This one time, at band camp, Steffen Fiedler said:
SF>
SF>"Bruce Snyder" <[EMAIL PROTECTED]> wrote:
SF>
SF>> This one time, at band camp, Steffen Fiedler said:
SF>>
SF>> SF>Hi,
SF>> SF>
SF>> SF>I have an application that works with objects, that are linked in many
SF>> SF>ways among each other.
SF>> SF>What is the best way to save them?
SF>> SF>I try to to it by long transactions, because the Objects are used while
SF>> SF>the whole application
SF>> SF>and and i don't want to hold one transaction all the time to hold them
SF>> SF>persistent.
SF>> SF>Its a multi-user web-application and i can't be sure, that the conection
SF>> SF>will be closed correctly.
SF>> SF>So i just open a connection, when some objects have to be
SF>> SF>read/saved/updated and want to
SF>> SF>save them by long transactions. When i do this:
SF>> SF>
SF>> SF>db.setAutoStore(false);
SF>> SF>db.begin();
SF>> SF>db.update(myObject);
SF>> SF>db.commit();
SF>> SF>
SF>> SF>i get the error:
SF>> SF>
SF>> SF>Commit failed: org.exolab.castor.jdo.TransactionAbortedException: Nested
SF>> SF>error:
SF>> SF>org.exolab.castor.jdo.PersistenceException: Object,
SF>> SF>com.sourcepark.ticketsystem.Ticket@305236,
SF>> SF>links to another object, com.sourcepark.ticketsystem.Priority@6a0105
SF>> SF>that is not
SF>> SF>loaded/updated/created in this transaction
SF>> SF>
SF>> SF>If i set db.setAutoStore(true) i get the error:
SF>> SF>
SF>> SF>Error while saving object:
SF>> SF>org.exolab.castor.jdo.DuplicateIdentityException: update object
SF>> SF>which is already in the transaction
SF>> SF>
SF>> SF>because i use some objects in many ways, i.e. the object 'state' can be
SF>> SF>a pre-state and a
SF>> SF>successor-state for another object and there are many other relations
SF>> SF>like this. I've tried
SF>> SF>to set the affected objects to access="read-only" in mapping.xml but
SF>> SF>without success.
SF>> SF>
SF>> SF>In the JDO-FAQ is written, that castor only supports bi-directional
SF>> SF>relationships, does
SF>> SF>that mean, if object1 contains a reference to object2, object2 should
SF>> SF>contain a vector
SF>> SF>of object1's?
SF>> SF>
SF>> SF>I expanded my mapping.xml, but now castor works very slowly, when i load
SF>> SF>a single
SF>> SF>user, the whole datamodel is loaded from DB cause all objects are linked
SF>> SF>among each other.
SF>> SF>Is it usefull to use castor for a web-application with complex
SF>> SF>datamodel? Whats about
SF>> SF>performance when there are many users and large databases. Could
SF>> SF>lazy-loading solve this
SF>> SF>problem?
SF>> SF>
SF>> SF>I've appended the whole mapping.xml for getting an impression about the
SF>> SF>object-structute.
SF>> SF>My main question is, if it's advisable to use castor for a multi-user
SF>> SF>web-application with
SF>> SF>such a datamodel and if yes, what is the most performance-friendly
SF>> SF>approach to save and
SF>> SF>load the objects.
SF>>
SF>> Steffen,
SF>>
SF>> I've found that Castor has it's limits with regards to very, very complex
SF>> object models. Much of my experience with this has been learned at my
SF>> day job where I work on a GIS application using highly complex data
SF>> in a highly complex object model (polygons, etc). BTW, I would NOT
SF>> consider your object model to be highly complex. Castor should handle
SF>> this just fine.
SF>>
SF>> I've also found that Castor does not enforce the bi-directional relations
SF>> at all times (as is stated in the JDO FAQ). This being said, I've used
SF>> Castor in the past with an object model similar to yours by not mapping
SF>> things bi-directionally. (This took some time to figure out because there
SF>> are situations where Castor wants a bi-directional mapping and other
SF>> situations where it doesn't matter (there are threads on the mailing
SF>> list discussing this, unfortunately I don't know the ins and outs of
SF>> this off the top of my head).) The situation to which I'm referring
SF>> was a mutli-user web app using long transactions. In this setting,
SF>> Castor performed just fine.
SF>>
SF>> Unfortunately I have no easy answer for this situation. However,
SF>> if you take the time to experiment with the removal of many of the
SF>> bi-directional references in your object model, I believe you'll start
SF>> to get the results you want.
SF>
SF>Ok thanks, i'll try a bit around.
SF>How can i avoid the Exception:
SF>"org.exolab.castor.jdo.DuplicateIdentityException: update object
SF>which is already in the transaction"
SF>while using long transactions? The affected objects don't have
SF>to be changed in this situation and read-only="true" doesn't
SF>change anything.
SF>The only way i found is to change objects by loading them and
SF>all there linked objects in short transactions.
SF>But i think, its not the best way...
Have you tried to use jdo.setAutoStore( true )? I'm curious to know how
that affects your situation.
Bruce
--
perl -e 'print unpack("u30","<0G)U8V4\@4VYY9&5R\"F9E<G)E=\$\!F<FEI+F-O;0\`\`");'
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