action.py

'''
QGIS Action to select and zoom the feature from related table 
when one of field pairs is string. Using LIKE in QgsExpression.

Ref: https://lists.osgeo.org/pipermail/qgis-it-user/2017-April/002413.html
'''

from qgis.utils import iface

# inserire qui il nome del layer geometrico
vl = QgsMapLayerRegistry.instance().mapLayersByName('punti')[0]
iface.setActiveLayer(vl)
cLayer = iface.mapCanvas().currentLayer()

# qui sotto i nomi dei due campi da correlare
expr = QgsExpression("id_punto LIKE '[% "punto" %]%'")
it = cLayer.getFeatures( QgsFeatureRequest( expr ) )
ids = [i.id() for i in it]
cLayer.setSelectedFeatures( ids )

# zoom alla selezione
box = cLayer.boundingBoxOfSelected()
iface.mapCanvas().setExtent(box)
iface.mapCanvas().refresh()