Note that just because there are multiple data contexts doesn't mean
you can't share the object cache. By default, they are shared across
the application. A data context is typically a subset of your total
fetched objects -- those which are you are making specific changes to
as a group.
http://cayenne.apache.org/doc30/caching-and-fresh-data.html
http://cayenne.apache.org/doc30/individual-object-caching.html
Also, using a per-session datacontext isn't the "right way". It's
just one of many ways. I've used per-request data contexts, and even
per-method data contexts. It mostly depends on the length of the
scope of your database operations -- when you start modifying the data
and when you commit it. You'll want your data context to live for
however long that length of time is.
On Sat, May 22, 2010 at 7:50 AM, Michael Gentry <mgentr..asslight.net> wrote:
> Hi Davide,
>
> 1) Unless your application is read-mostly, and it doesn't sound like it is,
> you'll want separate DataContexts per user to track their individual changes
> in distinct DataContexts. Otherwise the changes will get co-mingled and
> chaos likely will ensue.
>
> 2) You should be fine, but you can always fine-tune later if required by
> kicking objects out of the DataContext yourself where it makes sense. I'd
> optimize this later, though, as it may not be needed.
>
> mrg
>
>
> On May 22, 2010, at 5:03 AM, "mr.abanjo" <mr.abanj..mail.com> wrote:
>
>> Hi,
>> I'm developing a simple web application that store in a table an user
>> preference.
>> When a new user comes, i save a new record to a database using
>> datacontext:
>> *
>> *
>>
>> *datacontext.registerNewObject<http://cayenne.apache.org/doc30/api/org/apache/cayenne/access/DataContext.html#registerNewObject(java.lang.Object)>
>>
>> *(Object<http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html?is-external=true>
>> myobject);
>>
>> *datacontext.**commitChanges<http://cayenne.apache.org/doc30/api/org/apache/cayenne/access/DataContext.html#commitChanges()>
>> *();
>>
>> Cayenne perform an insert and all works fine.
>> I have 2 questions:
>>
>> 1) Reading the documentation the right way in a web application to create
>> a
>> datacontext is per session:
>> http://cayenne.apache.org/doc30/obtaining-datacontext.html
>> What happens if i treat it as a singleton? ( So i have one instance for
>> all
>> the users )
>>
>> 2) My web application has a high traffic, so i think that in a few time
>> i've
>> "registered" in datacontext thousands of record. This objects are
>> correctly
>> garbage collected or they stay in memory?
>> Reading the documentation:
>>
>> Since Cayenne 3.0, by default DataContext uses weak references to store
>> registered objects. So objects are allowed to be garbage collected by the
>> VM
>> if they are not referenced elsewhere in the application. "Elsewhere"
>> usually
>> means one of the following:
>>
>> - An object is directly or indirectly referenced by the application. [*NO
>> reference to them by any object in my application]*
>> - An object is a part of the cached query result stored by Cayenne. [*I
>> never configured cayenne for cache.. so if i'm not wrong, the default is
>> NO-CACHE]*
>> - An object is "dirty" (i.e. new, modified or deleted). In this case
>> Cayenne ensures that such object is retained at least until commit or
>> rollback. [*I perform always a commit after registering a new object]*
>>
>> So... i think that the memory should be correctly freed.
>>
>> N.B. I'm using Cayenne 3.0!
>>
>> Thanks for help!
>> Davide
>
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