Chain two processes with in-memory layer in QGIS

Question

I have two processes which should run after each other, first dissolve, then multipart-singlepart. Until now I have worked with file-based layers but I would like to have the output from the dissolve process as an in-memory layer which should be used in the multipart-to-singlepart process.

Currently I have each process in a single script, but would like to have them integrated into one.

This is my code so far:

Script 'Dissolve'

from qgis.core import *
import os
import processing
pathInput = "path/to/input.shp"
pathOutput = "path/to/dissolved.shp"
# Dissolve features based on values in attribute table field
processing.run("native:dissolve",{'INPUT':pathInput, 
 'FIELD':['highway', 'maxspeed', 'surface'],
 'OUTPUT':pathOutput}

Script 'Multipart to singlepart'

pathInput = "path/to/dissolved.shp"
pathOutput = "path/to/singlepart.shp"
processing.run("qgis:multiparttosingleparts",{'INPUT':pathInput, 
 'OUTPUT':pathOutput}
 )

How can I run this without creating an actual dissolve.shp-file, but instead create and use an in-memory layer, so that I can integrate both processes into one script? I'm very sorry if this seems to be an easy task, however, I couldn't find the proper information on how to 'chain' those processes with temporary files, especially, because I don't know how to refer to the temporary dissolve file to use it in the next process.

System Windows 10

QGIS 3.28 Firenze

• i.i.k.: I think I may found an answer, referring to this source : gis.stackexchange.com/questions/284064/…. So I may need to add dissolve_result = processing.run("native:dissolve",{'INPUT':pathInput, 'FIELD':['highway', 'maxspeed', 'surface'], 'OUTPUT':'memory:'} and then I'll be able to refer to the output by dissolve_layer = dissolve_result['OUTPUT']
• Kalak: Yes that's how it is done
• Bera: anitagraser.com/…

Answer 1

The solution to chain two processes and using in-memory layer is by assigning a name to the process and defining the output of the process as 'memory:'. In my case, the code for chaining the two process is:

from qgis.core import *
import os
import processing
pathInput = "path/to/input/file.shp"
pathOutput= "path/to/output/file.shp"
# Dissolve features based on values in an attribute table field
dissolve = processing.run("native:dissolve",{'INPUT':pathInput, 
 'FIELD':['highway', 'maxspeed', 'surface'],
 'OUTPUT':'memory:'})
 
dissolve_layer = dissolve['OUTPUT']
# Apply multipart-to-singleparts on memory-layer and save result as file
processing.run("qgis:multiparttosingleparts",{'INPUT':dissolve_layer, 
 'OUTPUT':pathOutput}
 )