[Qgis-developer] Python and strange results using layer(.dataProvider()).getFeatures(...)

[Casper Børgesen (CABO)]

Hi Nathan

Thanks for clarifying that, I’ll try to put my faith in the layer. My question is then, why does the layer only respond with 2 features when I ask it for max 3 features, since 4 – 1 = 3?

Does it find 3 features, determine that one of them has been deleted and only returns the two living features?`
Regards, Casper

From: Nathan Woodrow [mailto:madmanwoo at gmail.com]
Sent: 30. august 2016 14:50
To: Casper Børgesen (CABO)
Cc: QGIS Developer Mailing List
Subject: Re: [Qgis-developer] Python and strange results using layer(.dataProvider()).getFeatures(...)

If you haven't saved the layer after you did the delete the provider still thinks there is 4 features. The layer itself and the edit buffer sit above the data provider.

Generally you should trust the layer as it knows the state of the edit buffer.

On Tue, Aug 30, 2016 at 10:32 PM, Casper Børgesen (CABO) <CABO at niras.dk<mailto:CABO at niras.dk>> wrote:
Hi,

I have a point SHAPE layer with 4 points on a line (just to make them easy to number in this example, and the layer is created in QGIS).


1.       Start editing.

2.       Delete point number 3.

3.       In the python console do the following:

>>> len(list(iface.mapCanvas().currentLayer().getFeatures()))
3
>>> len(list(iface.mapCanvas().currentLayer().dataProvider().getFeatures()))
4
>>> req = QgsFeatureRequest()
>>> req = req.setLimit(3)
>>> len(list(iface.mapCanvas().currentLayer().getFeatures(req)))
2
>>> len(list(iface.mapCanvas().currentLayer().dataProvider().getFeatures(req)))
3

If I access the features using the data provider with no request, I get too many features back. If I use a request when getting features directly from the layer, I get too few features back.

I guess the layer directly gives me the best result, but it chokes when the request is limited.

Who can I trust when getting features during an editing session? Or should I approach this in another way?

Regards, Casper

Using QGIS master (d3882d5) in Windows 7, x64

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