code: public NumberExpression<Integer> srid() {
          if (srid == null) {
              srid = Expressions.numberOperation(Integer.class, SpatialOps.SRID, mixin);
          }
          return srid;
      }
docs: Returns the Spatial Reference System ID for this geometric object. This will normally be a
  foreign key to an index of reference systems stored in either the same or some other datastore.
  
  @return SRID