Re: calling webservice only once from viewmodel

[Erik de Hair]

On 04/03/2015 09:03 AM, Erik de Hair wrote:


Then the question is how to hold that server-side state.  An HTTP 
Session
object is one option; the other is to store the data in the 
database.  That
basically means converting the view model into an entity (analogous to a
shopping cart entity); you could have some mechanism to clean up such
session entities after a day or two.
My architecture didn't work correctly. I tried to put the data in the 
memento as json-object but this way the memento got to big, and this 
gives persisting problems for the auditing/publishing services. Right 
now I'm putting the same data in the HTTP session and this works as it 
should be.

Thanks for your help,
Erik


Hope that helps provide some ideas...

Cheers
Dan

Hi Dan,

Thanks for your ideas. In the meantime I was changing the architecture 
of the view model calling the web service. I let the web service 
return a json string of al data to be returned and populate the 
datatables in the view model by reconstructing view models based on 
this json string contained in the view model memento.

The web service will now only be called by the action asking for web 
service parameters.

Erik

On 1 April 2015 at 11:33, Erik de Hair <e.deh...@pocos.nl> wrote:

On 03/27/2015 12:26 PM, Dan Haywood wrote:

Hi Erik,

On 25 March 2015 at 12:42, Erik de Hair <e.deh...@pocos.nl> wrote:

  Hi,
I have to call I web service from a view model but, when opening 
the view
model, the call to the web service is called twice. It doesn't 
matter if
the call is in de viewmodelinit or in some other method. May be 
there's
some way to track the state of the view model and let whether or 
not the
call is executed depend on that?

  My guess is that you are seeing the view model called twice 
because we
use
(Wicket's support for) the redirect-after-post pattern.

That is, when the action is invoked you are instantiating the view 
model
(which calls the webservice), and then we return a 302 redirect to the
browser so that it then re-requests the same URL, causing the view 
model
to
be recreated (and that webservice called).

Perhaps you could confirm if that's what's happening?

The following is happening...

In the initial state the view model is rendered and the data that is
needed to call the web service is already available from the view model
memento. (This means that when refreshing the page the web service 
will be
called again. This is not much of a problem.)

Now, when clicking** the action button that opens the action for
re-entering the web service parameters, a request for the view model is
done:

0:0:0:0:0:0:0:1 - - [01/Apr/2015:12:04:09 +0200] "GET
/portal/wicket/entity/*nl.pocos.dom.access.availability.PostalCodeCheck: 

PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPG1lbWVudG8-PGpzb24- 

eyJwb3N0YWxDb2RlIjoiNTYxNEFFIiwiaG91c2VOdW1iZXIiOiIxNTIifTwv
anNvbj48L21lbWVudG8-?6-1.IBehaviorListener.0-theme-entity-entity~0-
entityPropertiesAndCollections-entityProperties-leftColumn-
memberGroup-1-properties-4-property-scalarIfRegular-additionalLinks-
additionalLinkList-additionalLinkItem-0-additionalLink&_=1427882228283
HTTP/1.1" 200 12838 http-bio-8081-exec-4 2303

This way the web service is called again because the previous web 
service
parameters are still available from the view model memento.

After submitting the following requests are handled:

0:0:0:0:0:0:0:1 - - [01/Apr/2015:12:06:17 +0200] "POST
/portal/wicket/entity/*nl.pocos.dom.access.availability.PostalCodeCheck: 

PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPG1lbWVudG8-PGpzb24- 

eyJwb3N0YWxDb2RlIjoiNTYxNEFFIiwiaG91c2VOdW1iZXIiOiIxNTIifTwv
anNvbj48L21lbWVudG8-?6-1.IBehaviorListener.1-theme-
actionPromptModalWindow-content-parameters-inputForm-okButton HTTP/1.1"
200 91 http-bio-8081-exec-6 169

(web service called two times during this request)

0:0:0:0:0:0:0:1 - - [01/Apr/2015:12:06:19 +0200] "GET
/portal/wicket/wicket/page?7 HTTP/1.1" 200 167629 
http-bio-8081-exec-6 2582

(web service called once during this request)

If it is, then one option might be to defer the fetching of the 
data until
as late as possible, ie when it needs to be constructed.

I tried this but the method that exposes the data to the gui will 
always
call the method that fetches the data when constructing the view 
model. So
no matter how late the data will be fetched, it will always be fetched.

Another option might be to have the view model use the HttpSession 
(via
isis-module-servletapi addon) to keep track of state.

I'm still using Isis 1.7.0 and Eclipse complains about the module 
missing
some dependency. It does work however and I can prevent the web service
from being called by checking for a request method of GET during the
POST-request but there are still 3 calls left.

I didn't use the session object yet. Will try that.


HTH
Dan



  The web service is fetching data, triggered by an action in the view
model, for the same view model. Do I always have to return a new view
model
with the fetched data in it or can I use the data from the fetch 
method
and
return the same view model?

Thanks,
Erik