[FEATURE][processing] New input type for expressions #3713
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IMVHO: great idea, thanks. |
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I like the idea. Also in future it would be nice to have ability include in expressions numeric outputs from other algorithms and accept strings with formulas. |
This was referenced Nov 9, 2016
accept numeric, file and table field inputs in modeler This allows a non-string parameter to be reused as a string parameter in contexts where it makes sense.
This adds a new input type for expression inputs. Expression inputs can be linked to a parent layer so that the builder shows the correct fields and layer variables. It's designed for two use cases: 1. to be used when an algorithm specifically requires an expression, eg Select by Expression and Extract by Expression. 2. to be potentially used as a replacement input instead of string or number literals in algorithms. Eg - if the simplify algorithm tolerance parameter was replaced with an expression paremeter, then this expression would be evaluated for every feature before simplifying that feature. It would allow parameters to be calculated per feature, as opposed to the current approach of calculating a parameter once before running the algorithm. It would also mean algorithms like "variable distance buffer" would no longer be needed, as a single "buffer" algorithm could then be used for either a fixed distance, field based, or expression based distance.
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This adds a new input type for expression inputs. Expression inputs can be linked to a parent layer so that the builder shows the correct fields and layer variables.
It's designed for two use cases:
to be used when an algorithm specifically requires users to enter an expression as an input, eg Select by Expression and Extract by Expression. In this case it has the benefit of showing the expression builder and linking it correctly with the parent layer.
to be potentially used as a replacement input instead of string or number literals in algorithms. Eg - if the simplify algorithm tolerance parameter was replaced with an expression parameter, then this expression would be evaluated for every feature before simplifying that feature. It would allow parameters to be calculated per feature, as opposed to the current approach of calculating
a parameter once before running the algorithm. It would also mean algorithms like "variable distance buffer" would no longer be needed, as a single "buffer" algorithm could then be used for either a fixed distance, field based, or expression based distance.
This is just a concept for now - if the processing team like this idea then i'll add unit tests + proper expression context handling, and update existing algorithms to suit.