Yeah, so what you're proposing is completely different... Please
start a different thread on that.
WRT this thread, which is a discussion on how to support something
less verbose and complicated than what JDOQL currently requires to
support this. What I'm seeing in JDOQL right now with regard to
querying through keys and values in Maps is not a simple as what I'm
seeing in JPAQL.
Is there some way to make querying through Map keys and values simpler?
-matthew
On Oct 30, 2007, at 1:37 PM, Erik Bengtson wrote:
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
