update conditions to use through for self links

atlas/models.py

@@ -144,7 +144,7 @@ class Condition(SynMixin, models.Model):
     name = models.CharField(max_length=255, unique=True)
 
     synonym = models.ManyToManyField("self", blank=True)
-    parent = models.ManyToManyField("self", blank=True)
+    parent = models.ManyToManyField("self", blank=True, related_name="child", symmetrical=False, through="ConditionRelationship")
 
     primary = models.BooleanField(default="True")
 
@@ -157,6 +157,25 @@ class Condition(SynMixin, models.Model):
     def get_absolute_url(self):
         return reverse("atlas:condition_detail", kwargs={"pk": self.pk})
 
+    def get_children(self):
+        return self.child.all()
+
+    def get_descendents(self):
+        """TODO"""
+
+
+    def get_parents(self):
+        return self.parent.all()
+
+class ConditionRelationship(models.Model):
+    child = models.ForeignKey(Condition, on_delete=models.CASCADE)
+    parent = models.ForeignKey(Condition, on_delete=models.CASCADE, related_name="+")
+
+    relationship_type = models.CharField(max_length=255, blank=True, null=True)
+
+    def __str__(self):
+        return f"{self.parent} -> {self.child}"
+    
 
 class Presentation(models.Model):
     name = models.CharField(max_length=255)