If you did that displaytag would be acting as the MVC, not Struts.
The logic you want to put into your DataSet belongs in the Action. What
is preventing that is displaytag likes to choose random unique identifiers
for parameters, making it pretty much impossible to have Struts populate
an ActionForm for you.
The Struts Action should be getting a sorted page of information from the
persistence layer and exposing only that page to displaytag.
What is missing is a way to make displaytag call your Action in an
intuitive way when the user clicks a sort button, or a page number. The
random integer is there to allow mutiple tables on the samge page. But an
alternative approach would be to have properties defining the paramId for
page, sort column and sort order.
But displaytag is set up to do this all internally, so I imagine it wont
be a simple matter of adding a few more properties to the tld. Someone
spoke earlier of the problem of having modle and view integrated and I
think this is a pretty good example of how it makes it tough to extend.
> well, the way i invision it is that for each type of table, you'd
> implement
> a DataSet. obviously, if the data is coming out of a database, it will be
> entirely dependent on what db you're using and what your table structure
> is.
>
> think of it like this (i use struts, so this will be in struts
> terminology,
> but the idea applies for any MVC framework).
>
> in your action, you find out which type of data the user wants, say
> they're
> looking for red widgets. you instantiate a object that implements DataSet.
> you can construct it in some way that it knows to search for red widgets,
> for examples DataSet ds = new MyDataSet(ProductType.WIDGET,
> ProductVariant.RED);
>
> then you stick that object in the request scope [
> request.setAttribute("ds",
> ds); ], and forward to your view. then in the view you have your
> displaytag:
>
> <display:table name="ds"> ... </display:table>
>
> in the TableTag class, it would tell the DataSet what the sort and paging
> is. then it calls DataSet.getHtmlData(), and then at that point, the
> DataSet
> will go out to the database and fetch the data.
>
>
> so you'd have different DataSets for different tables, all they would know
> how to do is fetch some data that they were told to fetch given a sort and
> page.
>
> --alex
>
>> Date: Fri, 16 Apr 2004 12:09:55 -0400 (EDT)
>> From: John York <[EMAIL PROTECTED]>
>> To: "[EMAIL PROTECTED]"
>> <[EMAIL PROTECTED]>
>> Subject: Re: [displaytag-devel] Accepting large datasets (was:
>> why iterator
>> over undisplayed rows?)
>> Reply-To: [EMAIL PROTECTED]
>>
>> This sounds like a good idea. I've been thinking about various ways to
>> implement this as well. I think I agree with most of this. I
>> think that if
>> we made the DataSet object implement the Iterator interface, we could
>> encapsulate all the database paging/sorting code in that object, and the
>> TableTag still just treats it as an Iterator, which would mean very
>> minimal changes to the existing code.
>>
>> The only problem I see with this approach is that the implementation
>> will
>> be tied to the database you are using. Each database may handle
>> paging/sorting differently, so that will need to be taken into account.
>> Maybe what you end up doing is creating a set of DatabaseDriver classes,
>> that could control any of the per-database oddities. You could try
>> sticking to the SQL spec, but there will always be more efficient ways
>> to
>> perform these operations with database-specific addons.
>>
>> I'd still like to split out the different functionalites of this tag
>> into
>> at least 3 or 4 groups:
>>
>> 1. displaying data
>> 2. paging data
>> 3. sorting data
>> 4. decorating data
>>
>> If we could do this, then each piece could be extended for user-specific
>> things, and we could provide all the common things with the binary
>> distribution.
>>
>> Just my $.02 as always...
>>
>> John
>>
>
>
>
>
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