John,
We are often modeling object that are based on Cayenne objects but include
data from several object and when we model relationships we use URLs to
specify how to get related data. And I almost always model bi-directional
(circular) relationships.
Tony
On Thu, Sep 19, 2019 at 11:40 AM John Huss <johnth...@gmail.com> wrote:
> I guess I'm not clear on what you are using the DTO for. If I was using
> DTOs it would be the same class on the server *and* the client (GWT). If
> you're only creating DTOs in order to serialize them to a non-java
> destination that just seems like a waste of effort. I suspect any good
> serialization library should be able to handle customizing the
> serialization of the regular DataObjects themselves without needing another
> layer.
>
> Jackson (JSON) supports using MixIn classes to tweak serialization so that
> your regular cayenne classes are not affected ("polluted") in any way.
>
> I strongly recommend against modeling circular relationships (two way
> relationships) in your cayenne model to avoid headaches with serialization.
> If you avoid circular relationships then you can use MixIns to fairly
> easily trim your object graph to a reasonable size. Jackson also has Views
> which can be used if you need to have more than one representation for a
> class depending on the situation.
>
>
>
>
> On Wed, Sep 18, 2019 at 7:52 AM Tony <t...@giaccone.org> wrote:
>
> > Obviously the complexity of thiscould go off the charts. And you’re right
> > the obvious complex solution would be agrest. I’m thinking of the
> opposite
> > extreme. One DTO object per entity.
> >
> > Double bonus points if the DTO has two methods, entityToDTO and
> > dtoToEntity.
> >
> > Relationship data can be as complicated and varied as use cases but a
> > check box on the entity that created a DTO with just the attributes would
> > certainly make my life easier.
> >
> > Mike Gentry’s idea of using Jackson I personally don’t like. DTO and
> > entity perform two different tasks and I don’t want to intertwine them. I
> > recognize they are awfully close in nature and using Jackson is tempting
> > but we still create DTOs. I’ll have to think on that more.
> >
> > Case by case you have to decide which relationships you should bundle
> back
> > but more and more I like links to fetch related data. Again not always
> > appropriate but if you have DTOs readily made you can bundle them up in
> the
> > payload as well.
> >
> > The other advantage of this is that you could market AGRest as the next
> > step beyond the DTO solution that comes in Cayenne.
> >
> > Edge cases are always where the devil lives. :-) Thankfully we’re here to
> > solve those problems.
> >
> > Tony Giaccone
> >
> > > On Sep 18, 2019, at 2:21 AM, Andrus Adamchik <and...@objectstyle.org>
> > wrote:
> > >
> > > Ignoring serialization mechanics (and even the presence of Cayenne) for
> > a moment, I was always wondering how do people even approach this
> problem.
> > Every persistent object is potentially an entry point to a near-infinite
> > graph of objects coming from DB. So you need to have a set of clear rules
> > of how deep and wide you want to go when you start serializing.
> > >
> > > DTO is one way to define such rules. But unless your rules are very
> > simple ("send the attributes, don't send the relationships"), if you
> start
> > generating DTOs, they will have the same set of relationships. And you'd
> > end up with the same issue as you had with serializing the original
> > DataObjects.
> > >
> > > So what parts of the graph do you need to serialize?
> > >
> > > And if this needs to be flexible, I would probably write a small
> library
> > that allows a user to define a subset of model to serialize, and then
> > applies that "submodel" to DataObjects directly (this is the Agrest.io
> > approach on a smaller scale). But as with any generic solution, this will
> > require a bit of effort, dealing with edge cases, etc.
> > >
> > > Andrus
> > >
> > >
> > >
> > >> On Sep 18, 2019, at 12:29 AM, John Huss <johnth...@gmail.com> wrote:
> > >>
> > >> It's a small effort to create a custom entity template to generate any
> > kind
> > >> of entity class you want, for instance for a DTO. You can copy a lot
> of
> > >> stuff right out of the regular templates if you want.
> > >>
> > >> Then you can use maven or ant to easily regenerate those classes the
> > same
> > >> way CayenneModeler does without having to change the custom template
> > >> selections all the time.
> > >>
> > >>> On Tue, Sep 17, 2019 at 1:49 PM Tony Giaccone <t...@giaccone.org>
> > wrote:
> > >>>
> > >>> So typically I create a Data Transfer Object to return values across
> > the
> > >>> wire that I have fetched and copy attributes from my model object to
> > the
> > >>> DTO. This gets tedious quickly. I wondered if there's not another
> way
> > >>> that people are doing this, because this seems entirely too painful.
> > >>>
> > >>> However, if* this is* what most people do, then perhaps a change
> could
> > be
> > >>> made to the modeler, that would all you to create automatically a set
> > of
> > >>> DTO objects with when you generate the model objects. I recognize
> that
> > >>> this would be a rather significant effort and I'm guessing that
> there's
> > >>> probably a better way, but I'm not aware of what it is.
> > >>>
> > >>> Any suggestions?
> > >>>
> > >>>
> > >>> Tony Giaccone
> > >>>
> > >
> >
>
