysis:

The root cause lies in how Spring Data JPA handles query results. When no entities are found, the findAllByXXX() method doesn't actually execute a query to retrieve an empty list. Instead, it relies on the database's response, which often returns null for empty result sets. This behavior is not specific to findAllByXXX() but applies to any custom query method that doesn't explicitly return an empty list.

Solutions:

1. Explicitly Return an Empty List: You can override the default behavior by defining a method that explicitly returns an empty list when no results are found.

   @Repository
   public interface BookRepository extends JpaRepository<Book, Long> {
       List<Book> findAllByAuthor(String author);
   
       default List<Book> findAllByAuthorOrDefault(String author) {
           List<Book> books = findAllByAuthor(author);
           return books != null ? books : new ArrayList<>();
       }
   }
   

   This approach ensures consistency by always returning a List object, even when empty.

2. Use Optional: Leverage Java's Optional class to handle potential null values.

   @Repository
   public interface BookRepository extends JpaRepository<Book, Long> {
       Optional<List<Book>> findAllByAuthor(String author);
   }
   
   @Service
   public class BookService {
   
       @Autowired
       private BookRepository bookRepository;
   
       public List<Book> findBooksByAuthor(String author) {
           return bookRepository.findAllByAuthor(author).orElse(new ArrayList<>());
       }
   }
   

   This solution allows you to handle the absence of results gracefully using Optional.orElse().

3. Configure Spring Data JPA: While not recommended, you can configure Spring Data JPA to always return an empty list for empty result sets. This requires setting the hibernate.query.result_set_empty_rows_as_null property to false in your application's configuration.

   Caveat: This approach might have unintended consequences and impact other queries. It's generally better to handle null values directly within your code.

Benefits of Fixing the Problem:

• Improved Code Robustness: Avoiding null values makes your code less prone to NullPointerExceptions and more resilient to unexpected scenarios.
• Clarity and Readability: Explicitly returning an empty list or using Optional makes your code easier to understand and maintain.
• Consistency: Ensuring consistent behavior for both empty and non-empty results sets improves the predictability of your code.

Conclusion:

While Spring Data JPA's findAllByXXX() method can return null when no entities are found, it's best practice to address this by explicitly returning an empty list or using Optional. This will make your code more robust, readable, and consistent, ultimately leading to a better developer experience.