code: private function getFilterForComparingOperator($attribute, IFilter $filter, $operation)
      {
          if ($attribute) {
              switch ($operation['operation']) {
                  case '=':
                      $filter->addFilterRule(new SearchAttribute(
                          $attribute,
                          $operation['value'],
                          $this->getMetaModel()->getAvailableLanguages() ?: array()
                      ));
                      return;
  
                  case '>':
                      $filter->addFilterRule(new GreaterThan(
                          $attribute,
                          $operation['value']
                      ));
                      return;
  
                  case '<':
                      $filter->addFilterRule(new LessThan(
                          $attribute,
                          $operation['value']
                      ));
                      return;
  
                  default:
                      throw new \RuntimeException(
                          'Error processing filter array - unknown operation ' .
                          var_export($operation['operation'], true),
                          1
                      );
              }
          }
  
          $columns = $this->connection->getSchemaManager()->listTableColumns($this->getMetaModel()->getTableName());
          if ($columns[$operation['property']]) {
              // System column?
              $filter->addFilterRule(new SimpleQuery(
                  sprintf(
                      'SELECT id FROM %s WHERE %s %s?',
                      $this->getMetaModel()->getTableName(),
                      $operation['property'],
                      $operation['operation']
                  ),
                  array($operation['value']),
                  'id',
                  $this->connection
              ));
  
              return;
          }
  
          throw new \RuntimeException(
              'Error processing filter array - unknown property ' . var_export($operation['property'], true),
              1
          );
      }
docs: Build the sub query for a comparing operator like =,<,>.
  
  @param IAttribute $attribute The attribute.
  
  @param IFilter    $filter    The filter to add the operations to.
  
  @param array      $operation The operation to convert.
  
  @return void
  
  @throws \RuntimeException When the operation can not be parsed.