Squeeze adapters just make life simpler when dealing with direct links,
hidden form fields storing
an object necessary for the form, etc.
Consider, for example, the following:
<a href="#" jwcid=..irectLink" parameter="ognl:someDataObject">some
link</a>,
then w/out the squeeze adapter, you get the nasty serialized string
storing the object, like:
sp=zajwrk230jakzkeljk24j0jakljzlkjlkjlajk3wj0jzkjj2j1kjajajzkqweeraoiwr2412478997lksl2klaalkjoi4u389ull
Or whatever. :) The url is ugly, but when you get your Object[] array
in your listener, you have a nicely
inflated object. Or... /mostly/ nicely. The issue here is that you
wind up with a data object which isn't
connected to any data context. So... ugly url /and/ problematic.
To fix that, you could do (it's ugly all in ognl, but.... :)
<a href="#" jwcid=..irectLink"
parameter="ognl..rg.objectstyle.cayenne.DataObjectUtils@intPKForObject(someDataObject">some
link</a>
Which gives you a "nice" url parameter like:
sp=300
Of course, then in your corresponding listener code, you're going to
have to reverse that process... grab your object from your data context,
based on the pk. So, clean url, no disconnected dataobject problems,
but it's code that you essentially have to duplicate
over and over again.
Using the custom squeeze adapter, you would still do
parameter="ognl:someDataObject".
But then the generated url parameter would look something like:
sp=Pnt/DataObject/300
Still reasonably clean*, plus, you don't have to deal with the pk
yourself, plus when you get your array of objects in your listener,
you have a nicely "inflated" data object, /and/ it's connected to the
data context**, to boot. :) You grab your object and go.
It's certainly possible to /not/ use a squeeze adapter... tassel was
written without one. But having now written it,
I'd never go back to not using it. It's just one of those things which
makes life that much nicer. :)
Robert
*caveat: if object.getObjEntity() returns null (which is the case if
you used a newly created,
unregistered data object, the object is squeezed
according to the standard
tapestry mechanism, so you still get something of an
ugly url.
**caveat: if the object was not registered with a data context when it
was "squeezed", it won't be associated
with a data context when unsqueezed. Eg: parameter="new
org.me.SomeObject()"; said object
wouldn't be associated with a datacontext on
unsqueezing... and you wouldn't expect it to.
Eric Schneider wrote:
> Hi Robert,
>
> I probably haven't paid enough attention to the DataSqueezer posts on
> the Cayenne/Tapestry mailing lists. I was under the assumption you
> needed to implement a custom squeezer if you wanted bind a DataObject
> as a DirectLink parameter. Are there other instances where the
> standard Tapestry squeezing implementation with DataObjects jack me up?
>
> I just haven't come across a problem (with a handful of apps), but
> maybe I'm missing something?
>
> Thanks,
> Eric
>
> On Oct 25, 2005, at 10:59 AM, Robert Zeigler wrote:
>
>> Sorry, I must've missed your e-mail on the tapestry list.
>> Using the squeeze adapter is a matter of implementing the
>> two interfaces it requires. One is ObjectIdStorageProvider.
>> If you never use objects which are in state "NEW" in your pages,
>> then this interface is unimportant and you can have a "dummy"
>> implementation. Otherwise, what this interface is for is to
>> store (in memory) the (temporary) ObjectId object or a data object in
>> state NEW.
>>
>> The other interface is the "DataContextProvider" (single method:
>> getValidDataContext()).
>> The purpose is to provide the squeezer with a "valid" d.c. for the
>> current
>> thread.
>>
>> Once you've implemented the interfaces...
>>
>> If you're using tapestry 3.0.3, you'll have to subclass BaseEngine.
>> In your subclass, override createSqueezeAdapter with something like:
>>
>> ISqueezeAdaptor[] adapters = {
>> new DataObjectAdaptor(new DataContextProviderImp(), new
>> ObjectIdStorageProviderImp())
>> };
>> return new DataSqueezer(getResourceResolver(), adapters);
>>
>>
>> If you're using tapestry 4.0.beta-xxx, then you can skip the
>> subclassing
>> and just define the adapter in your hivemind config file.
>> There are many examples of how to do this posted throughout
>> the userlist archives, and I believe on the tapestry wiki, as well.
>>
>> Robert
>>
>> jaka lustek wrote:
>>
>>
>>> Hi,
>>>
>>> I posted similar question on Tapestry list, but did not get the answer
>>> so far. Can someone explain the steps to use CayenneDataSqueezer with
>>> Tapestry. I downloaded the squeezer from Tassel. I don't want to go
>>> statefull, is it possible to achieve this with CayenneSqueezer? I
>>> hope I
>>> am not asking silly questions.
>>>
>>> I have a tiny web app, just two pages, the first is collecting answers
>>> with radio group buttons, and the second is collecting user data. The
>>> model will use some three tables and some relationships. Simple model,
>>> simple web app, but as I am new to Cayenne Tapestry world I need some
>>> hints. I intend to present this app in my company as a proof of
>>> concept
>>> when will be ready (and this shold happen very soon).
>>>
>>> Thanks,
>>> Borut
>>>
>>> ____________________
>>> http://www.email.si/
>>>
>>>
>>>
>>
>
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