␡
- Quick Intro to JDO
- The Problem at Hand
- Persisting the Objects
- Retrieving the Objects
- The Wrap-Up
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Retrieving the Objects
To find our objects, we need to use JDOQL, JDO's query language; it's a bit like a clumsy mix of SQL and Java. JDOQL queries are run through a Query object, as shown in the persistQuoteSource method in Listing 4. What we want to do is pull all quotes from a specific QuoteSource that contain a certain bit of text. Unfortunately, JDOQL's ability to query based on string logic is rather limited, so we'll do this in two steps:
Ask the user which source of all the available sources to search, and pull all associated quotes into memory.
Use non-JDO methods to whittle down that list.
First, the code to pull all the applicable quotes from a QuoteSource (see Listing 6):
Listing 6 Retrieving all QuoteInfos for a particular QuoteSource
protected List getAllQuotesFromSource(QuoteSource source) throws Exception
{
Query query = null;
List list = new ArrayList();
try
{
query = getPM().newQuery(
QuoteInfo.class,
"source == param");
query.declareParameters("QuoteSource param");
query.setOrdering("lineNumber ascending");
list.addAll((Collection)query.execute(source));
query.closeAll();
} catch(Exception e)
{ throw new Exception("Error querying for quotes by source: " + e); }
return list;
}
Next, the code to trim that list based on a string from user input (see Listing 7):
Listing 7 Filtering the list of QuoteInfos
protected List filterQuotes(List quotes, String test)
{
List returnList = new ArrayList();
QuoteInfo currQuoteInfo = null;
for(int i = 0; i < quotes.size(); ++i)
{
currQuoteInfo = (QuoteInfo)quotes.get(i);
if(currQuoteInfo.matches(test))
returnList.add(currQuoteInfo);
}
return returnList;
}