I have two content types: Region and City, Region
node includes City
node, every City
node is related to some Region
node, how I can create relationship for this situation: when I create Region
node and refer a City
node in a field, all City
nodes have its Region
referencing field set to this Region
node and vice-versa?
You can use Corresponding Entity References to achieve this.
Follow this steps:
Cities
in Region and Region
in City.