Ganesan.Sankara> I believe most of applications will have the following requirement:
Ganesan.Sankara>
Ganesan.Sankara> 1. Screen which fetches data from databases such as ORACLE
Ganesan.Sankara> 2. The screen has a limitation to show maximum number of records,
let's say
Ganesan.Sankara> 20.
Ganesan.Sankara> 3. The fetched rows exceed > 20. So the main screen shows a pointers
for
Ganesan.Sankara> page 1 , 2 , 3 ...
Ganesan.Sankara>
Ganesan.Sankara> To code this the developer has to write a cache function for each
screen
Ganesan.Sankara> and mechanism to store and retrieve. JDBC functions to skip result
set rows
Ganesan.Sankara> may not work since the query may be returning rows in random order.
Also
Ganesan.Sankara> the cache has to be designed in such a way it does not eat too much
memory.
Ganesan.Sankara>
Ganesan.Sankara> One of my projects , we did a slow cache with small memory foot
print. The
Ganesan.Sankara> main query will retrieve ROWIDs(ORACLE) and cache , each page hit will
Ganesan.Sankara> slice through ROWIDs cache and user ROWIDs to retrieve from ORACLE (
WHERE
Ganesan.Sankara> ROWID IN ( 'xx.xx.xx.xx','yy.yyy.yy.yy') ).
Ganesan.Sankara>
Ganesan.Sankara> If turbine includes a base class for the mulit-page screen it will
very
Ganesan.Sankara> useful. Is anyone out there has done any similar work??
I rewrote org.apache.turbine.util.db.LargeSelect for this purposes.
I splitted it to two classes and one interface:
LargeSelect - interacts with UI,
RecordFetcher - objects of this type do actual database operations,
RecordFetcherFactory - constructs RecordFetchers for different Object
database adapters( now for Castor only).
If you are interested in it I can put code on ftp.
Psevdocode of usage looks like this
For screen:
protected void doBuildTemplate( RunData data, WebContext context ) throws Exception
{
...
context.put("SelectResults", data.getUser().getTemp("selected_block"));
...
}
For action:
public void doQuery (RunData data, WebContext context) throws Exception
{
...
RecordFetcher fetcher = RecordFetcherFactory.createRecordFetcher(query,
bind_params);
LargeSelect sel = new LargeSelect("Select", fetcher, MEMORY_LIMIT, PAGE_SIZE);
data.getUser().setTemp("select", sel);
doNextchunk (data, context);
}
public void doAdd (RunData data, WebContext context) throws Exception
{
...
LargeSelect sel = (LargeSelect)data.getUser().getTemp("select");
sel.insertRecord(record);
doCurrentchunk(data, context);
}
public void doDelete (RunData data, WebContext context) throws Exception
{
...
LargeSelect sel = (LargeSelect)data.getUser().getTemp("select");
sel.deleteRecord(record_num);
doCurrentchunk(data, context);
}
public void doUpdate (RunData data, WebContext context) throws Exception
{
...
LargeSelect sel = (LargeSelect)data.getUser().getTemp("select");
sel.updateRecord(record_num, edited_record);
doCurrentchunk(data, context);
}
public void doNextchunk (RunData data, WebContext context) throws Exception
{
LargeSelect sel = (LargeSelect)data.getUser().getTemp("select");
if (sel.isLastBlock())
data.setMessage("No more results for this query.");
else
data.getUser().setTemp("selected_block", sel.getNextResults());
}
public void doPrevchunk (RunData data, WebContext context) throws Exception
{
LargeSelect sel = (LargeSelect)data.getUser().getTemp("select");
if (sel.isFirstBlock())
data.setMessage("At first record.");
else
data.getUser().setTemp("selected_block", sel.getPreviousResults());
}
public void doFirstchunk (RunData data, WebContext context) throws Exception
{
LargeSelect sel = (LargeSelect)data.getUser().getTemp("select");
data.getUser().setTemp("selected_block", sel.getResults(0));
}
public void doCurrentchunk (RunData data, WebContext context) throws Exception
{
LargeSelect sel = (LargeSelect)data.getUser().getTemp("select");
data.getUser().setTemp("select_block", sel.getCurrentResults());
}
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