[flexcoders] Re: Flex + Spring + Hibernate - Lazy=true
hi, these problems caused mainly by AMF3 which is quite low level and sessionless. as i understand AMF3, it uses references for these objects only that are in the same request, so it assumes that neither server nor client remembers what objects were already sent. that's the main problem - just having this session aware protocol implemented will make all communication lazy by default. (in addition, it would be nice to be able to control how deeply object graph should be serialized for each particular request) regards, Andrii Olefirenko --- In flexcoders@yahoogroups.com, Jeff Vroom [EMAIL PROTECTED] wrote: We haven't released the source for blazeds yet but it is coming. It does not contain any AS source generation but I think that is easy to layer on and there are a bunch of decent implementations out there. There is better support for customizing the serialization process in blazeds (improved over 2.5.1). The beta for blazeds has some of this but we are adding even more between beta and the release. Implementing lazy loading is a bit of a pain with hibernate if you have to do it using remote object. There are two major issues: 1) the class names of the generated wrapper classes used by hibernate mess up the mapping of the class names used to find the right AS class. This one is easy to get around with this PropertyProxy mechanism. In fact, LC DS contains the source to a PropertyProxy implementation (HibernatePropertyProxy.java) which you can use with remote object to strip the generated class name off before serialization. This has the side effect of returning empty versions of all non-loaded lazy properties which brings us to problem 2). Note that hibernate has different mechanisms for doing the lazy loading.. it can do byte code modification but I haven't used that technique so I'm not sure how it works here. 2) If you did not fetch a property with lazy=true in hibernate before the session is closed, the attempt to access that property during serialization fails with the session closed error. To get around this, you can make sure you access all properties you need before the serialization.. this is the approach used by LC DS but because it has a model of the association properties, you don't have to code it up yourself. It is done by the assembler so it is automatic.Another hacky approach is to put a servlet filter in which opens up a hibernate session before calling the MessageBrokerServlet, then close the session once it returns. That means you lose control over the hibernate sessions in your application and you have a transaction which is open for the entire duration of the request which is not very flexible. There might also be performance problems if you have a session/transaction open while you are doing I/O. Not sure that will be a problem but these are the reasons we went with the prefetch mechanism in LC DS's hibernate assembler. In terms of the issues with hibernate in 2.5 and earlier versions, one of the trickiest things is that you need to make your data-management-config.xml match up with the hibernate config. We're hoping to get a chance into a future version which makes this not necessary since the configs are pretty similar. You also need to do the AS code which matches the Java code yourself (or use a 3rd party code gen tool). Jeff From: flexcoders@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of andrii_olefirenko Sent: Friday, January 11, 2008 5:46 PM To: flexcoders@yahoogroups.com Subject: [flexcoders] Re: Flex + Spring + Hibernate - Lazy=true Assemblers are more for CRUD apps. And even with Hibernate assembler, i haven't achieved lazy loading (it was old version of FDS and maybe i didn't try hard but anyway). If anyone has been able to implement lazy loading with LCDS 2.5, let me know so at least i will be assured that this is possible :) in addition to lazy loading, there are also problems of multiple instances if the same object, and the need to manually write actionscript counterparts of java objects. IFAIK, there no tool for automated generation AS3 classes out of java classes in BlazeDS. For big projects with permanent changes to the objects it is pain to manually maintain both AS3 and java obejcts sync. it would be nice to implement all these features in open-sourced BlazeDS, but i didn't find any source code in distribution as for now. --- In flexcoders@yahoogroups.com mailto:flexcoders%40yahoogroups.com , Rodrigo Pereira Fraga rpffoz@ wrote: Oh my god =/ But who uses the LCDS, it does not contain a HibernateAssembler which implements the use of lazy? --- In flexcoders@yahoogroups.com mailto:flexcoders%40yahoogroups.com , andrii_olefirenko andriyo@ wrote: BlazeDS (and LCDS as far as i remember) doesn't support this out of box
[flexcoders] Re: Flex + Spring + Hibernate - Lazy=true
Check Granite Data Services. They handle lazy loading properties support, they have as3 code generator. Den
[flexcoders] Re: Flex + Spring + Hibernate - Lazy=true
BlazeDS (and LCDS as far as i remember) doesn't support this out of box. There are workarounds like 1) make you own DTO (hibernate free) 2) prefetch object dependencies 3) include metadata about lazy properties with you objects, control externalization to handle objects with metadata and so on. if you develop with Hibernate (or EJB3), lack of lazy object support makes BlazeDS simply unusable for real enterprise application devs. --- In flexcoders@yahoogroups.com, Rodrigo Pereira Fraga [EMAIL PROTECTED] wrote: Someone has some solution to use the Pattern OpenSessionInView with Flex using BlazeDS? I am using Spring and it contains a OpenSessionInViewFilter used in web.xml, and a OpenSessionInViewInterceptor. But it is different with Flex +) Someone has idea of how I can use the Lazy = true to hibernate with the Flex + Spring? Atenciosamente: --- | Rodrigo Pereira Fraga | http://www.digows.com e-mails: [EMAIL PROTECTED] [EMAIL PROTECTED] ---
[flexcoders] Re: Flex + Spring + Hibernate - Lazy=true
Oh my god =/ But who uses the LCDS, it does not contain a HibernateAssembler which implements the use of lazy? --- In flexcoders@yahoogroups.com, andrii_olefirenko [EMAIL PROTECTED] wrote: BlazeDS (and LCDS as far as i remember) doesn't support this out of box. There are workarounds like 1) make you own DTO (hibernate free) 2) prefetch object dependencies 3) include metadata about lazy properties with you objects, control externalization to handle objects with metadata and so on. if you develop with Hibernate (or EJB3), lack of lazy object support makes BlazeDS simply unusable for real enterprise application devs. --- In flexcoders@yahoogroups.com, Rodrigo Pereira Fraga rpffoz@ wrote: Someone has some solution to use the Pattern OpenSessionInView with Flex using BlazeDS? I am using Spring and it contains a OpenSessionInViewFilter used in web.xml, and a OpenSessionInViewInterceptor. But it is different with Flex +) Someone has idea of how I can use the Lazy = true to hibernate with the Flex + Spring? Atenciosamente: --- | Rodrigo Pereira Fraga | http://www.digows.com e-mails: rpffoz@ rfraga@ ---
[flexcoders] Re: Flex + Spring + Hibernate - Lazy=true
Assemblers are more for CRUD apps. And even with Hibernate assembler, i haven't achieved lazy loading (it was old version of FDS and maybe i didn't try hard but anyway). If anyone has been able to implement lazy loading with LCDS 2.5, let me know so at least i will be assured that this is possible :) in addition to lazy loading, there are also problems of multiple instances if the same object, and the need to manually write actionscript counterparts of java objects. IFAIK, there no tool for automated generation AS3 classes out of java classes in BlazeDS. For big projects with permanent changes to the objects it is pain to manually maintain both AS3 and java obejcts sync. it would be nice to implement all these features in open-sourced BlazeDS, but i didn't find any source code in distribution as for now. --- In flexcoders@yahoogroups.com, Rodrigo Pereira Fraga [EMAIL PROTECTED] wrote: Oh my god =/ But who uses the LCDS, it does not contain a HibernateAssembler which implements the use of lazy? --- In flexcoders@yahoogroups.com, andrii_olefirenko andriyo@ wrote: BlazeDS (and LCDS as far as i remember) doesn't support this out of box. There are workarounds like 1) make you own DTO (hibernate free) 2) prefetch object dependencies 3) include metadata about lazy properties with you objects, control externalization to handle objects with metadata and so on. if you develop with Hibernate (or EJB3), lack of lazy object support makes BlazeDS simply unusable for real enterprise application devs. --- In flexcoders@yahoogroups.com, Rodrigo Pereira Fraga rpffoz@ wrote: Someone has some solution to use the Pattern OpenSessionInView with Flex using BlazeDS? I am using Spring and it contains a OpenSessionInViewFilter used in web.xml, and a OpenSessionInViewInterceptor. But it is different with Flex +) Someone has idea of how I can use the Lazy = true to hibernate with the Flex + Spring? Atenciosamente: --- | Rodrigo Pereira Fraga | http://www.digows.com e-mails: rpffoz@ rfraga@ ---
RE: [flexcoders] Re: Flex + Spring + Hibernate - Lazy=true
We haven't released the source for blazeds yet but it is coming. It does not contain any AS source generation but I think that is easy to layer on and there are a bunch of decent implementations out there. There is better support for customizing the serialization process in blazeds (improved over 2.5.1). The beta for blazeds has some of this but we are adding even more between beta and the release. Implementing lazy loading is a bit of a pain with hibernate if you have to do it using remote object. There are two major issues: 1) the class names of the generated wrapper classes used by hibernate mess up the mapping of the class names used to find the right AS class. This one is easy to get around with this PropertyProxy mechanism. In fact, LC DS contains the source to a PropertyProxy implementation (HibernatePropertyProxy.java) which you can use with remote object to strip the generated class name off before serialization. This has the side effect of returning empty versions of all non-loaded lazy properties which brings us to problem 2). Note that hibernate has different mechanisms for doing the lazy loading.. it can do byte code modification but I haven't used that technique so I'm not sure how it works here. 2) If you did not fetch a property with lazy=true in hibernate before the session is closed, the attempt to access that property during serialization fails with the session closed error. To get around this, you can make sure you access all properties you need before the serialization.. this is the approach used by LC DS but because it has a model of the association properties, you don't have to code it up yourself. It is done by the assembler so it is automatic.Another hacky approach is to put a servlet filter in which opens up a hibernate session before calling the MessageBrokerServlet, then close the session once it returns. That means you lose control over the hibernate sessions in your application and you have a transaction which is open for the entire duration of the request which is not very flexible. There might also be performance problems if you have a session/transaction open while you are doing I/O. Not sure that will be a problem but these are the reasons we went with the prefetch mechanism in LC DS's hibernate assembler. In terms of the issues with hibernate in 2.5 and earlier versions, one of the trickiest things is that you need to make your data-management-config.xml match up with the hibernate config. We're hoping to get a chance into a future version which makes this not necessary since the configs are pretty similar. You also need to do the AS code which matches the Java code yourself (or use a 3rd party code gen tool). Jeff From: flexcoders@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of andrii_olefirenko Sent: Friday, January 11, 2008 5:46 PM To: flexcoders@yahoogroups.com Subject: [flexcoders] Re: Flex + Spring + Hibernate - Lazy=true Assemblers are more for CRUD apps. And even with Hibernate assembler, i haven't achieved lazy loading (it was old version of FDS and maybe i didn't try hard but anyway). If anyone has been able to implement lazy loading with LCDS 2.5, let me know so at least i will be assured that this is possible :) in addition to lazy loading, there are also problems of multiple instances if the same object, and the need to manually write actionscript counterparts of java objects. IFAIK, there no tool for automated generation AS3 classes out of java classes in BlazeDS. For big projects with permanent changes to the objects it is pain to manually maintain both AS3 and java obejcts sync. it would be nice to implement all these features in open-sourced BlazeDS, but i didn't find any source code in distribution as for now. --- In flexcoders@yahoogroups.com mailto:flexcoders%40yahoogroups.com , Rodrigo Pereira Fraga [EMAIL PROTECTED] wrote: Oh my god =/ But who uses the LCDS, it does not contain a HibernateAssembler which implements the use of lazy? --- In flexcoders@yahoogroups.com mailto:flexcoders%40yahoogroups.com , andrii_olefirenko andriyo@ wrote: BlazeDS (and LCDS as far as i remember) doesn't support this out of box. There are workarounds like 1) make you own DTO (hibernate free) 2) prefetch object dependencies 3) include metadata about lazy properties with you objects, control externalization to handle objects with metadata and so on. if you develop with Hibernate (or EJB3), lack of lazy object support makes BlazeDS simply unusable for real enterprise application devs. --- In flexcoders@yahoogroups.com mailto:flexcoders%40yahoogroups.com , Rodrigo Pereira Fraga rpffoz@ wrote: Someone has some solution to use the Pattern OpenSessionInView with Flex using BlazeDS? I am using Spring and it contains a OpenSessionInViewFilter used in web.xml
