Add unique constraint on Finding Evidence

db/migrate/20211130205719_add_uniqueness_for_evidence_occurrence_id.rb

+# frozen_string_literal: true
+
+class AddUniquenessForEvidenceOccurrenceId < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'finding_evidences_on_vulnerability_occurrence_id'
+  UNIQUE_INDEX_NAME = 'finding_evidences_on_unique_vulnerability_occurrence_id'
+
+  def up
+    add_concurrent_index :vulnerability_finding_evidences, [:vulnerability_occurrence_id], unique: true, name: UNIQUE_INDEX_NAME
+    remove_concurrent_index :vulnerability_finding_evidences, [:vulnerability_occurrence_id], name: INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :vulnerability_finding_evidences, [:vulnerability_occurrence_id], name: INDEX_NAME
+    remove_concurrent_index :vulnerability_finding_evidences, [:vulnerability_occurrence_id], name: UNIQUE_INDEX_NAME
+  end
+end

db/schema_migrations/20211130205719

+567a80916756adcca93bdbe82d69a923e539aac74146e714b58a1b023134d2c9
\ No newline at end of file

db/structure.sql

@@ -25035,7 +25035,7 @@ CREATE INDEX finding_evidence_sources_on_finding_evidence_id ON vulnerability_fi
 
 CREATE INDEX finding_evidence_supporting_messages_on_finding_evidence_id ON vulnerability_finding_evidence_supporting_messages USING btree (vulnerability_finding_evidence_id);
 
-CREATE INDEX finding_evidences_on_vulnerability_occurrence_id ON vulnerability_finding_evidences USING btree (vulnerability_occurrence_id);
+CREATE UNIQUE INDEX finding_evidences_on_unique_vulnerability_occurrence_id ON vulnerability_finding_evidences USING btree (vulnerability_occurrence_id);
 
 CREATE INDEX finding_links_on_vulnerability_occurrence_id ON vulnerability_finding_links USING btree (vulnerability_occurrence_id);