On Wednesday, May 1, 2013 4:39:49 PM UTC-7, Anthony wrote: > > > The first thing to notice here, is that an ORM object-attribute can >> contain NON-SCALAR values - meaning, a link to a list of other objects. >> There is no feature in web2py that generates such an object. >> >> The second thing to notice here, is that the attributes of an ORM object >> usually contain child-objects (plural) that represent fields from a >> different table than the parent-object. Again, there is no feature in >> web2py that can generate such an object. A JOIN operation may return row >> objects, each of which may contain sub-attributes that hold A SINGLE >> field-value >> from a foreign-table, but it is a *scalar-value* - NOT another * >> domain-entity-object* (with it's own attributes, etc.), NOR a SEQUENCE >> of *domain-entity objects* >> > >> ... >> > > The crucial thing to notice here is that an ORM object-attribute can >> contain NON-SCALAR values - meaning, a link to a list of other objects, >> which themselves may contain links to other objects/sequences-of-objects, >> etc. >> > > Although ORM's may do that, such a feature is not unique to the ORM > pattern. In the web2py DAL, for example, in a Row object with a reference > to another table, the reference field is actually a DAL.Reference object, > not a scalar value (it includes the scalar value but also allows access to > related records in the referenced table). >
In this case it does not reference a set of DAL fields. > Similarly, a Row object from a table that is referenced by another table > includes an attribute that is a DAL.LazySet object (also not a scalar), > which allows access to the records in the referencing table that reference > the current Row object. > I did not know that - what form of *Layziness* are we talking about here? Will it generate a query to fill-up the target rows? In any case, it is stil a reference to something the WOULD generate a Rows object - it is not a reference to an already-exising domain-object (which may then have references to othe domain-objects, etc. - all already within memory) object as is in ORMS > The DAL also has list:-type fields, whose values are lists, including > lists of DAL.Reference objects in the case of list:reference fields. > That's interesting, but that is not exactl the same - list-fields need to be supported in the database, but in any case, it is not comparable to being linked to relation ally-stored primary-keys - which would be how it would be implemented in an ORM. Row objects can also include custom methods (i.e., "lazy" virtual fields) > as well as virtual fields, which can contain complex objects. > Relates to the comment I gave you a couple of minutes ago... These are complementary-auxiliary features (with in the web2py-implementation case, have questionable real-world-utility) which while they do go beyond a "simple" value, they are still scalar, as they ultimately result in a reference to a scalar-value - not a reference to a sequence of objects. > > Anthony > > > -- --- You received this message because you are subscribed to the Google Groups "web2py-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to web2py+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
