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--- modul:m320_2024:learningunits:lu09:zweiseitige_mehrfachbeziehung [2024/09/23 09:12] – angelegt msuter
+++ modul:m320_2024:learningunits:lu09:zweiseitige_mehrfachbeziehung [2024/09/23 09:48] (aktuell) – [Umsetzung in Python] msuter
@@ Zeile 19: / Zeile 19: @@
 Nur wenn dies der Fall ist, wird die Beziehung hinzugefügt bzw. gelöscht.
-==== Beziehungen hinzufügen (**add**)====
 <code python>
+class HolidayDestination:
+    def __init__(self, location):
+        self._location = location
+        self._people = []
+    def __str__(self):
+        output = f'People visiting {self._location}: '
+        for person in self._people:
+            output += f' {person._name},'
+        output += '\n------'
+        return output
+    def add_person(self, person):
+        if not person in self._people:
+            self._people.append(person)
+            person.add_destination(self)
+    def remove_person(self, person):
+        if person in self._people:
+            self._people.remove(person)
+            person.remove_destination(self)
+class Person:
+    def __init__(self, name):
+        self._name = name
+        self._destinations = []
+    def __str__(self):
+        output = f'{self._name} is visting'
+        for destination in self._destinations:
+            output += f' {destination._location},'
+        output += '\n------'
+        return output
+    def add_destination(self, destination):
+        if not destination in self._destinations:
+            self._destinations.append(destination)
+            destination.add_person(self)
+    def remove_destination(self, destination):
+        if destination in self._destinations:
+            self._destinations.remove(destination)
+            destination.remove_person(self)
+def main():
+    # let's start by creating some people and destinations
+    maya = Person('Maya')
+    thomas = Person('Thomas')
+    jusuf = Person('Jusuf')
+    valley = HolidayDestination('Death valley')
+    atlantis = HolidayDestination('Atlantis')
+    # now we let people visit the destinations
+    maya.add_destination(valley)
+    valley.add_person(thomas)
+    print(valley)
+    atlantis.add_person(maya)
+    jusuf.add_destination(atlantis)
+    print(atlantis)
+    print(maya, thomas, jusuf)
+    # try to add two duplicates
+    jusuf.add_destination(atlantis)
+    atlantis.add_person(maya)
+    print(atlantis)
+    # and now some people are cancelling their vacation
+    valley.remove_person(thomas)
+    print (valley)
+    jusuf.remove_destination(atlantis)
+    print (jusuf)
+    # finally we try to remove non-existing relationships
+    atlantis.remove_person(thomas)
+    print(atlantis)
+    jusuf.remove_destination(valley)
+    print (jusuf)
+if __name__ == '__main__':
+    main()
 </code>
 <WRAP center round tip 60%>
-Je nach Entwurf der Applikation können die **take**- und **remove**-Methoden auch nur einen der Parameter ''index'' bzw. ''key'' anbieten.
+Natürlich könnte man die Methoden auch so anpassen, dass sie als Parameter einen Index, einen Key und/oder ein Objekt akzeptieren.
 </WRAP>