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From Aristedes Maniatis <...@maniatis.org>
Subject Re: cayenne performance tuning issues
Date Wed, 18 Dec 2013 03:49:50 GMT
On 18/12/2013 4:29am, Michael Hatch wrote:

> The first sql statement is fetching the user info, while the second sql is
> for inflating the roles relationship. I understand the documentation
> explicitly states that prefetching will inflate relationships for you, but
> it still does so via multiple sql commands per relationship, instead of via
> a single sql statement with an inner join. Did I simply do something wrong
> somewhere?

Cayenne will automatically decide whether to issue multiple SQL requests (disjoint prefetch)
or one big SQL statement which captures all the data (joint). Don't assume without testing
which one will be better for your needs, and Cayenne does allow you to choose which sementics
to use. But SelectQuery will be disjoint by default.

Imagine for a moment: to-many joins to 5 tables from a source table on which you want to use
a joint prefetch. You can very quickly return a vast number of rows using an outer join in
this way.

Ari


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Aristedes Maniatis
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