code: @Override
      public final SourceDocument findByFileAndString(
              final String filename, final String string) {
          final Query searchQuery = new Query(Criteria.where("string").is(string)
                  .and("filename").is(filename));
          final SourceDocument sourceDocument =
                  mongoTemplate.findOne(searchQuery, SourceDocumentMongo.class);
          if (sourceDocument == null) {
              return null;
          }
          final Source source =
                  (Source) toObjConverter.createGedObject(null, sourceDocument);
          sourceDocument.setGedObject(source);
          return sourceDocument;
      }
docs: {@inheritDoc}