[Feature] Legacy API Layer (#80)

Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#80

epdb/models.py

@@ -889,6 +889,23 @@ class CompoundStructure(EnviPathModel, AliasMixin, ScenarioMixin, ChemicalIdenti
     def as_svg(self, width: int = 800, height: int = 400):
         return IndigoUtils.mol_to_svg(self.smiles, width=width, height=height)
 
+    @property
+    def related_pathways(self):
+        pathways = Node.objects.filter(node_labels__in=[self]).values_list('pathway', flat=True)
+        return Pathway.objects.filter(package=self.compound.package, id__in=set(pathways)).order_by('name')
+
+    @property
+    def related_reactions(self):
+        return (
+                Reaction.objects.filter(package=self.compound.package, educts__in=[self])
+                |
+                Reaction.objects.filter(package=self.compound.package, products__in=[self])
+        ).order_by('name')
+
+    @property
+    def is_default_structure(self):
+        return self.compound.default_structure == self
+
 
 class Rule(PolymorphicModel, EnviPathModel, AliasMixin, ScenarioMixin):
     package = models.ForeignKey('epdb.Package', verbose_name='Package', on_delete=models.CASCADE, db_index=True)