Re: [Wicket-user] Chicken-and-egg w/ Data Provider
So you need two queries in your data layer, one which returns a subset
of the query results for the particular page, and one which returns the
size of the potential result set (i.e. COUNT(*)).
There's no other way to implement this sensibly.
For Hibernate Criteria queries, this can look like this:
criteria.setProjection(Projections.rowCount()).uniqueResult();
I also have a HibernateIterator which will take a criteria and give you
a ScrollableResults, so if your database supports cursors properly then
you don't even need to load all the results for a single page at once
(not that this should generally be an issue).
I then have a class that implements IDataProvider and does the above.
Regards,
Al
V. Jenks wrote:
I prefer not to do it that way because it requires a potentially large list
of records to be pulled up initially whereas now, I'm only pulling the
records on the current page, making it much faster. I pass the x y right
through to the data access layer.
Johan Compagner wrote:
this only works if you have a seperate method:
private List getOrders()
{
if (orders == null)
{
orders = DAO.getOrders()
}
}
iterator()
{
return getOrders().sublist(x,y).iterator()
}
size()
{
return getOrders().size();
}
detach()
{
orders = null;
}
johan
On 5/29/07, V. Jenks [EMAIL PROTECTED] wrote:
I'm trying to use a provider class for a DataView so I can do
paging/sorting,
etc. It looks like this:
public class OrderProvider implements IDataProvider
{
private transient ListOrder orders;
public OrderProvider()
{
}
public Iterator iterator(int first, int count)
{
this.orders =
WicketHelper.ListOrdergetDetachedModelObject(
OrderProxy.getAll(first, first + count));
return this.orders.iterator();
}
public IModel model(Object model)
{
return WicketHelper.getDetachedModel(model);
}
public int size()
{
return this.orders.size();
}
}
I thought this would work but it looks like size() is called first, since
I
get a NPE:
Caused by: java.lang.NullPointerException
at com.myapp.provider.OrderProvider.size(OrderProvider.java:36)
It works if size() makes a call to the database to get a count of
records...but I'm trying to use a global field to prevent that data call.
Any suggestions?
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Re: [Wicket-user] Chicken-and-egg w/ Data Provider
this only works if you have a seperate method:
private List getOrders()
{
if (orders == null)
{
orders = DAO.getOrders()
}
}
iterator()
{
return getOrders().sublist(x,y).iterator()
}
size()
{
return getOrders().size();
}
detach()
{
orders = null;
}
johan
On 5/29/07, V. Jenks [EMAIL PROTECTED] wrote:
I'm trying to use a provider class for a DataView so I can do
paging/sorting,
etc. It looks like this:
public class OrderProvider implements IDataProvider
{
private transient ListOrder orders;
public OrderProvider()
{
}
public Iterator iterator(int first, int count)
{
this.orders =
WicketHelper.ListOrdergetDetachedModelObject(
OrderProxy.getAll(first, first + count));
return this.orders.iterator();
}
public IModel model(Object model)
{
return WicketHelper.getDetachedModel(model);
}
public int size()
{
return this.orders.size();
}
}
I thought this would work but it looks like size() is called first, since
I
get a NPE:
Caused by: java.lang.NullPointerException
at com.myapp.provider.OrderProvider.size(OrderProvider.java:36)
It works if size() makes a call to the database to get a count of
records...but I'm trying to use a global field to prevent that data call.
Any suggestions?
--
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Re: [Wicket-user] Chicken-and-egg w/ Data Provider
The size() method was one of my biggest stumbling blocks when I started using
DataProvders, but for slightly different reasons (i.e. just having a size
method makes it less maintainable, perform worse, less scalable and gives
less accurate results). But when I tried to work around the size method, I
found it was very deeply embedded in the inner workings of DataTable. I
also think DataTable is too nice of a component to not use. So I came up
with a solution that doesn't require the DataProvider to have a size()
method, but leaves it in DataTable. I've submitted this to JIRA
(https://issues.apache.org/jira/browse/WICKET-579), but since it requires
changing core classes, I wouldn't suggest anybody implement it before it is
an accepted patch. (but maybe some support from others will help it get
accepted).
Kurt
James McLaughlin-3 wrote:
The purpose of size() is to give the DataView an idea of how many
pages there will be, so this really won't work. You should fetch size
in a separate query as the number of orders total over all pages, and
cache that.
best,
jim
On 5/29/07, V. Jenks [EMAIL PROTECTED] wrote:
I'm trying to use a provider class for a DataView so I can do
paging/sorting,
etc. It looks like this:
public class OrderProvider implements IDataProvider
{
private transient ListOrder orders;
public OrderProvider()
{
}
public Iterator iterator(int first, int count)
{
this.orders =
WicketHelper.ListOrdergetDetachedModelObject(
OrderProxy.getAll(first, first + count));
return this.orders.iterator();
}
public IModel model(Object model)
{
return WicketHelper.getDetachedModel(model);
}
public int size()
{
return this.orders.size();
}
}
I thought this would work but it looks like size() is called first, since
I
get a NPE:
Caused by: java.lang.NullPointerException
at com.myapp.provider.OrderProvider.size(OrderProvider.java:36)
It works if size() makes a call to the database to get a count of
records...but I'm trying to use a global field to prevent that data call.
Any suggestions?
--
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Re: [Wicket-user] Chicken-and-egg w/ Data Provider
I prefer not to do it that way because it requires a potentially large list
of records to be pulled up initially whereas now, I'm only pulling the
records on the current page, making it much faster. I pass the x y right
through to the data access layer.
Johan Compagner wrote:
this only works if you have a seperate method:
private List getOrders()
{
if (orders == null)
{
orders = DAO.getOrders()
}
}
iterator()
{
return getOrders().sublist(x,y).iterator()
}
size()
{
return getOrders().size();
}
detach()
{
orders = null;
}
johan
On 5/29/07, V. Jenks [EMAIL PROTECTED] wrote:
I'm trying to use a provider class for a DataView so I can do
paging/sorting,
etc. It looks like this:
public class OrderProvider implements IDataProvider
{
private transient ListOrder orders;
public OrderProvider()
{
}
public Iterator iterator(int first, int count)
{
this.orders =
WicketHelper.ListOrdergetDetachedModelObject(
OrderProxy.getAll(first, first + count));
return this.orders.iterator();
}
public IModel model(Object model)
{
return WicketHelper.getDetachedModel(model);
}
public int size()
{
return this.orders.size();
}
}
I thought this would work but it looks like size() is called first, since
I
get a NPE:
Caused by: java.lang.NullPointerException
at com.myapp.provider.OrderProvider.size(OrderProvider.java:36)
It works if size() makes a call to the database to get a count of
records...but I'm trying to use a global field to prevent that data call.
Any suggestions?
--
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http://www.nabble.com/Chicken-and-egg-w--Data-Provider-tf3834369.html#a10855464
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Re: [Wicket-user] Chicken-and-egg w/ Data Provider
The purpose of size() is to give the DataView an idea of how many
pages there will be, so this really won't work. You should fetch size
in a separate query as the number of orders total over all pages, and
cache that.
best,
jim
On 5/29/07, V. Jenks [EMAIL PROTECTED] wrote:
I'm trying to use a provider class for a DataView so I can do paging/sorting,
etc. It looks like this:
public class OrderProvider implements IDataProvider
{
private transient ListOrder orders;
public OrderProvider()
{
}
public Iterator iterator(int first, int count)
{
this.orders =
WicketHelper.ListOrdergetDetachedModelObject(
OrderProxy.getAll(first, first + count));
return this.orders.iterator();
}
public IModel model(Object model)
{
return WicketHelper.getDetachedModel(model);
}
public int size()
{
return this.orders.size();
}
}
I thought this would work but it looks like size() is called first, since I
get a NPE:
Caused by: java.lang.NullPointerException
at com.myapp.provider.OrderProvider.size(OrderProvider.java:36)
It works if size() makes a call to the database to get a count of
records...but I'm trying to use a global field to prevent that data call.
Any suggestions?
--
View this message in context:
http://www.nabble.com/Chicken-and-egg-w--Data-Provider-tf3834369.html#a10855464
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Re: [Wicket-user] Chicken-and-egg w/ Data Provider
On Tue, 29 May 2007, James McLaughlin wrote: The purpose of size() is to give the DataView an idea of how many pages there will be, so this really won't work. You should fetch size in a separate query as the number of orders total over all pages, and cache that. I think that in DataGridView (or something such that DataTable uses) this is already implemented, so you could have a look at that. - Timo -- Timo Rantalaiho Reaktor Innovations OyURL: http://www.ri.fi/ - This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ ___ Wicket-user mailing list Wicket-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wicket-user
