Interesting that you mention Maps on queries, because I have another
proposal.
The example says all:
<example>
Map result = (Map) pm.newQuery("SELECT new Map<name,this> FROM
Person").execute();
result.get("jordan") returns Person[name=jordan,firstName=michael]
result.get("simpson") returns [ Person[name=simpson,firstName=bart],
Person[name=simpson,firstName=homer] ]
</example>
That means, the query is actually not run when query.execute() is invoked,
but on each operation over the returned map.
The map instance returned, is a 2 layers map:
1-entries fetch from database (datastore entries)
2-entries added via map.put or already loaded from db (local entries)
Below I describe the contract for the Map instance returned:
Map.size()
When a transaction is active and query not closed: Delegates to JDO
implementation, that ultimately performs a SELECT COUNT(*) in SQL databases.
The local entries are intersected with the SELECT COUNT(*) entries. The
intersection count will be the size() return value.
Otherwise: Performs a size() over the local entries.
Map.put()
Put a new entry to the local map entries. Not persisted.
Map.remove()
Remove the entry from the local map entries. Not removed from database.
Map.get()
When a transaction is active and query not closed: First checks local cache,
if found return, otherwise fetch entries from the datastore and add to the
local entries.
Otherwise: Performs a get() over the local entries.
When a PM or Query is closed, the map is disconnected and only the local
entries will remain in the hash map.
I'm not going any further, before your feedback.
Cheers,
-----Message d'origine-----
De : Matthew Adams [mailto:[EMAIL PROTECTED]
Envoyé : mardi 30 octobre 2007 19:09
À : Apache JDO project; JDO Expert Group
Objet : #key and #value in query filter?
Hi all,
I just proposed in JPA on the thread for support for Maps that JPAQL
support "#key" and "#value" for navigation through maps, much like we
can use "#key" and "#value" to define fetch groups in JDO. I took
for granted that these expressions can be used in JDOQL, and after a
search through the spec, I don't see where they can. I only see the
list of supported Map and Collection methods in 14.6.2, "Filter
specfication".
One of the JPA examples in the proposal looks like the following:
SELECT im#value
FROM Item i JOIN i.images im
WHERE im#key in ('thumbnail', 'full', 'high-res')
First, what would the equivalent JDOQL for this be?
Second, what are your thoughts on JDOQL support for "#key", "#value"
and "in"? This would allow us to write the following. This is
decidedly not very Java-like (a design goal of JDOQL), so this would
be a bit of a departure from tradition for JDOQL.
-matthew
