QGIS 3 - Python : QgsVectorLayerJoinInfo issue

Question

I'm trying to use Python to join a table to a vector layer within QGIS (v. 3.2.0)

Here is the script I use :

>>>root = QgsProject.instance().layerTreeRoot()
>>>ids = root.findLayerIds()
>>>target=QgsProject.instance().mapLayer(ids[1])
>>>print ("target :",target.id())
target : du_fl_pts_e154c28b_4812_41a2_9a78_bf95b7a97926
>>>layerToJoin=QgsProject.instance().mapLayer(ids[0])
>>>print("Layer to join :",layerToJoin.id())
Layer to join : TAXREF_9ab461d0_81d1_4095_b1d0_dce90b20600e
>>>lien = QgsVectorLayerJoinInfo()
>>>lien.targetFieldName = 'CD_REF'
>>>lien.joinLayerId = ids[0]
>>>lien.joinFieldName = 'CD_NOM'
>>>target.addJoin(lien)
True

But after the execution of this script, I have no join on my target layer.

Interesting fact : when I test the same script on the same layers/tables on QGIS 2.18.21 (just changing QgsProject -> QgsMapLayerRegistry and QgsVectorLayerJoinInfo -> QgsVectorJoinInfo) the join works.

Any idea why this doesn't work on QGIS 3?

Answer 1

You need to rename some of your functions as described in the API for the new QgsVectorLayerJoinInfo class in QGIS 3.

E.g.

• targetFieldName() should now be setTargetFieldName()
• joinLayerId() should now be setJoinLayerId()

etc.

---

So try using something like the following:

lien = QgsVectorLayerJoinInfo()
lien.setJoinFieldName('CD_NOM')
lien.setTargetFieldName('CD_REF')
lien.setJoinLayerId(layerToJoin.id())
lien.setUsingMemoryCache(True)
lien.setJoinLayer(layerToJoin)
target.addJoin(lien)