[QGIS-Developer] attribute join questions

[Alexis R.L.]

Greeting everyone,

I had an idea and wanted to see i it was good or not.

I have been thinking about ways to improve our joining algs. This proposal
mostly apply to the attribute table join. I want to improve the spatial
join too to reach speed similar to esri's but I'm not sure how they do it.

I thought that we could possibly speed up and provide more flexibility by
using hashes, this way we could also multi-attribute join ( as it was
recently implemented for the table join).

The idea would be to get the desired field (or fields) in the selected
order. Make a QHash< QVarList, QFeatureIds>. This would require to go
through both features once for mapping and another time for
extraction/joining. We could also cache the full list of selected
attributes instead of the featureids but this would take up more memory but
prevent the extraction step.

Is that a good idea or is it more wasteful/slow that the current
implementation?


Alex
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