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Posted to users@myfaces.apache.org by Enrique Medina <e....@gmail.com> on 2005/06/18 20:16:54 UTC
DataScroller & Lazy loading collections
Hi,
Maybe this is not the most adequate forum to post this question, but I
know many of you are using MyFaces together with Spring & Hibernate,
so it would be great it you give me some comments.
The problem I have comes with Lazy collections in my objects. Assuming
you know how to use Hibernate & Spring, the problem comes when I try
to paginate my DataTable using the DataScroller, because the
OpenSessionInViewFilter pattern establishes the session Hibernate in
the initial query (the one that shows the first page of the
DataTable). So, when the following page is needed, as MyFaces executes
a new request, the session binded by the OpenSessionInViewFilter for
this new request, is not obviously the same as the session previously
established at the first request.
Finally, I always get a Lazy initialization exception from Hibernate,
as you surely have imagined...
So my question is very simple:
How do you manage objects with lazy collections being shown in
different request with respect to the OpenSessionInViewFilter pattern?
Thanks in advance. I'm looking forward to hearing your comments.
Enrique Medina.
Re: DataScroller & Lazy loading collections
Posted by Werner Punz <we...@gmx.at>.
Enrique Medina wrote:
> Hi Werner,
>
> As we've been discussing, I'm only interested in getting a reference
> to the object being processed by each row in the DataTable, so IMHO
> the perfect point to get it is in the getRowData method.
>
> Currently, I'm loading the entire collection at once. This is an
> interesting area of discussion about pagination. After some
> investigation and comments from other developers, I ended up by just
> retrieving an exact number of records, e.g. the first 1000, because it
> does makes not make so much sense to implement such a complicated
> DataModel, and it would be as simple as asking the users to refine
> their searching criteria. So I simply use the Criteria API with
> set
Ok thanks for the clarification, btw. thanks for pointing me towards
that spring interceptor class, this one might solve a huge problem for
me in the near future (I always shied away of adding shale,
because I did not want to introduce a framework which is under
fluctuation into my core codebase)
Re: DataScroller & Lazy loading collections
Posted by Enrique Medina <e....@gmail.com>.
Hi Werner,
As we've been discussing, I'm only interested in getting a reference
to the object being processed by each row in the DataTable, so IMHO
the perfect point to get it is in the getRowData method.
Currently, I'm loading the entire collection at once. This is an
interesting area of discussion about pagination. After some
investigation and comments from other developers, I ended up by just
retrieving an exact number of records, e.g. the first 1000, because it
does makes not make so much sense to implement such a complicated
DataModel, and it would be as simple as asking the users to refine
their searching criteria. So I simply use the Criteria API with
setMaxResults(int max) to limit the number of results.
2005/6/21, Werner Punz <we...@gmx.at>:
> Interesting approach, I would have implemented a full model to do it,
> like I recommended.
> But yours looks much more compact.
> I never thought of applying a delegate to an existing model.
>
> Just a minor question, do you have callbacks into the setRowIndex method
> as well, because I just wonder if you load the entire collection at once
> or the objects only by demand.
>
> The reason why I am asking this is, that you might bet a much better
> mem footprint if you apply the rowIndex callbacks as well and use an
> iterator, because to my knowledge only the page data is requested
> normally, not the entire collection, if you enable the datatable paging.
>
>
> Werner
>
>
> Enrique Medina wrote:
> > Hi again,
> >
> > I finally solved my problem ;-)
> >
> > As I told you, I have extended the ListDataModel class to provide it
> > with a callback mechanism to be able to reattach any object to the
> > current Hibernate session.
> >
> > Let me show you the code:
> >
> > // Provide the callback within the constructor.
> > public LazyListDataModel(List list, DataModelCallback dataModelCallback)
> > {
> > super(list);
> >
> > this.dataModelCallback = dataModelCallback;
> > }
> >
> > // Overwritten method to call the provided callback method.
> > public Object getRowData()
> > {
> > // Get the object...
> > Object object = super.getRowData();
> >
> > // ...and call the callback method before returning the object.
> > if (this.dataModelCallback != null)
> > {
> > this.dataModelCallback.execute(object);
> > }
> >
> > return object ;
> > }
> >
> > Then, the DataModelCallback is a simple interface:
> >
> > public interface DataModelCallback
> > {
> > public abstract void execute(Object object);
> > }
> >
> > And finally, I simply use this special lazy implementation of the
> > DataModel in my JSF bean:
> >
> > this.workingDataModel = new LazyListDataModel(this.searchData(), new
> > DataModelCallback()
> > {
> > public void execute()
> > {
> > // Call Hibernate's lock stuff...
> > }
> > }
> >
>
>
Re: DataScroller & Lazy loading collections
Posted by Werner Punz <we...@gmx.at>.
Interesting approach, I would have implemented a full model to do it,
like I recommended.
But yours looks much more compact.
I never thought of applying a delegate to an existing model.
Just a minor question, do you have callbacks into the setRowIndex method
as well, because I just wonder if you load the entire collection at once
or the objects only by demand.
The reason why I am asking this is, that you might bet a much better
mem footprint if you apply the rowIndex callbacks as well and use an
iterator, because to my knowledge only the page data is requested
normally, not the entire collection, if you enable the datatable paging.
Werner
Enrique Medina wrote:
> Hi again,
>
> I finally solved my problem ;-)
>
> As I told you, I have extended the ListDataModel class to provide it
> with a callback mechanism to be able to reattach any object to the
> current Hibernate session.
>
> Let me show you the code:
>
> // Provide the callback within the constructor.
> public LazyListDataModel(List list, DataModelCallback dataModelCallback)
> {
> super(list);
>
> this.dataModelCallback = dataModelCallback;
> }
>
> // Overwritten method to call the provided callback method.
> public Object getRowData()
> {
> // Get the object...
> Object object = super.getRowData();
>
> // ...and call the callback method before returning the object.
> if (this.dataModelCallback != null)
> {
> this.dataModelCallback.execute(object);
> }
>
> return object ;
> }
>
> Then, the DataModelCallback is a simple interface:
>
> public interface DataModelCallback
> {
> public abstract void execute(Object object);
> }
>
> And finally, I simply use this special lazy implementation of the
> DataModel in my JSF bean:
>
> this.workingDataModel = new LazyListDataModel(this.searchData(), new
> DataModelCallback()
> {
> public void execute()
> {
> // Call Hibernate's lock stuff...
> }
> }
>
Re: DataScroller & Lazy loading collections
Posted by Enrique Medina <e....@gmail.com>.
Hi again,
I finally solved my problem ;-)
As I told you, I have extended the ListDataModel class to provide it
with a callback mechanism to be able to reattach any object to the
current Hibernate session.
Let me show you the code:
// Provide the callback within the constructor.
public LazyListDataModel(List list, DataModelCallback dataModelCallback)
{
super(list);
this.dataModelCallback = dataModelCallback;
}
// Overwritten method to call the provided callback method.
public Object getRowData()
{
// Get the object...
Object object = super.getRowData();
// ...and call the callback method before returning the object.
if (this.dataModelCallback != null)
{
this.dataModelCallback.execute(object);
}
return object ;
}
Then, the DataModelCallback is a simple interface:
public interface DataModelCallback
{
public abstract void execute(Object object);
}
And finally, I simply use this special lazy implementation of the
DataModel in my JSF bean:
this.workingDataModel = new LazyListDataModel(this.searchData(), new
DataModelCallback()
{
public void execute()
{
// Call Hibernate's lock stuff...
}
}
It works like a charm :-)
2005/6/20, Werner Punz <we...@gmx.at>:
> Enrique Medina wrote:
> > Hi,
> >
> > Maybe this is not the most adequate forum to post this question, but I
> > know many of you are using MyFaces together with Spring & Hibernate,
> > so it would be great it you give me some comments.
> >
> > The problem I have comes with Lazy collections in my objects. Assuming
> > you know how to use Hibernate & Spring, the problem comes when I try
> > to paginate my DataTable using the DataScroller, because the
> > OpenSessionInViewFilter pattern establishes the session Hibernate in
> > the initial query (the one that shows the first page of the
> > DataTable). So, when the following page is needed, as MyFaces executes
> > a new request, the session binded by the OpenSessionInViewFilter for
> > this new request, is not obviously the same as the session previously
> > established at the first request.
> >
> > Finally, I always get a Lazy initialization exception from Hibernate,
> > as you surely have imagined...
> >
> Ok sorry for the wild guessing in the last mails, I just read up
> the spring docs, and I now have a clearer picture of things. I think I
> can point you towards a definitive solution now.
>
> The lazy loading and the old objects BINDING approach you follow is
> rather unnecessary if you use a datamodel instead of feeding old objects
> into the session (probably via a collection you have stored somewhere in
> the session scope).
>
> > So my question is very simple:
> >
> > How do you manage objects with lazy collections being shown in
> > different request with respect to the OpenSessionInViewFilter pattern?
> >
> > Thanks in advance. I'm looking forward to hearing your comments.
> >
> > Enrique Medina.
> >
>
> O think I know where your problems is, you try to recycle the old
> objects in a new session which is opened automatically.
> The objects are probably stored in a session scoped collection
> and then fed back into the model after the request (which is caused
> by the paging), theoretically you could use bind to lock them to the new
> session, but that is problematic and not really necessary.
>
> The best way to solve your problem if you dont want to go the shale
> route (which basically does the same as the Spring class in a safer way)
> is, just to implement a pure datamodel,
> you get the session from spring anyway, and feed the data from the
> methods you have to implement from the model, just as you guessed.
>
> The call apprach probably will go like that
> Constructor of the model... request the session from spring, which is
> already opened
> The next callbacks are for delivering the number of rows etc...
> then load the object row by row as the outer system requests it from the
> model and you are set...
>
> For performance increase you probably can
> set an iterator on the give me the number of rows methods
> and then recycle that one for each subsequent, give me the next row
> request. That way it should work.
>
> Sorry for the guessing from my side in the last mails. I overlooked the
> Spring part.
>
> Either way, you probably will have to implement a specialized datamodel.
>
>
Re: DataScroller & Lazy loading collections
Posted by Werner Punz <we...@gmx.at>.
Enrique Medina wrote:
> Hi,
>
> Maybe this is not the most adequate forum to post this question, but I
> know many of you are using MyFaces together with Spring & Hibernate,
> so it would be great it you give me some comments.
>
> The problem I have comes with Lazy collections in my objects. Assuming
> you know how to use Hibernate & Spring, the problem comes when I try
> to paginate my DataTable using the DataScroller, because the
> OpenSessionInViewFilter pattern establishes the session Hibernate in
> the initial query (the one that shows the first page of the
> DataTable). So, when the following page is needed, as MyFaces executes
> a new request, the session binded by the OpenSessionInViewFilter for
> this new request, is not obviously the same as the session previously
> established at the first request.
>
> Finally, I always get a Lazy initialization exception from Hibernate,
> as you surely have imagined...
>
Ok sorry for the wild guessing in the last mails, I just read up
the spring docs, and I now have a clearer picture of things. I think I
can point you towards a definitive solution now.
The lazy loading and the old objects BINDING approach you follow is
rather unnecessary if you use a datamodel instead of feeding old objects
into the session (probably via a collection you have stored somewhere in
the session scope).
> So my question is very simple:
>
> How do you manage objects with lazy collections being shown in
> different request with respect to the OpenSessionInViewFilter pattern?
>
> Thanks in advance. I'm looking forward to hearing your comments.
>
> Enrique Medina.
>
O think I know where your problems is, you try to recycle the old
objects in a new session which is opened automatically.
The objects are probably stored in a session scoped collection
and then fed back into the model after the request (which is caused
by the paging), theoretically you could use bind to lock them to the new
session, but that is problematic and not really necessary.
The best way to solve your problem if you dont want to go the shale
route (which basically does the same as the Spring class in a safer way)
is, just to implement a pure datamodel,
you get the session from spring anyway, and feed the data from the
methods you have to implement from the model, just as you guessed.
The call apprach probably will go like that
Constructor of the model... request the session from spring, which is
already opened
The next callbacks are for delivering the number of rows etc...
then load the object row by row as the outer system requests it from the
model and you are set...
For performance increase you probably can
set an iterator on the give me the number of rows methods
and then recycle that one for each subsequent, give me the next row
request. That way it should work.
Sorry for the guessing from my side in the last mails. I overlooked the
Spring part.
Either way, you probably will have to implement a specialized datamodel.
Re: DataScroller & Lazy loading collections
Posted by Enrique Medina <e....@gmail.com>.
Hi Jonathan,
Yes, I know that issue, but it does not fit into my scenario because:
a) I really want to do lazy loading
b) I'm currently using the Criteria API, as I have a dynamic set of
criterion in my form, where the user can enter either all the criteria
or just something or even none, so the SQL must be dynamically
created. The Criteria by Example is perfect for this, while using HQL
would lead to annoying if...then... clauses
So in resume, I could have made the lazy collections to be prefecthed
also using the Criteria API, but that's not the behaviour I was
requiring ;-)
2005/6/20, Jonathan Eric Miller <je...@uchicago.edu>:
> I don't know if you already know this and there's a reason why you aren't
> doing it this way or not, but, in HQL, you can use "fetch" to tell it to do
> an immediate load of collections even if the mapping files specify them as
> lazy.
>
> Jon
>
> ----- Original Message -----
> From: "Enrique Medina" <e....@gmail.com>
> To: "MyFaces Discussion" <us...@myfaces.apache.org>
> Sent: Saturday, June 18, 2005 1:16 PM
> Subject: DataScroller & Lazy loading collections
>
> > Hi,
> >
> > Maybe this is not the most adequate forum to post this question, but I
> > know many of you are using MyFaces together with Spring & Hibernate,
> > so it would be great it you give me some comments.
> >
> > The problem I have comes with Lazy collections in my objects. Assuming
> > you know how to use Hibernate & Spring, the problem comes when I try
> > to paginate my DataTable using the DataScroller, because the
> > OpenSessionInViewFilter pattern establishes the session Hibernate in
> > the initial query (the one that shows the first page of the
> > DataTable). So, when the following page is needed, as MyFaces executes
> > a new request, the session binded by the OpenSessionInViewFilter for
> > this new request, is not obviously the same as the session previously
> > established at the first request.
> >
> > Finally, I always get a Lazy initialization exception from Hibernate,
> > as you surely have imagined...
> >
> > So my question is very simple:
> >
> > How do you manage objects with lazy collections being shown in
> > different request with respect to the OpenSessionInViewFilter pattern?
> >
> > Thanks in advance. I'm looking forward to hearing your comments.
> >
> > Enrique Medina.
> >
>
>
Re: DataScroller & Lazy loading collections
Posted by Jonathan Eric Miller <je...@uchicago.edu>.
I don't know if you already know this and there's a reason why you aren't
doing it this way or not, but, in HQL, you can use "fetch" to tell it to do
an immediate load of collections even if the mapping files specify them as
lazy.
Jon
----- Original Message -----
From: "Enrique Medina" <e....@gmail.com>
To: "MyFaces Discussion" <us...@myfaces.apache.org>
Sent: Saturday, June 18, 2005 1:16 PM
Subject: DataScroller & Lazy loading collections
> Hi,
>
> Maybe this is not the most adequate forum to post this question, but I
> know many of you are using MyFaces together with Spring & Hibernate,
> so it would be great it you give me some comments.
>
> The problem I have comes with Lazy collections in my objects. Assuming
> you know how to use Hibernate & Spring, the problem comes when I try
> to paginate my DataTable using the DataScroller, because the
> OpenSessionInViewFilter pattern establishes the session Hibernate in
> the initial query (the one that shows the first page of the
> DataTable). So, when the following page is needed, as MyFaces executes
> a new request, the session binded by the OpenSessionInViewFilter for
> this new request, is not obviously the same as the session previously
> established at the first request.
>
> Finally, I always get a Lazy initialization exception from Hibernate,
> as you surely have imagined...
>
> So my question is very simple:
>
> How do you manage objects with lazy collections being shown in
> different request with respect to the OpenSessionInViewFilter pattern?
>
> Thanks in advance. I'm looking forward to hearing your comments.
>
> Enrique Medina.
>
Re: DataScroller & Lazy loading collections
Posted by Werner Punz <we...@gmx.at>.
Enrique Medina wrote:
> Hi Werner,
>
> What I would try to achieve with the callback mechanism would be
> simply to get the reference to the current object, and reattach it to
> the current session. Please take into account that I'm currently using
> the OpenSessionInViewFilter pattern from Spring, so the session would
> be automatically opened and closed in a transparent way.
>
Ok I am not familiar with that one, I have to look that up
(I have to admit I use Spring also, but for other stuff)
if this one works well then you are set, but it seems rather that it
does not really do the stuff you want to achieve.
> So the only hit in performance would be the call to
> Hibernate.lock(object, LockMode.NONE) for each object in each row in
> the DataModel. If there are many of them, maybe it's worth the effort
> instead of having to preload everything into memory, without lazy
> loading it.
>
well as I said I have to read that Spring pattern up, but the datamodel
is pure read only, so no lock is required.
I will try to explain the flow from the datatable control to the
datamodel...
First the datamodel is initialized, then a request is started for the
number of rows, then row by row the model is asked to deliver the data
and the row counter is increased.
Once the rendering is finished the rows basically are not requested
anymore but nothing is sent to the datamodel to free the resources
(shale fixes that).
Now to your lazy loading, for some strange kind of reason you seem to
loose the session along the way.
Since you do pagination, and that is the huge leak I see in my
understanding of things, since I do not know exactly what the
OpenSessionInViewFilter does, is that the session probably is not
reopened or closed to early. (It is probably closed after the first
loading and never triggered again or closed to early)
Thus you run into the lazy loading problem.
There seems to be a problem between the way the datamodel is handled
internally and the OpensessionInViewFilter is triggered.
My guess is that the pagination basically has to store some data in the
session or server and thus, the pagination basically Interferes with the
OpenSessionInViewFilter.
> What do you think? I've been looking at ListDataModel implementation
> of the DataModel interface, and it could be easily extended with a
> callback mechanism every time the getRowData is invoked...
>
exactly that is the way to do it, as I said, the shale datamodel
approach might be the best to solve your problem, since you have full
control over the session/transaction scope that way.
(I have something with a prefetch caching window sort of working-without
shale, but I am not happy with that, because that one also has the lazy
loading problem, you describe)
Re: DataScroller & Lazy loading collections
Posted by Enrique Medina <e....@gmail.com>.
Hi Werner,
What I would try to achieve with the callback mechanism would be
simply to get the reference to the current object, and reattach it to
the current session. Please take into account that I'm currently using
the OpenSessionInViewFilter pattern from Spring, so the session would
be automatically opened and closed in a transparent way.
So the only hit in performance would be the call to
Hibernate.lock(object, LockMode.NONE) for each object in each row in
the DataModel. If there are many of them, maybe it's worth the effort
instead of having to preload everything into memory, without lazy
loading it.
What do you think? I've been looking at ListDataModel implementation
of the DataModel interface, and it could be easily extended with a
callback mechanism every time the getRowData is invoked...
2005/6/20, Werner Punz <we...@gmx.at>:
> Enrique Medina wrote:
> > Umm, I see.
> >
> > But shouldn't it be interesting for this specific problem to just have
> > some kind of callback mechanism in the DataModel, so you could 'do
> > something' everytime a row is rendered?
> >
> Actually the current datamodel interface has such a method, getRowData
> is called every time a row is rendered and then the row counter is
> increased.
> Sure you theoretically could open a session every time a row is
> rendered and then drop it, that might work for small prototypes, but
> you basically push the performance down the garbage (sorry for the pun)
> if you do that, because in the best case sessions get recycled
> and transactions are opened and closed constantly, in the worst case
> the sessions also are opened and dropped every time you
> have a row fetched.
>
> I think you get the picture on where the basic flaw in the current
> datamodel mechanism is. The current datamodel mechanism is basically
> only suited to situations where you can keep the connections open (and
> also the transactions if possible), because of the missing callback
> points which notify the model on when it can aquire resources and drop
> them again.
> You might get around that problem to a certain extent by using JTA, but
> I am not too familiar with it.
> (The studio creator uses it to bypass the problem)
>
>
> > I mean, you could get a reference to the current object in order to
> > reattach it to the new session...
> >
> Well you cannot keep the sessions open forever, I am not sure on what
> you want to do, but if you have more than a handful of users, you should
> drop the session after the entire page is rendered, after all you dont
> know what the user is going to do.
> Once you write the object back you have to reattach the object anyway to
> the next opened session, which is responsible for the write back.
>
>
> > What do you think? Maybe it's as simpler as reimplementing the actual
> > DataModel with callback mechanisms...
> >
> Well to my knowledge you cannot avoid having to implement the entire
> datamodel mechanism and then you run into the scope problems, which are
> also connected to your lazy loading problems.
>
> So you have several options left to get rid of your lazy loading problem.
>
> Use shale and write your own shaled datamodel with clear callbacks which
> notify the datamodel on when to aquire and drop the session and be done
> with it.
>
> Use JTA and hope that it works as you need it (which I cannot really
> assure you since I dont know jta really).
>
> Preload everything you want to display either by tweaking the hibernate
> configuration files or doing a manual load of the parts you want to
> display within the session scope (which is what I did because I did not
> know the shale solution at that time).
>
> Hope, that somebody solves the problem for you in a convenient way,
> before the next deadline. Which is very unlikely to happen.
>
> My personal opinion is, that shale might be the best approach for your
> problem in the long term. The manual preloading, messing around with the
> config files, might be to messy and too error prone in the long run.
>
>
Re: DataScroller & Lazy loading collections
Posted by Werner Punz <we...@gmx.at>.
Enrique Medina wrote:
> Umm, I see.
>
> But shouldn't it be interesting for this specific problem to just have
> some kind of callback mechanism in the DataModel, so you could 'do
> something' everytime a row is rendered?
>
Actually the current datamodel interface has such a method, getRowData
is called every time a row is rendered and then the row counter is
increased.
Sure you theoretically could open a session every time a row is
rendered and then drop it, that might work for small prototypes, but
you basically push the performance down the garbage (sorry for the pun)
if you do that, because in the best case sessions get recycled
and transactions are opened and closed constantly, in the worst case
the sessions also are opened and dropped every time you
have a row fetched.
I think you get the picture on where the basic flaw in the current
datamodel mechanism is. The current datamodel mechanism is basically
only suited to situations where you can keep the connections open (and
also the transactions if possible), because of the missing callback
points which notify the model on when it can aquire resources and drop
them again.
You might get around that problem to a certain extent by using JTA, but
I am not too familiar with it.
(The studio creator uses it to bypass the problem)
> I mean, you could get a reference to the current object in order to
> reattach it to the new session...
>
Well you cannot keep the sessions open forever, I am not sure on what
you want to do, but if you have more than a handful of users, you should
drop the session after the entire page is rendered, after all you dont
know what the user is going to do.
Once you write the object back you have to reattach the object anyway to
the next opened session, which is responsible for the write back.
> What do you think? Maybe it's as simpler as reimplementing the actual
> DataModel with callback mechanisms...
>
Well to my knowledge you cannot avoid having to implement the entire
datamodel mechanism and then you run into the scope problems, which are
also connected to your lazy loading problems.
So you have several options left to get rid of your lazy loading problem.
Use shale and write your own shaled datamodel with clear callbacks which
notify the datamodel on when to aquire and drop the session and be done
with it.
Use JTA and hope that it works as you need it (which I cannot really
assure you since I dont know jta really).
Preload everything you want to display either by tweaking the hibernate
configuration files or doing a manual load of the parts you want to
display within the session scope (which is what I did because I did not
know the shale solution at that time).
Hope, that somebody solves the problem for you in a convenient way,
before the next deadline. Which is very unlikely to happen.
My personal opinion is, that shale might be the best approach for your
problem in the long term. The manual preloading, messing around with the
config files, might be to messy and too error prone in the long run.
Re: DataScroller & Lazy loading collections
Posted by Enrique Medina <e....@gmail.com>.
Umm, I see.
But shouldn't it be interesting for this specific problem to just have
some kind of callback mechanism in the DataModel, so you could 'do
something' everytime a row is rendered?
I mean, you could get a reference to the current object in order to
reattach it to the new session...
What do you think? Maybe it's as simpler as reimplementing the actual
DataModel with callback mechanisms...
2005/6/20, Werner Punz <we...@gmx.at>:
> Enrique Medina wrote:
> > Hi Werner,
> >
> > I see. Regarding to your comments about Shale, do you mean that Shale
> > will allow me to have a reference to every object that is prsented in
> > the DataModel, so for example I will be able to reattach it to the new
> > Hibernate session using Hibernate.lock(object, LockMode.NONE)?
> >
> No... from what I could gather from Clanahans comments you will
> finally get clear demarkation boundaries on when you can aquire
> resources before rendering and when you can drop it after the rendering
> is done.
> Shale finally has a mechanism which you can bend towards following states.
>
> 1) I am before rendering aquire the resources you need
> 2) Rendering is done release the resources.
>
> That means you finally know when the rendering starts and can aquire the
> session, and then finally you also know when the rendering is done and
> you can drop the session.
> In your case this helps for the data table that you can open the session
> at the beginning of the rendering stage, you can use lazy loading to
> load the data just needed for the data table, and once the rendering is
> done you can drop the session.
>
> The current state of affairs is, you have to preload the data and serve
> it row by row (object by object) and thus you cannot keep the session,
> open during rendering, or you have to keep the session open until a
> stage you cannot control anymore. Therefore you automatically if you
> follow the first approach, you run into lazy loading problems, you have
> to resolve manually.
>
> Here is the original comment of Clanahan on which mechanism you can use
> to resolve the whole issue:
>
> -----
>
> Solving these sorts of problems is exactly what the Shale framework
> (part of the Struts project) is designed to address. Current starting
> point for info is on the wiki (i'm working up the docs for the
> website).
>
> http://wiki.apache.org/struts/StrutsShale
>
> You'll be interested particularly in the ViewController interface, and
> the fact that it gives you event callbacks at the beginning and end of
> a view (init and destroy) and well as other events dependent upon
> whether you are processing a form submit or not (preprocess and
> prerender). Shale presumes that JSF exists, and leverages its front
> controller framework rather than treating JSF just as a mechanism for
> constructing the view.
>
>
Re: DataScroller & Lazy loading collections
Posted by Werner Punz <we...@gmx.at>.
Enrique Medina wrote:
> Hi Werner,
>
> I see. Regarding to your comments about Shale, do you mean that Shale
> will allow me to have a reference to every object that is prsented in
> the DataModel, so for example I will be able to reattach it to the new
> Hibernate session using Hibernate.lock(object, LockMode.NONE)?
>
No... from what I could gather from Clanahans comments you will
finally get clear demarkation boundaries on when you can aquire
resources before rendering and when you can drop it after the rendering
is done.
Shale finally has a mechanism which you can bend towards following states.
1) I am before rendering aquire the resources you need
2) Rendering is done release the resources.
That means you finally know when the rendering starts and can aquire the
session, and then finally you also know when the rendering is done and
you can drop the session.
In your case this helps for the data table that you can open the session
at the beginning of the rendering stage, you can use lazy loading to
load the data just needed for the data table, and once the rendering is
done you can drop the session.
The current state of affairs is, you have to preload the data and serve
it row by row (object by object) and thus you cannot keep the session,
open during rendering, or you have to keep the session open until a
stage you cannot control anymore. Therefore you automatically if you
follow the first approach, you run into lazy loading problems, you have
to resolve manually.
Here is the original comment of Clanahan on which mechanism you can use
to resolve the whole issue:
-----
Solving these sorts of problems is exactly what the Shale framework
(part of the Struts project) is designed to address. Current starting
point for info is on the wiki (i'm working up the docs for the
website).
http://wiki.apache.org/struts/StrutsShale
You'll be interested particularly in the ViewController interface, and
the fact that it gives you event callbacks at the beginning and end of
a view (init and destroy) and well as other events dependent upon
whether you are processing a form submit or not (preprocess and
prerender). Shale presumes that JSF exists, and leverages its front
controller framework rather than treating JSF just as a mechanism for
constructing the view.
Re: DataScroller & Lazy loading collections
Posted by Enrique Medina <e....@gmail.com>.
Hi Werner,
I see. Regarding to your comments about Shale, do you mean that Shale
will allow me to have a reference to every object that is prsented in
the DataModel, so for example I will be able to reattach it to the new
Hibernate session using Hibernate.lock(object, LockMode.NONE)?
Thanks for your comments.
2005/6/20, Werner Punz <we...@gmx.at>:
> Enrique Medina wrote:
> > Hi,
> >
> > Maybe this is not the most adequate forum to post this question, but I
> > know many of you are using MyFaces together with Spring & Hibernate,
> > so it would be great it you give me some comments.
> >
> > The problem I have comes with Lazy collections in my objects. Assuming
> > you know how to use Hibernate & Spring, the problem comes when I try
> > to paginate my DataTable using the DataScroller, because the
> > OpenSessionInViewFilter pattern establishes the session Hibernate in
> > the initial query (the one that shows the first page of the
> > DataTable). So, when the following page is needed, as MyFaces executes
> > a new request, the session binded by the OpenSessionInViewFilter for
> > this new request, is not obviously the same as the session previously
> > established at the first request.
> >
> > Finally, I always get a Lazy initialization exception from Hibernate,
> > as you surely have imagined...
> >
> > So my question is very simple:
> >
> > How do you manage objects with lazy collections being shown in
> > different request with respect to the OpenSessionInViewFilter pattern?
> >
> Simple answer, to a relatively deep question. You cannot. To be more
> precise, there is a huge flaw in the access pattern of the Datamodel,
> which is somewhat fixed in shale (Clanahan, the core maintainer of Shale
> pointed me towards it), and that is the way you can get access
> boundaries in the Datamodel, which is somewhat non existent.
>
> But back to your problem which has more to do with Hibernate than with
> the half broken Datamodel.
> The easiest way to deal with your problem is relatively simple, avoid
> the lazy loading for the parts you want to display in the data table
> and only use it for the parts you dont want to display, to avoid
> excessive data loading.
> You can do that either by tinkering with the Hibernate config params, or
> by accessing the lazily loaded parts during session time once.
> Depending on your data structures one approach or the other might
> be more efficient.
>
>
Re: DataScroller & Lazy loading collections
Posted by Werner Punz <we...@gmx.at>.
Enrique Medina wrote:
> Hi,
>
> Maybe this is not the most adequate forum to post this question, but I
> know many of you are using MyFaces together with Spring & Hibernate,
> so it would be great it you give me some comments.
>
> The problem I have comes with Lazy collections in my objects. Assuming
> you know how to use Hibernate & Spring, the problem comes when I try
> to paginate my DataTable using the DataScroller, because the
> OpenSessionInViewFilter pattern establishes the session Hibernate in
> the initial query (the one that shows the first page of the
> DataTable). So, when the following page is needed, as MyFaces executes
> a new request, the session binded by the OpenSessionInViewFilter for
> this new request, is not obviously the same as the session previously
> established at the first request.
>
> Finally, I always get a Lazy initialization exception from Hibernate,
> as you surely have imagined...
>
> So my question is very simple:
>
> How do you manage objects with lazy collections being shown in
> different request with respect to the OpenSessionInViewFilter pattern?
>
Simple answer, to a relatively deep question. You cannot. To be more
precise, there is a huge flaw in the access pattern of the Datamodel,
which is somewhat fixed in shale (Clanahan, the core maintainer of Shale
pointed me towards it), and that is the way you can get access
boundaries in the Datamodel, which is somewhat non existent.
But back to your problem which has more to do with Hibernate than with
the half broken Datamodel.
The easiest way to deal with your problem is relatively simple, avoid
the lazy loading for the parts you want to display in the data table
and only use it for the parts you dont want to display, to avoid
excessive data loading.
You can do that either by tinkering with the Hibernate config params, or
by accessing the lazily loaded parts during session time once.
Depending on your data structures one approach or the other might
be more efficient.