How to set and configure a value relation edittype in QGIS 2.14?

Question

I am trying to set the edit type of a vector layer to use a value relation, by pyqgis. So my question is exactly the same as this, except now it is qgis 2.14. I found that setEditForm is deprecated and this method is recommended instead:

vlayer.editFormConfig().setWidgetType(index,"ValueRelation")

setWidgetType sets the edit widget correctly but then I have the same problems as in the question regarding qgis 2.0. I.e. python commands are processed without errors or warnings but the when I check the properties in QGIS, the widget settings are empty:

vlayer.valueRelation(index).mLayer = target_layer.id()
vlayer.valueRelation(index).mKey = key_field
vlayer.valueRelation(index).mValue = value_field
vlayer.valueRelation(index).mAllowNull = True
vlayer.valueRelation(index).mOrderByValue = True

How do I define the value relation by pyqgis in qgis 2.14?

Answer 1

The options for the widget configurations are passed in as dict.

It's best to inspect first what a manually configured (and working) configuration looks like.

vlayer.editFormConfig().widgetConfig(index)

With this command you will see, that a ValueRelation accepts the following configuration options:

• FilterExpression
• Layer
• UseCompleter
• AllowMulti
• AllowNull
• OrderByValue
• Value
• Key

Now simply do it the other way round:

cfg = dict()
cfg['Layer'] = target_layer.id()
cfg['Key'] = key_field
cfg['Value'] = value_field
cfg['AllowNull'] = True
cfg['OrderByValue'] = True
# Add more if you like
vlayer.editFormConfig().setWidgetConfig(index, cfg)