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 List<Order> orders;
>>>
>>> public OrderProvider()
>>> {
>>> }
>>>
>>> public Iterator iterator(int first, int count)
>>> {
>>> this.orders =
>>> WicketHelper.<List<Order>>getDetachedModelObject(
>>> 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
>>> Sent from the Wicket - User mailing list archive at Nabble.com.
>>>
>>>
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>
--
Alastair Maw
Wicket-biased blog at http://herebebeasties.com
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