Port merge lines algorithm to new API

Author: nyalldawson

python/plugins/processing/algs/qgis/MergeLines.py

@@ -27,23 +27,18 @@
 
 import os
 
-from qgis.core import QgsFeature, QgsFeatureSink, QgsProcessingUtils
+from qgis.core import (QgsProcessing,
+                       QgsWkbTypes)
 
 from qgis.PyQt.QtGui import QIcon
 
-from processing.algs.qgis.QgisAlgorithm import QgisAlgorithm
-from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
-from processing.core.parameters import ParameterVector
-from processing.core.outputs import OutputVector
-from processing.tools import dataobjects
+from processing.algs.qgis.QgisAlgorithm import QgisFeatureBasedAlgorithm
 
-pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
 
+pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
 
-class MergeLines(QgisAlgorithm):
 
-    INPUT_LAYER = 'INPUT_LAYER'
-    OUTPUT_LAYER = 'OUTPUT_LAYER'
+class MergeLines(QgisFeatureBasedAlgorithm):
 
     def icon(self):
         return QIcon(os.path.join(pluginPath, 'images', 'ftools', 'to_lines.png'))
@@ -57,41 +52,27 @@ def group(self):
     def __init__(self):
         super().__init__()
 
-    def initAlgorithm(self, config=None):
-        self.addParameter(ParameterVector(self.INPUT_LAYER,
-                                          self.tr('Input layer'), [dataobjects.TYPE_VECTOR_LINE]))
-        self.addOutput(OutputVector(self.OUTPUT_LAYER, self.tr('Merged'), datatype=[dataobjects.TYPE_VECTOR_LINE]))
-
     def name(self):
         return 'mergelines'
 
     def displayName(self):
         return self.tr('Merge lines')
 
-    def processAlgorithm(self, parameters, context, feedback):
-        layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
-
-        writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), layer.wkbType(), layer.crs(), context)
-
-        features = QgsProcessingUtils.getFeatures(layer, context)
-        total = 100.0 / layer.featureCount() if layer.featureCount() else 0
-
-        for current, inFeat in enumerate(features):
-            outFeat = QgsFeature()
-            attrs = inFeat.attributes()
-            outFeat.setAttributes(attrs)
+    def outputName(self):
+        return self.tr('Merged')
 
-            inGeom = inFeat.geometry()
-            if inGeom:
-                outGeom = inGeom.mergeLines()
-                if outGeom is None:
-                    raise GeoAlgorithmExecutionException(
-                        self.tr('Error merging lines'))
+    def outputType(self):
+        return QgsProcessing.TypeVectorLine
 
-                outFeat.setGeometry(outGeom)
+    def outputWkbType(self, input_wkb):
+        return QgsWkbTypes.MultiLineString
 
-            writer.addFeature(outFeat, QgsFeatureSink.FastInsert)
-            feedback.setProgress(int(current * total))
+    def processFeature(self, feature, feedback):
+        input_geometry = feature.geometry()
+        if input_geometry:
+            output_geometry = input_geometry.mergeLines()
+            if not output_geometry:
+                feedback.reportError(self.tr('Error merging lines for feature {}').format(feature.id()))
 
-        del writer
+            feature.setGeometry(output_geometry)
+        return feature

python/plugins/processing/algs/qgis/QGISAlgorithmProvider.py

@@ -73,6 +73,7 @@
 from .LinesToPolygons import LinesToPolygons
 from .MeanCoords import MeanCoords
 from .Merge import Merge
+from .MergeLines import MergeLines
 from .NearestNeighbourAnalysis import NearestNeighbourAnalysis
 from .OffsetLine import OffsetLine
 from .Orthogonalize import Orthogonalize
@@ -158,7 +159,6 @@
 # from .DefineProjection import DefineProjection
 # from .RectanglesOvalsDiamondsVariable import RectanglesOvalsDiamondsVariable
 # from .RectanglesOvalsDiamondsFixed import RectanglesOvalsDiamondsFixed
-# from .MergeLines import MergeLines
 # from .PointsAlongGeometry import PointsAlongGeometry
 # from .Relief import Relief
 # from .IdwInterpolation import IdwInterpolation
@@ -213,7 +213,7 @@ def getAlgs(self):
         #         OrientedMinimumBoundingBox(),
         #         SpatialIndex(), DefineProjection(),
         #         RectanglesOvalsDiamondsVariable(),
-        #         RectanglesOvalsDiamondsFixed(), MergeLines(),
+        #         RectanglesOvalsDiamondsFixed(),
         #         PointsAlongGeometry(),
         #         Relief(),
         #         IdwInterpolation(), TinInterpolation(),
@@ -258,6 +258,7 @@ def getAlgs(self):
                 LinesToPolygons(),
                 MeanCoords(),
                 Merge(),
+                MergeLines(),
                 NearestNeighbourAnalysis(),
                 OffsetLine(),
                 Orthogonalize(),

python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml

@@ -389,18 +389,18 @@ tests:
 #        compare:
 #          geometry:
 #            precision: 7
-#
-#  - algorithm: qgis:mergelines
-#    name: Merge lines algorithm
-#    params:
-#      INPUT_LAYER:
-#        name: multilines.gml
-#        type: vector
-#    results:
-#      OUTPUT_LAYER:
-#        name: expected/merge_lines.gml
-#        type: vector
-#
+
+  - algorithm: qgis:mergelines
+    name: Merge lines algorithm
+    params:
+      INPUT:
+        name: multilines.gml
+        type: vector
+    results:
+      OUTPUT:
+        name: expected/merge_lines.gml
+        type: vector
+
   - algorithm: native:multiparttosingleparts
     name: Multiparts to singleparts
     params: