[Qgis-developer] QgsDataProvider and supportsSubsetString

Chris Crook ccrook at linz.govt.nz
Tue Apr 30 11:13:41 PDT 2013


Thanks for pointer, I hadn't seen that, and certainly it is a similar thing in terms of implementation (ie when the filter is applied as features are extracted).

There would still be the question of where and how the request is presented to the user (ie what sort of request is available, though of course an expression based filter is always an option), and how it is defined with the layer and persisted into the project.   Also the subset has its own feature count and extents, so that may not sit will with a feature request implementation. 

From: Nathan Woodrow [madmanwoo at gmail.com]
Sent: 30 April 2013 18:55
To: Chris Crook
Cc: qgis-developer at lists.osgeo.org
Subject: Re: [Qgis-developer] QgsDataProvider and supportsSubsetString


Also not there is previsions to add this kind of thing to QgsFeatureRequest http://www.qgis.org/api/qgsfeaturerequest_8h_source.html

- Nathan

On Tue, Apr 30, 2013 at 4:33 PM, Chris Crook <ccrook at linz.govt.nz<mailto:ccrook at linz.govt.nz>> wrote:
Hi All

As we are looking at API tidy ups (I understand), would there be any support for providing a bit more granularity in supportsSubsetString.  At the moment this is a simple boolean, and the GUI offers a SQL based subset string builder.

However not all providers naturally use SQL based strings.  I'm interested in adding subset capability to the delimited text provider, whichi I've done using QgsExpression as the basis for subsets.  This works very well except that the GUI isn't an expression builder.  I think there may be similar issues with the WFS provider.

What I am proposing is something more like an enum QgsDataProvider::SubsetStringType, which could then be interrogated by the properties dialog to select the appropriate query builder dialog.

Logically this would supplant the supportsSubsetString boolean which could be deprecated, replaced with

virtual QgsDataProvider::SubsetStringType QgsDataProvider::subsetStringType(){ return NoSubsetString; }

Other types could be SqlSubsetString, ExpressionSubsetString, ...?

Thoughts anyone?


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