RE: [INTERFACES] query java object?
От | Peter Mount |
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Тема | RE: [INTERFACES] query java object? |
Дата | |
Msg-id | 1B3D5E532D18D311861A00600865478C70C05F@exchange1.nt.maidstone.gov.uk обсуждение исходный текст |
Список | pgsql-interfaces |
Comments prefixed with PM: -- Peter Mount Enterprise Support Maidstone Borough Council Any views stated are my own, and not those of Maidstone Borough Council. -----Original Message----- From: Joe Shevland [mailto:shevlandj@kpi.com.au] Sent: Friday, January 07, 2000 6:45 PM To: Peter Mount; 'Phillip Rhodes'; 'pgsql-interfaces@postgresql.org' Subject: Re: [INTERFACES] query java object? Hi all, OK, hopefully this all makes sense... <background> The enterprise java beans spec specifies that classes requiring (CMP) persistence need to let the container know which attributes to persist by way of an XML descriptor. </background> So, given that we only want to persist certain properties/attributes of a particular Java class is this possible using the mechanism described below? Also, what are the overheads involved here? I guess the table will need to be created the first time an object of a particular type is stored, after that it should fairly normal? PM: Our existing model is based around Serializable rather than Enterprise Java Beans, but yes, it includes a static create() method which will parse the class (and sub-classes), and creates one or more tables ready to store the objects. It doesn't create any indices (yet). I'd love to be able to come up with a container-managed-persistence module based on PostgreSQL for EJBOSS (www.ejboss.org), but I'm still sorting things out in my head as to the best ways of doing this. PM: I haven't looked at Enterprise Java Beans before (mainly because I haven't needed to), but I don't see why we can't support them in a similar manner to Serializable classes. One little weird one, given that the Java classes you persist actually persist other classes they reference (as long as they're defined in PostgreSQL mapping I guess), would a way around the cyclic reference problem be to check the .equals() method when storing chained objects, maintain a hashtable for each root node and not store the object if it has already been done? That seems awfully simplistic, what are the issues involved? PM: This is a problem with our Serialize class. I wonder how Sun handle this with Serialized objects? Regards, Joe. ----- Original Message ----- From: "Peter Mount" <petermount@it.maidstone.gov.uk> To: "'Phillip Rhodes'" <rhodespc@bellatlantic.net>; "'pgsql-interfaces@postgresql.org'" <pgsql-interfaces@postgreSQL.org> Sent: Thursday, January 06, 2000 1:50 AM Subject: RE: [INTERFACES] query java object? > Yes of sorts. We have a small extension that allows a Serialized object > to be stored in one or more tables (rather than as a stream). Once > serialized in this way, you can then query the stored objects just like > any other SQL Table. > > Peter > > -- > Peter Mount > Enterprise Support > Maidstone Borough Council > Any views stated are my own, and not those of Maidstone Borough Council. > > > > -----Original Message----- > From: Phillip Rhodes [mailto:rhodespc@bellatlantic.net] > Sent: Monday, January 03, 2000 2:11 AM > To: 'pgsql-interfaces@postgresql.org' > Subject: [INTERFACES] query java object? > > > I read through the documentation for Postgres and Java, but I am a > little > unclear on something: (probably a few things!) > > Is it possible to execute a query based on the attributes of a > serialized > object? Or do I have to instantiate each object and do an if test? > > > Thanks! > > Phillip > > > > ************ > > ************ >
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