Adds a new abstract base class QgsMetadataValidator for validating
metadata against standard schemas.
Initially only QgsNativeMetadataValidator for validating against
the native QGIS metadata schema is implemented.
In future this could be extended with Dublin Core, ISO 19115
validators, etc...
QgsLayerMetadata handles storage and management of the metadata
for a QgsMapLayer. This class is an internal QGIS format with a common
metadata structure, which allows for code to access the metadata properties for
layers in a uniform way.
The metadata store is designed to be compatible with the Dublin Core metadata
specifications, and will be expanded to allow compatibility with ISO specifications
in future releases. However, the QGIS internal schema does not represent a superset
of all existing metadata schemas and accordingly conversion from specific
metadata formats to QgsLayerMetadata may result in a loss of information.
This class is designed to follow the specifications detailed in
the schema definition available at resources/qgis-resource-metadata.xsd
within the QGIS source code.
A simple feature sink which proxies feature addition on to another feature sink.
This class is designed to allow factory methods which always return new QgsFeatureSink
objects. Since it is not always possible to create an entirely new QgsFeatureSink
(e.g. if the feature sink is a layer or a layer's data provider), a new
QgsProxyFeatureSink can instead be returned which forwards features on to
the destination sink. The proxy sink can be safely deleted without affecting
the destination sink.
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.
