Enforced unicity of relations between 2 issues with a database index (#9685).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@8041 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/20111201201315_add_unique_index_to_issue_relations.rb

@@ -0,0 +1,16 @@
+class AddUniqueIndexToIssueRelations < ActiveRecord::Migration
+  def self.up
+
+    # Remove duplicates
+    IssueRelation.connection.select_values("SELECT r.id FROM #{IssueRelation.table_name} r" +
+      " WHERE r.id > (SELECT min(r1.id) FROM #{IssueRelation.table_name} r1 WHERE r1.issue_from_id = r.issue_from_id AND r1.issue_to_id = r.issue_to_id)").each do |i|
+        IssueRelation.delete_all(["id = ?", i])
+    end
+
+    add_index :issue_relations, [:issue_from_id, :issue_to_id], :unique => true
+  end
+
+  def self.down
+    remove_index :issue_relations, :column => [:issue_from_id, :issue_to_id]
+  end
+end