Removing table join using PyQGIS

attribute-joinspyqgisremovevector

I joined a table to a layer in QGIS using code from this thread: Joining layers with PyQGIS 3.
Now I would like to remove the join. How can I do it?

Best Answer

QgsVectorLayer possesses a method for that: removeJoin(joinLayerId: str).

So, if layer2 was initially joined to layer1, the code for removing the join may look like this:

from qgis.core import QgsProject

layer1 = QgsProject.instance().mapLayersByName("LAYER 1")[0]
layer2 = QgsProject.instance().mapLayersByName("LAYER 2")[0]

ids_of_joins_in_layer1 = [join.joinLayerId() for join in layer1.vectorJoins()]

if layer2.id() in ids_of_joins_in_layer1:
    layer1.removeJoin(layer2.id())

Related Solutions

[GIS] How to remove a join (between a standalone table and a feature layer) with ArcObjects

Code below works for me for a featurelayer. Similar logic could be used for a standalone table.

private void RemoveAllJoins(IFeatureLayer fLayer)
{
    var dispTable = fLayer as IDisplayTable;
    var rqt = dispTable.DisplayTable as IRelQueryTable;
    if (rqt != null)
    {
        Debug.Print("source: {0}", ((IDataset)rqt.DestinationTable).Name);
        Debug.Print("dest: {0}", ((IDataset)rqt.SourceTable).Name);
        fLayer.FeatureClass = (IFeatureClass)rqt.DestinationTable;
    }
    else
        Debug.Print("there are no joins");
}

The documentation for IRelQueryTable at 10 seems to be missing this important graphic, that appears in 8.3 help doc:

enter image description here

[GIS] Joining table field with shapefile using PyQGIS

This has worked for me:

# Get input (csv) and target (Shapefile) layers
shp=iface.activeLayer()
csv=iface.mapCanvas().layers()[0]

# Set properties for the join
shpField='code'
csvField='codigo'
joinObject = QgsVectorJoinInfo()
joinObject.joinLayerId = csv.id()
joinObject.joinFieldName = csvField
joinObject.targetFieldName = shpField
shp.addJoin(joinObject)

The error you are facing is, believe it or not, by a typo in joinLayerId. The question is, why QGIS doesn't throw an error there?

Best Answer

Related Solutions

[GIS] How to remove a join (between a standalone table and a feature layer) with ArcObjects

[GIS] Joining table field with shapefile using PyQGIS

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