Creating custom categorized symbology and coloring based on two fieldNames

Question

I am developing a plugin in PyQGIS 3. Within this plugin, I want to change the symbology of a layer to categorized. I want to categorize based on the column Collecti_2 in PyQGIS 3. This step has been done in the first section of the code. However, when I want to give these produced categories a color based on the fieldName Color the results are colored shapefiles with a legend that contains only blue colors? This is my code:

#add National_BC_produced
layer = QgsVectorLayer(output_folder + 'National_BC_Joined3_' + str(year) + '.shp', "Collection_Systems_" + str(year), "ogr")
QgsProject.instance().addMapLayer(layer)
layer = QgsProject().instance().mapLayersByName('Collection_Systems_' +str(year))[0]

fieldName = 'Collecti_2'
fieldIndex = layer.fields().indexFromName(fieldName)
categories = []

for u in layer.uniqueValues(fieldIndex):
    symbol = QgsSymbol.defaultSymbol(layer.geometryType())
    category = QgsRendererCategory(u, symbol, str(u))
    categories.append(category)
    
renderer = QgsCategorizedSymbolRenderer(fieldName, categories)
style = QgsStyle().defaultStyle()

# The "magic" missing part
for index, category in enumerate(renderer.categories()):
    newSymbol = QgsFillSymbol()
    newSymbolLayer = newSymbol.symbolLayers()[0]
    data_defined = QgsProperty.fromField("Color")  # "color" is the name of the field
    newSymbolLayer.setDataDefinedProperty(QgsSymbolLayer.PropertyFillColor, data_defined)  
    newSymbol.appendSymbolLayer(newSymbolLayer)
    renderer.updateCategorySymbol(index, newSymbol)

layer.setRenderer(renderer)
layer.triggerRepaint()

And these are the results:

How can I create a code which also gives the categories in the legend a same color?

Answer 1

I have no idea what the problem is. It may be related to setDataDefinedProperty. Instead, I made a dictionary containing {"Type": "Color"} and used setFillColor.

Use this script:

layer = ....

fieldName = 'Collecti_2'
fieldIndex = layer.fields().indexFromName(fieldName)

uvp_set = set([(f["Collecti_2"], f["Color"]) for f in layer.getFeatures()])
uvp_dict = {i[0]: i[1] for i in uvp_set}

categories = {}
for u in uvp_dict:
    symbol = QgsSymbol.defaultSymbol(layer.geometryType())
    category = QgsRendererCategory(u, symbol, str(u))
    categories[u] = category

renderer = QgsCategorizedSymbolRenderer(fieldName, categories.values())
style = QgsStyle().defaultStyle()

for index, [code, category] in enumerate(categories.items()):
    newSymbol = QgsFillSymbol()
    newSymbolLayer = newSymbol.symbolLayers()[0]
    newSymbolLayer.setFillColor(QColor(uvp_dict[code]))
    newSymbol.appendSymbolLayer(newSymbolLayer)
    renderer.updateCategorySymbol(index, newSymbol)

layer.setRenderer(renderer)
layer.triggerRepaint()