Re: [eclipselink-users] Mapping Question

[christopher delahunt <christopher.delahunt@xxxxxxxxxx>]

Hello,

Collection mappings (OneToMany and ManyToMany) are lazy loaded by 
default, so adding the FetchType.LAZY to them won't change anything 
unless they were explicitly eager before.  The fact that it is 
terminating without an error is troubling, as Java should throw or log 
an exception somewhere.  I doubt though that it is connections - any 
number of reads for a single tree will use the same connection, so it 
could be an OutOfMemory or other JVM error. 

Other than increasing the memory and the heap, you can make some of the 
backward relationships also lazy - specifically the ManyToOne back 
pointers.  This will prevent the entire tree from being inadvertently 
brought into memory when not needed.  You can also look at where a 
relationship is not strictly needed and unmap them - bringing them in 
using a query instead when they are needed.  For instance, in a 
ManyToMany, it may not be necessary to have both sides mapped if the 
application will only ever us it from one side. 

Best Regards,
Chris

Roger wrote:
> Hi
>
> I have a series of entities representing a hierarchy. Entity1 has many Entity2 
> which in turn has many Entity3 which in turn ... etc, etc.
>
> Entity1 maps Entity2 with a @OneToMany and Entity2 maps to Entity1 with 
> @ManyToOne and Fetch=FetchType.Lazy. This is repeated down the heirarchy.
>
> So far, this has been working well since I'm usually starting at the top of 
> the hierarchy until this afternoon when I was lumbered with one of those 
> urgent, need it yesterday type of jobs. What I needed to do was to read 
> through the entities that live at the bottom level of the hierarchy.  For each 
> entity, EclipseLink walked up  the hierarchy (running with debug level 
> logging) and terminated midway through the query with
> no obvious error messages, so whether it ran out of DB Connections or memory I 
> don't know. I tried adding fetch = FetchType.LAZY to the @OneToMany mappings 
> with no effect.
>
> Is there anything I can do to stop EclipseLInk doing this and only walking 
> back up the hierarchy when I try to access the level above. In this particular 
> instance all the data I need is in the bottom level entity,
>
> Regards
>
>  
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