Date: Tue, 18 Dec 2012 14:00:05 -0800
Gordon,
As long as an industry-level specification is concerned, "time
constraints" should never be a valid argument for introducing an
alternative that is difficult to justify later. If time is a constraint,
then it is better to hold back the feature for later releases.
The users need for a subgraph to another tier is adequately addressed
within detach-modify-merge cycle of JPA programming model, which is a
significant and useful departure from remotable EJB programming model of
earlier days. From that viewpoint, introduction of a copy() function is a
step backwards and, as mentioned in this thread, may promote a "dangerous"
programming model.
Regards --
Pinaki Poddar
Chair, Apache OpenJPA Project http://openjpa.apache.org/
JPA Expert Group Member
Application & Integration Middleware
From: Gordon Yorke <gordon.yorke_at_oracle.com>
To: jsr338-experts_at_jpa-spec.java.net
Date: 12/18/2012 01:22 PM
Subject: [jsr338-experts] Re: Proposal for EntityGraphs, fetch plans,
etc...
Hello Pinaki and others,
- detach(EntityGraph) is functionality we should introduce but the
semantics are more complicated than copy() and should be deferred because
of time constraints.
- the need derives from user requests. Users wish to create copies of a
graph of entities for many different reasons and currently they must
implement this functionality themselves.
- I believe we are discussing copy() separately from the discussions on
EntityGraphs and copy() exists as its own functionality but copy() is
enabled through EntityGraphs so the features are related and hence
introduced at the same time.
--Gordon
On 18/12/2012 2:15 PM, Pinaki Poddar wrote:
> I find the programming model quite error prone and dangerous.
+1
A separate copy() function does seem to add redundant complexity. As
such, creating copies often is the beginning of all sorts of
anti-patterns. If the need for a copy() is strongly felt, then
a) detach() with an option to leave the objects in the persistence
context can be considered to achieve similar functionality.
b) the need for a separate copy() should be articulated more clearly
c) in any case, the proposal for a copy() should be tabled separately
from EntityGraph specification.
Regards --
Pinaki Poddar
Chair, Apache OpenJPA Project http://openjpa.apache.org/
JPA Expert Group Member
Application & Integration Middleware
Inactive hide details for Emmanuel Bernard ---12/17/2012
09:12:47 AM---OK I get it now. To be honest I am quite
uncomfortable wEmmanuel Bernard ---12/17/2012 09:12:47 AM---OK I get
it now. To be honest I am quite uncomfortable with such a feature.
Does everyone
From: Emmanuel Bernard <ebernard_at_redhat.com>
To: jsr338-experts_at_jpa-spec.java.net
Date: 12/17/2012 09:12 AM
Subject: [jsr338-experts] Re: Proposal for EntityGraphs, fetch plans,
etc...
OK I get it now.
To be honest I am quite uncomfortable with such a feature. Does
everyone
really think that this feature is a must have?
I imagine that the use case you have in mind is to pass this copied
object graph to another serialization or traversal framework that
would
otherwise traverse the JPA guards like there is no tomorrow.
Our experience with Bean Validation has shown that handling guards is
extremely easy and that the necessary contract to make a traversal /
serialization framework aware of these is quite simple
https://github.com/beanvalidation/beanvalidation-api/blob/master/src/main/java/javax/validation/TraversableResolver.java
The solution proposed here (the copy) forces to copy an object graph
which leads to memory duplication just to get the data serialized in
another form. Plus the user *must* use the same graph definition for
both `copy` and `merge` or else data loss are going to happen. I find
the programming model quite error prone and dangerous.
Emmanuel
On Mon 2012-12-17 9:40, Gordon Yorke wrote:
> Hello Emmanuel,
> The goal of a copy graph is to produce a simple subgraph copy of
> the entity graph for environments where enhancement/proxies may not
> be available or where these "guards" can not be retained when then
> graph is serialized. The developer has a template in the form of
> the entity graph which provides the details of which attributes
have
> legitimate values and which ones should be ignored and this
template
> is highly recommended for the merge. There is no requirement for
> "guards" embedded within the copies. In client/server environments
> where "guards" would be available there is no need for copy() at
all
> as the same functionality is achieved serializing entities loaded
> with a fetch graph.
>
> --Gordon
> On 17/12/2012 5:25 AM, Emmanuel Bernard wrote:
> >>>## Use cases
> >>>
> >>>I would really like to get use cases associated to each of the
new
> >>>features proposed here.
> >>>
> >>>In particular:
> >>>- it's unclear to me why you really need loadgraph and
fetchgraph.
> >>>- why is merge( fetchgraph ) required when you can achieve the
same with
> >>> - find( fetchgraph )
> >>> - detach / serialize or whatever
> >>> - merge() regular method
> >>merge(EntityGraph) applies when the user is using copy
(EntityGraph)
> >>to detach an entity tree for serialization. If an attribute is
not
> >>present in the copy then it must not be merged. So, your example
> >>becomes:
> >> - find (EntityGraph eg1)
> >> - copy(EntityGraph eg1)
> >> - serialize out/in
> >> - merge(EntityGraph eg1)
> >Sure but the graph returned by copy does contain guards on
uninitialized
> >properties and associations right? Ie when a non copied property /
> >association is traversed, some exception is raised.
> >
> >If that's not the case then what are you returning? null or the
> >primitive default values? I would be strongly against that.
> >
> >So assuming the engine has those guards on uninitialized
properties and
> >associations, then the merge with an EntityGraph is not necessary
as
> >this information can be discovered (like we do for a regular
merge).
> >
> >Emmanuel
>
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