Save as output layer from QGIS processing algorithm to PostGIS database using PyQGIS

Question

I have two layers(layer1,layer2) in PostGIS database where I have connect in QGIS project.

My database have specific precision. Now I want to use from QGIS processing some algorithms like GISDIFFERENCE(for example I know tew postgis have query for this). But I don't know how to import the algorithm output in PostGIS database automatic to keep my database precision.

For example, if I try to run graphical this tool show me choose to save as to PostGIS database. Because I want to create a QGIS plugin.

Some way is to run algorithms and I save manual the output to shapefile and after to import this shapefile to PostGIS database like this :

outputs_QGISDIFFERENCE_1=processing.runalg('qgis:difference', layer1,layer2,False,None)
load= QgsVectorLayer(outputs_QGISDIFFERENCE_1['OUTPUT'],'myname', 'ogr')
 QgsMapLayerRegistry.instance().addMapLayer(load)

and save to PostGIS database.

But that way create it me topology error because I loose the database precision if I use the graphical way to save as to PostGIS database then that layer is correct.

But how to do this using PyQGIS?

• Germán Carrillo: Still interested in this question?

Answer 1

Consider using something like this:

def updateOriginalLayer(self, pgInputLayer, qgisOutputVector):
 """
 Updates the original posts layer using the processing output layer
 pgInputLyr: postgis input layer
 qgisOutputVector: qgis processing output layer
 """
 provider = pgInputLayer.dataProvider()
 # getting keyColumn because we want to be generic
 uri = QgsDataSourceURI(pgInputLayer.dataProvider().dataSourceUri())
 keyColumn = uri.keyColumn()
 # starting edition mode
 pgInputLayer.startEditing()
 addList = []
 idsToRemove = []
 #making the changes and inserts
 for feature in pgInputLayer.getFeatures():
 id = feature.id()
 outFeats = []
 #getting the output features with the specific id
 if qgisOutputVector:
 for gf in qgisOutputVector.dataProvider().getFeatures(QgsFeatureRequest(QgsExpression("{0}={1}".format(keyColumn, id)))):
 outFeats.append(gf)
 #starting to make changes
 for i in range(len(outFeats)):
 if i == 0:
 #let's update this feature
 newGeom = outFeats[i].geometry()
 newGeom.convertToMultiType()
 feature.setGeometry(newGeom)
 pgInputLayer.updateFeature(feature)
 else:
 #for the rest, let's add them
 newFeat = QgsFeature(feature)
 newGeom = outFeats[i].geometry()
 newFeat.setGeometry(newGeom)
 idx = newFeat.fieldNameIndex(keyColumn)
 newFeat.setAttribute(idx, provider.defaultValue(idx))
 addList.append(newFeat)
 #in the case we don't find features in the output we should mark them to be removed
 if len(outFeats) == 0:
 idsToRemove.append(id)
 #pushing the changes into the edit buffer
 pgInputLayer.addFeatures(addList, True)
 #removing features from the layer
 pgInputLayer.deleteFeatures(idsToRemove)