[Feature] Management Command to Compute and Store Reaction <-> Rule Associations (#453)

Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#453

epdb/models.py

@@ -1730,6 +1730,14 @@ class SequentialRuleOrdering(models.Model):
     order_index = models.IntegerField(null=False, blank=False)
 
 
+class ReactionExplanation(TimeStampedModel):
+    run_uuid = models.UUIDField(null=False, blank=False)
+    run_start = models.DateTimeField(null=False, blank=False)
+    reaction = models.ForeignKey("epdb.Reaction", on_delete=models.CASCADE)
+    rule = models.ForeignKey("epdb.Rule", on_delete=models.CASCADE)
+    exact = models.BooleanField(default=False)
+
+
 class Reaction(
     EnviPathModel, AliasMixin, ScenarioMixin, ReactionIdentifierMixin, AdditionalInformationMixin
 ):
@@ -1755,6 +1763,12 @@ class Reaction(
 
     external_identifiers = GenericRelation("ExternalIdentifier")
 
+    explained_by = models.ManyToManyField(
+        "epdb.Rule",
+        through="ReactionExplanation",
+        related_name="explained_reactions",
+    )
+
     def _url(self):
         return "{}/reaction/{}".format(self.package.url, self.uuid)