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Re: [eclipselink-users] Specify MaxResultSize of "owning" Entity with @QueryHint(LEFT_FETCH...) in NamedQuery + .setMaxResults() ???
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Hello Mario,
Joining and batch reading on collection types do not work well when
using cursors or other features that limit the results returned. These
features work on the database results, not the returned objects to avoid
having to bring in large amounts of data. Unfortunately, there is no
way to limit database results to a set number of objects on an object
bases. There is no way to know without reading in all the rows to tell
when a particular object is done being built.
If the reason for limiting results is to limit memory use, I would
suggest that you not using joining,and instead allow EclipseLink to read
in Addresses and Roles with individual queries as it builds each
partner. If you are using the cache, some of the partner objects may
already exist there, so these queries might not always be necessary.
Best Regards,
Chris
Mario Sandro Schwarz wrote:
Hello everybody,
I have a Partner entity which can have multiple Addresses and multiple
Roles.
I have a use-case-based query which should retrieve always 50 partners
in paging mode.
So I created a NamedQuery, which Selects all Partners and uses two
LEFT_FETCH QueryHints to obtain the Adresses and the roles to the
partners and limits the result by .setMaxResults. The problem is that
the number of results specified by .setMaxResults() refers the whole
result set and not just the owning partner entities. And that result
set dramatically varies.
Assuming I have 50 Partners, each Partner has 10 addresses and 10
roles. In that case I´d have to set .setMaxResults() to 5000.
But what if just the half of the 50 partners have 10 addresses and 10
roles, let´s say the other 25 just have 3.
That would be 25 * 10 * 10 + 25 * 3 * 3 = 2725 rows in the result set.
Any help is appreciated!
Mario
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