add associateJoin function #157
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this helps avoid N+1 queries
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It looks like the lower bound on |
parsonsmatt
requested changes
Oct 24, 2019
| -- 'where_' (foo '^.' FooParentId '==.' 'val' parentId) | ||
| -- 'pure' (foo, bar) | ||
| -- @ | ||
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| -- getFoosAndNestedBarsFromParent :: ParentId -> (Map (Key Foo) (Foo, [Entity Bar])) | ||
| -- getFoosAndNestedBarsFromParent parentId = 'fmap' associateJoin $ 'select' $ | ||
| -- 'from' $ \\(foo `'LeftOuterJoin`` bar) -> do | ||
| -- 'on' (bar '^.' BarFooId '==.' foo '^.' FooId) |
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The bar access here should use ?. because a LeftOuterJoin implies nullability on the right hand side. That this isn't enforced is a bug (see #150). The type of this would then be Map (Key Foo) (Foo, [Maybe (Entity Bar)]).
| Map.insertWith | ||
| (\(oneOld, manyOld) (_, manyNew) -> (oneOld, manyNew ++ manyOld )) | ||
| (entityKey one) | ||
| (entityVal one, [many]) |
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I think I'd define this directly in Database.Esqueleto and not one of the internal modules. It's easy to miss the reexports necessary.
- moves associateJoin to Database.Esqueleto - relaxes bounds on containers dep -
parsonsmatt
approved these changes
Oct 25, 2019
| ======== | ||
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| - @tippenein | ||
| - [#149](https://github.com/bitemyapp/esqueleto/pull/157): Added `associateJoin` query helpers. |
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This function might want to live in esqueleto for avoiding N+1 queries? Just a rough example here along with (probably insufficient) code comment. It also adds a
containersdep which might be undesirable.