How to sort PageRequest on String as numeric value

Question

I currently have a system in place which can filter and sort records in the database and return them as a Paged object. One of the lines is like this:

final          


        

Answer 1

I think you could try the Spring Data JpaSort class which allows function calls.

As stated in the documentation you will have something like :

@Query("select u from User u where u.lastname like ?1%")
  List<User> findByAndSort(String lastname, Sort sort);

repo.findByAndSort("targaryen", JpaSort.unsafe("LENGTH(firstname)"));

You could also use it with a Pageable object.

Answer 2

Assume that you have entity with a String filed and you want to sort it like Long with jpa Pageable.

So you need to do following things:(Remember this only works with Oracle Database)

1. Add a new filed in your entity with Long type
2. for the new filed use @Formula in getter method and evoke to_number()

@Entity
public class testEntity{
         private String oldField;  //Getter and Setter

         private Long newField; //Setter

         @Formula(value = "to_number(oldField)")
         public Long getNewField() {
                return newField;
         } 
 }

3. in your service find sorted filed and change it to the newfiled

 if (Objects.nonNull(pagingRequest.getSort()) && pagingRequest.getSort().getFieldName().equals("oldField")) {
            pagingRequest.getSort().setFieldName("newField");
 }

Answer 3

So basically you need to do two things:

1. Implement custom comparator,
2. Annotate the entity class.

Ad.1.

public class HouseComparator implements Comparator<House> {
    @Override
    public int compare(House h1, House h2) {

        String s1 = h1.getHouseNumber().split("[^0-9]")[0];
        String s2 = h2.getHouseNumber().split("[^0-9]")[0];

        return s1.compareTo(s2);
    }
}

You need to add some better handling of your cases. The above comparator says, that h1 is less than h2 when it begins with a smaller number and vise versa. For this comparator 12A is equal 12B but it's up to you.

Ad.2.

@SortComparator(HouseComparator.class)
List<House> findByHouseNumber(Pageable pageable);