flexible QVariantMap creatOptions parameters which include an
optional fileEncoding value
More flexible, allows sinks to be created using any creation
option which is passed to the underlying provider
Instead, parameters evaluate to QgsFeatureSource, which are
used for retrieving features, feature count, crs, wkb type,
etc.
This abstracts away the actual feature source, so that
algorithms may potentially operate from non-layer
feature sources.
It also helps remove the need for specialised QgsProcessingUtils
methods like getFeatures, featureCount, and createSpatialIndex.
Instead the standard API methods using QgsFeatureSources can
be used instead.
This implements an improved version of vector.createVectorWriter
in QgsProcessingUtils. The improved version relies on the
core class QgsVectorLayerImport to create empty layers,
which:
- reduces duplicate code and reuses the mature QgsVectorLayerImport
routines
- avoids manual conversion of field types to destination provider
field types
- potentially allows any writable provider to be used as a feature
sink for algorithms (e.g. output direct to MSSQL/Oracle/db2). This
should work now - it just needs exposing via UI.
Algorithms and other processing code should use this method
(instead of dataobjects.getLayerFromString) to
retrieve layers from a string, as it considers the processing
context and allows resolving strings to temporarily stored layers.
This permits processing models to function correctly when
intermediate results are stored as memory layers. Subsequent
model algorithms can then access these temporary layers as inputs.
All temporary layers will be removed when the context object
is destroyed after the model algorithm is run.
Remove processing vector.uniqueValues/vector.getUniqueValues
and port usage to c++ method
Should be much faster than the python method, as the c++ method takes
advantage of handing off the unique values calculation to the
provider source whenever possible
Also
- simplify and add tests
- remove large memory leak (persistant store of all non-project layers)
- remove broken support for direct loading postgres/virtual layers
by string (Python version was very broken and would never match
a postgres/virtual layer)
