BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Object liberation and persistence layers          BorlandTalk.com Forum Index -> Delphi OO design View previous topic :: View next topic   Author Message Gabriel GIbaut Guest Posted: Mon Jan 17, 2005 6:59 pm    Post subject: Object liberation and persistence layers Hello, I need some pointers about persistence layers. All the information i´ve found is about mapping, cacheing and persisting objects to the database. But what about freeing the objects? Who is responsible for this? (The programmer?)What if you have a cache? (is the persistence layer responsible then?) Are there well known strategies to deal with this subject? Any info on persistence layers would be appreciated. Gabriel Back to top Jim Cooper Guest Posted: Mon Jan 17, 2005 7:17 pm    Post subject: Re: Object liberation and persistence layers Quote: But what about freeing the objects? Who is responsible for this? (The programmer?) In Win32. In .NET you can let the GC take care of it. Quote: What if you have a cache? (is the persistence layer responsible then?) Yes, but you need to track usage somehow still in Win32. in .NET you may have the opposite problem, in that you need to keep a reference alive to all objects in the cache, or they'll disappear occasionally :-) Cheers, Jim Cooper _______________________________________________ Jim Cooper [email]jim (AT) falafelsoft (DOT) com[/email] Falafel Software http://www.falafelsoft.com _______________________________________________ Back to top Gabriel GIbaut Guest Posted: Mon Jan 17, 2005 7:20 pm    Post subject: Re: Object liberation and persistence layers I forgot to mention, i´m working with D7 Thanks Gabriel "Jim Cooper" <jim (AT) falafelsoft (DOT) com> escribió en el mensaje news:41ec0f64$1 (AT) newsgroups (DOT) borland.com... Quote: But what about freeing the objects? Who is responsible for this? (The programmer?) In Win32. In .NET you can let the GC take care of it. What if you have a cache? (is the persistence layer responsible then?) Yes, but you need to track usage somehow still in Win32. in .NET you may have the opposite problem, in that you need to keep a reference alive to all objects in the cache, or they'll disappear occasionally :-) Cheers, Jim Cooper _______________________________________________ Jim Cooper [email]jim (AT) falafelsoft (DOT) com[/email] Falafel Software http://www.falafelsoft.com _______________________________________________ Back to top Marc Rohloff [TeamB] Guest Posted: Mon Jan 17, 2005 8:53 pm    Post subject: Re: Object liberation and persistence layers On Mon, 17 Jan 2005 15:59:52 -0300, Gabriel GIbaut wrote: Quote: But what about freeing the objects? Who is responsible for this? (The programmer?)What if you have a cache? (is the persistence layer responsible then?) Are there well known strategies to deal with this subject? This is the advantage of interfaces since they are reference counted they handle this more or less automatically. -- Marc Rohloff [TeamB] marc rohloff -at- myrealbox -dot- com Back to top Peter Morris [Droopy eyes Guest Posted: Mon Jan 17, 2005 9:07 pm    Post subject: Re: Object liberation and persistence layers Bold always references objects via an ObjectLocator. If you ask for an object the locator will load it. Each time you read/write an attribute / association of the object an internal "last touched" datetime stamp is updated for the object. You can then have an object unloader component. Tell it to run every 5 minutes, unloading any objects which haven't been touched for 15 minutes (for example). -- Pete ==== ECO Modeler, Audio compression components, DIB graphics controls, FastStrings http://www.droopyeyes.com Read or write articles on just about anything http://www.HowToDoThings.com My blog http://blogs.slcdug.org/petermorris/ Back to top Jim Cooper Guest Posted: Mon Jan 17, 2005 9:50 pm    Post subject: Re: Object liberation and persistence layers Quote: I forgot to mention, i´m working with D7 OK. Then see Marc's and Peter's replies for some different strategies. Cheers, Jim Cooper _______________________________________________ Jim Cooper [email]jim (AT) falafelsoft (DOT) com[/email] Falafel Software http://www.falafelsoft.com _______________________________________________ Back to top Bob Dawson Guest Posted: Tue Jan 18, 2005 1:08 am    Post subject: Re: Object liberation and persistence layers "Gabriel GIbaut" wrote Quote: objects to the database. But what about freeing the objects? Who is responsible for this? (The programmer?)What if you have a cache? (is the persistence layer responsible then?) Are there well known strategies to deal with this subject? There are several approaches. I do use a cache so I'll describe that briefly. Basically the object service layer maintains a ref-counted list of all active business objects. When an application programmer requests an object myObj := TSomeBizObject.BOCreate(14); //a class function, not a constructor what happens is the class function forwards the request to the object service layer that layer searches the active objects list by class and instance ID to see if the object already exists in memory. If it does, a reference is returned and the refcount incremented. if not, the request is forwarded to the data service layer, which searches all current datasets in memory to see if the object can be instantiated based on current information. If so, this is done, the object is entered into the active objects list, which returns a reference to this object as before if not, the request is forwarded to the persistence layer and an SQL call is issued to retrieve the object's information. The object is then built from this dataset (which is then discarded) and then returned as before. The the programmer releases the object this call is also fowarded to the object service layer active object list, which decriments the refcount and decides whether to free the object accordingly. Quote: Any info on persistence layers would be appreciated. Here are some starting places: Brown, Philip. "An Object Oriented Persistence Layer Design." Philip published a series of introductory articles in the late EXE magazine (UK). These are available from the Borland Community CodeCentral website, in the category "Best Techniques / Delphi", submission #15511. Ambler, Scott. http://www.ambysoft.com/ Has many interesting pieces in the online white papers section, including a paper containing a general class model for a complete persistence layer: "Design of a Robust Persistence Layer for Relational Databases." Carter, Joanna. http://www.carterconsulting.org.uk See her four-part "Keeping Hold of Your Things" article, and the link to "A Series of Articles on Object Persistence." Fowler, Martin. http://www.martinfowler.com/. From his main site, use the "Articles" link at the top of the page. From the articles page see the pieces "Separating User Interface Code" and "Reducing Coupling." bobD Back to top Gabriel GIbaut Guest Posted: Wed Jan 19, 2005 6:54 pm    Post subject: Re: Object liberation and persistence layers Thanks eveyone for their response. Gabriel "Bob Dawson" <RBDawson (AT) prodigy (DOT) net> escribió en el mensaje news:41ec68c4 (AT) newsgroups (DOT) borland.com... Quote: "Gabriel GIbaut" wrote objects to the database. But what about freeing the objects? Who is responsible for this? (The programmer?)What if you have a cache? (is the persistence layer responsible then?) Are there well known strategies to deal with this subject? There are several approaches. I do use a cache so I'll describe that briefly. Basically the object service layer maintains a ref-counted list of all active business objects. When an application programmer requests an object myObj := TSomeBizObject.BOCreate(14); //a class function, not a constructor what happens is the class function forwards the request to the object service layer that layer searches the active objects list by class and instance ID to see if the object already exists in memory. If it does, a reference is returned and the refcount incremented. if not, the request is forwarded to the data service layer, which searches all current datasets in memory to see if the object can be instantiated based on current information. If so, this is done, the object is entered into the active objects list, which returns a reference to this object as before if not, the request is forwarded to the persistence layer and an SQL call is issued to retrieve the object's information. The object is then built from this dataset (which is then discarded) and then returned as before. The the programmer releases the object this call is also fowarded to the object service layer active object list, which decriments the refcount and decides whether to free the object accordingly. Any info on persistence layers would be appreciated. Here are some starting places: Brown, Philip. "An Object Oriented Persistence Layer Design." Philip published a series of introductory articles in the late EXE magazine (UK). These are available from the Borland Community CodeCentral website, in the category "Best Techniques / Delphi", submission #15511. Ambler, Scott. http://www.ambysoft.com/ Has many interesting pieces in the online white papers section, including a paper containing a general class model for a complete persistence layer: "Design of a Robust Persistence Layer for Relational Databases." Carter, Joanna. http://www.carterconsulting.org.uk See her four-part "Keeping Hold of Your Things" article, and the link to "A Series of Articles on Object Persistence." Fowler, Martin. http://www.martinfowler.com/. From his main site, use the "Articles" link at the top of the page. From the articles page see the pieces "Separating User Interface Code" and "Reducing Coupling." bobD Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         BorlandTalk.com Forum Index -> Delphi OO design All times are GMT Page 1 of 1   Jump to: Select a forum C++ Builder Newsgroups----------------C++ BuilderC++ Builder (ActiveX)C++ Builder (Announcements)C++ Builder (Command Line Tools)C++ Builder DatabasesC++ Builder Databases (ADO)C++ Builder Databases (Desktop)C++ Builder Databases (InterBase Express)C++ Builder Databases (Multi-Tier)C++ Builder Databases (SQL Servers)C++ Builder (Graphics)C++ Builder (IDE)C++ Builder (Internet)C++ Builder (Internet Socket)C++ Builder (Internet Web)C++ Builder (Jobs)C++ Builder (Language)C++ Builder (Language C++)C++ Builder (Compatibility with MFC)C++ Builder (Native API)C++ Builder (Non-Technical)C++ Builder (Students)C++ Builder (Third Party Tools)C++ Builder (Upgrade)C++ Builder (VCL)C++ Builder (VCL Components Usage)C++ Builder (VCL Components Development)C++ Builder (VCL Usage)C++ Builder (WinAPI)C++ Builder Installation Delphi Newsgroups----------------Delphi (General)Delphi ActiveX Controls UsageDelphi ActiveX Controls DevelopmentDelphi As400Delphi DatabasesDelphi Databases (ADO)Delphi Databases (dbExpress)Delphi Databases (Desktop)Delphi Databases (InterBase Express)Delphi Databases (Multi-Tier)Delphi Databases (SQL Servers)Delphi DeploymentDelphi GraphicsDelphi IDEDelphi InternationalizationDelphi InternetDelphi Internet Isapi-WebBrokerDelphi Internet WebSnapDelphi Internet WinsockDelphi JobsDelphi Language BASMDelphi Language ObjectPascalDelphi Model Driven Architecture (General)Delphi Model Driven Architecture (Third Party)Delphi MultimediaDelphi Native APIDelphi Non-TechnicalDelphi ObjectPascalDelphi OLE AutomationDelphi OO designDelphi OpenToolsAPIDelphi Reporting-ChartingDelphi RTLDelphi StudentsDelphi TeamSourceDelphi Thirdparty ToolsDelphi Thirdparty Tools (General)Delphi Thirdparty Tools (IntraWeb)Delphi Thirdparty Tools (RaveReports)Delphi UpgradeDelphi VCLDelphi VCL ComponentsDelphi VCL Components UsingDelphi VCL Components WritingDelphi WebServices SOAPDelphi WinAPIDelphi XMLDelphi Installationcomp.lang.pascal.delphi.components.misccomp.lang.pascal.delphi.components.usagecomp.lang.pascal.delphi.components.writingcomp.lang.pascal.delphi.databasescomp.lang.pascal.delphi.misccomp.sources.delphi JBuilder Newsgroups----------------JBuilderJBuilder AnnouncementsJBuilder Applet IssuesJBuilder As400JBuilder CompilerJBuilder CORBA/RMIJBuilder DatabasesJBuilder DB SwingJBuilder DebuggerJBuilder DeploymentJBuilder DocumentationJBuilder EnterpriseJBuilder HandheldJBuilder IDEJBuilder JavaJBuilder JavaAPIJBuilder Java LanguageJBuilder Java SwingJBuilder Java BeansJBuilder Java Beans UsageJBuilder Java Beans DevelopmentJBuilder JBCLJBuilder JDataStoreJBuilder JobsJBuilder LinuxJBuilder MacintoshJBuilder & MobileSetJBuilder MultiLingual AppsJBuilder Non-TechnicalJBuilder OpenToolsJBuilder Servlets (JSP)JBuilder StudentsJBuilder Team DevelopmentJBuilder Thirdparty ToolsJBuilder UpgradeJBuilder Installation InterBase Newsgroups----------------InterBaseInterBase Bug DiscussionInterBase GeneralInterBase IBConsoleInterBase OpenSourceInterBase ReplicationInterBase SQLInterBase ThirdpartyInterBase Installation Miscellaneous Borland Newsgroups----------------AppCenterAppServerEnteraVisiBroker  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.