#Filtering Entities by conditions in a generic and safe way

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amber inlet
#

I have built the following pagination component that would allow me to return data to be filled in a table, in which the table can filter each field in frontend.

tribal gardenBOT
#

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amber inlet
#

The following is my base class

public class BaseRepository<T, ID extends Serializable>
    extends SimpleJpaRepository<T, ID> implements IBaseRepository<T, ID> {
  public final Class<T> entityClass;

  public BaseRepository(
      JpaEntityInformation<T, ?> entityInformation,
      EntityManager entityManager
  ) {
    super(
        entityInformation,
        entityManager
    );
    this.entityClass = entityInformation.getJavaType();
  }

  public Page<T> findAllWithFilters(
      PaginationParams paginationParams,
      Optional<Specification<T>> extraSpecifications
  ) {
    Map<String, String> originalFilters = paginationParams.getFilters();
    Map<String, String> mappedFilters = new HashMap<>();

    for (var entry : originalFilters.entrySet()) {
      String key = entry.getKey();
      String value = entry.getValue();
      var splits = key.split("_");
      if (splits.length != 2)
        continue;

      String dtoField = splits[0];
      String operation = splits[1];

      String entityField = PaginationFieldMapper.resolveField(
          entityClass,
          dtoField
      );
      mappedFilters.put(
          entityField + "_" + operation,
          value
      );
    }

    Pageable pageable = paginationParams.toPageable();
    return extraSpecifications.map(tSpecification -> findAll(
                                  tSpecification.and(GenericSpecification.buildSpecification(mappedFilters)),
                                  pageable
                              ))
                              .orElseGet(() -> findAll(
                                  GenericSpecification.buildSpecification(mappedFilters),
                                  pageable
                              ));
  }
}
# 
  @Transactional(readOnly = true)
  public BaseResponseEntity<Page<AccountPaginatedDto>> getUsers(
      PaginationParams paginationParams
  ) {
    var results = userRepository.findAllWithFilters(
        paginationParams,
        null
    );
    var mappedResult = results.map((res) -> {
      var dto = new AccountPaginatedDto();
      dto.setUsername(res.getUsername());
      dto.setEmail(res.getEmail());
      dto.setId(String.valueOf(res.getId()));
      dto.setFirstName(res.getFirstname());
      dto.setLastName(res.getLastname());
      return dto;
    });
    return new BaseResponseEntity<>(mappedResult);
  }

as you can see i have added Optional<Specification<T>> extraSpecifications into my method, which the idea is that for example if i want to fetch all users for my table i would fetch all with the filters chosen from frontend + my filters (enabled and not deleted)

coming from C# dotnet, we use Linq, which i can directly add something like

var results = userRepository.findAllWithFilters(
        paginationParams,
        i=> i.isEnabled && !i.isDeleted
);
#

i want to do this in a generic way such that i dont have to build classifications class for each entity.
I want it to be clean and safe so for example i dont want to use strings to tell which property i want to filter

#

I read about jOOQ, QueryDSL but im not sure if that fits what i need, and i want this to be following best practices in java springboot

#

Any feedback would be greatly appreciated ❤️

modern quiver
amber inlet
tribal gardenBOT
# amber inlet thanks a lot i ended up implementing this ^

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