Thanks to you and for the ongoing work! 2016-10-20 8:14 GMT+02:00 Matthias Kuhn <[email protected]>:
> On 10/20/2016 12:33 AM, Nyall Dawson wrote: > > On 19 October 2016 at 22:22, Neumann, Andreas <[email protected]> > wrote: > > - attributes from the parent feature are automatically available > > within the filter, UNLESS there's a duplicate field name from the > > child feature > > I like this, e.g. PostgreSQL handles it the same way for joined fields. > But it warns in case of duplication and requires an explicit source > table statement in case of duplication. In the case where the child > feature suddenly gets a new field with the same name, the semantic of > the expression should not silently change but a warning be issued. > > > - expose the parent feature via the variable @parent. This could be > > used with the functions geometry(@parent), attribute(@parent, > > "some_dup_field_name") > > Based on above statement, there should also be a @child variable. > Or attributes could be exposed as parent.attr / child.attr. > > > > > Then you'd be able to write: > > > > aggregate ('mypoint', 'count', "id", intersects ($geometry, > geometry(@parent))) > > aggregate('mypoint', 'count', "id", mypoint.fk = @parent.id)) > > or > > aggregate('mypoint', 'count', "id", attribute(@child, "id") = > attribute(@parent, "id")) > > # Error in case both have a field "id" > aggregate('mypoint', 'count', "id", mypoint.fk = "id")) > > > > > The trickiest part in implementing this would be making sure the > > current aggregate value cache correctly handles use of parent feature > > attributes/geometry. > > > > Re virtual layers: I've always seen these as a "heavier" (+ more > > powerful!) approach, which is OK for some use cases but for others (Eg > > data defined controls, composer labels, etc) it's preferable to have > > these calculations available directly within the expression engine. > > I also think this needs to be fixed in expressions. I have a use-case > for it with default values at the moment. > > Matthias > _______________________________________________ > Qgis-user mailing list > [email protected] > List info: http://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user >
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