Spring data rest sorting fields with underscores

It is unclear whether you can do this in some Spring Data Rest specific way however you should be able to handle it by means of a standard Servlet filter which would look something like the below:

public class SortParameterConversionFilter extends GenericFilterBean {

    // as we are extending Spring's GenericFilterBean
    // you can then *possibly* inject the RepositoryRestConfiguration
    // and use  RepositoryRestConfiguration#getSortParamName
    // to avoid hard coding
    private static final String SORT_PARAM_KEY = "sort";

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;

        if (shouldApply(request)) {
            chain.doFilter(new CollectionResourceRequestWrapper(request), res);
        } else {
            chain.doFilter(req, res);
        }
    }

    /**
     * 
     * @param request
     * @return True if this filter should be applied for this request, otherwise
     *         false.
     */
    protected boolean shouldApply(HttpServletRequest request) {
        return request.getServletPath().matches("some-pattern");
    }

    /**
     * HttpServletRequestWrapper implementation which allows us to wrap and
     * modify the incoming request.
     *
     */
    public class CollectionResourceRequestWrapper extends HttpServletRequestWrapper {

        public ResourceRequestWrapper(HttpServletRequest request) {
            super(request);
        }

        @Override
        public String getParameter(final String name) {
            if (name.equals(SORT_PARAM_KEY)) {
                String [] parts = super.getParameter(SORT_PARAM_KEY).split(",");
                StringBuilder builder = new StringBuilder();

                int index = 0;

                for (String part : parts) {
                    // using some mechanism of you choosing
                    // convert from underscore to camelCase
                    // Using the Guava library for example
                    String convertedPart = CaseFormat.LOWER_UNDERSCORE.to(
                         CaseFormat.LOWER_CAMEL, part);
                    ++index;
                    builder.append(convertedPart).append(index < parts.length ? "," : "");
                }

                return builder.toString();
            }

            return super.getParameter(name);
        }
    }
}

In situations, where in

• all field names use Camel Casing in the Entity model
• all entity fields have mapped JsonProperty names which use Snake Casing or have "spring.jackson.property-naming-strategy=SNAKE_CASE" enabled in configuration
• Have very few (2/3) JsonProperty names with underscores and those are used in sort order list
• Do not have multiple other entities facing same issue cause their JsonProperty names with underscores are not used in sort order

Then below code could be used as quick fix with not much impact on perf

 @Override
public Page< <YourEntity> > retrieveSortedList(Pageable pageable) {
Sort sortConditions = pageable.getSort();
         if (!sortConditions.isEmpty()) {
             List<Sort.Order> orderList = sortConditions.stream().toList();
             String curatedFieldName = "";
             List<Sort.Order> sortOrderList = new ArrayList<>();
             for (Sort.Order sortOrderObj : orderList) {
                 if (sortOrderObj.getProperty().contains("_")) {
                     String[] fieldParts = sortOrderObj.getProperty().split("_");
                     curatedFieldName = fieldParts[0];
                     for (int i = 1; i < fieldParts.length; i++) {
                         curatedFieldName += StringUtils.capitalize(fieldParts[i]);
                     }
                     Sort.Direction sortDirection = sortOrderObj.getDirection();
                     sortOrderList.add(new Sort.Order(sortDirection, curatedFieldName));
                 }
             }
             Sort sort = Sort.by(sortOrderList);
             Pageable modifiedPageable = PageRequest.of(pageable.getPageNumber(),
                     pageable.getPageSize(), sort);
             return <YourEntity>Repository.findAll(modifiedPageable);
         }