Change service to site to m2m relation

django_backend/backend/models.py

@@ -122,7 +122,7 @@ def deregister_at_rabbitmq(
 class Service(models.Model):
     name = models.CharField(max_length=150, unique=True)
     description = models.TextField(max_length=300, blank=True)
-    site = models.ForeignKey(
+    site = models.ManyToManyField(
             Site,
             related_name='services')
     groups = models.ManyToManyField(
@@ -131,7 +131,7 @@ class Service(models.Model):
             blank=True)
 
     def __str__(self):
-        return self.name + '@' + self.site.name
+        return self.name + '@' + str(list(self.site.all()))
 
 
 class SSHPublicKey(models.Model):