[api] protect against multiple requests with same number

src/api/db/migrate/20160518105300_uniq_number_index.rb

@@ -0,0 +1,11 @@
+class UniqNumberIndex < ActiveRecord::Migration
+  def self.up
+    remove_index :bs_requests, :number
+    add_index :bs_requests, :number, unique: true
+  end
+
+  def self.down
+    remove_index :bs_requests, :number
+    add_index :bs_requests, :number
+  end
+end

src/api/db/structure.sql

@@ -263,12 +263,12 @@ CREATE TABLE `bs_requests` (
   `updated_at` datetime NOT NULL,
   `accept_at` datetime DEFAULT NULL,
   `priority` enum('critical','important','moderate','low') COLLATE utf8_bin DEFAULT 'moderate',
-  `number` int(11) DEFAULT NULL,
+  `number` int(11) NOT NULL,
   PRIMARY KEY (`id`),
+  UNIQUE KEY `index_bs_requests_on_number` (`number`),
   KEY `index_bs_requests_on_creator` (`creator`),
   KEY `index_bs_requests_on_state` (`state`),
-  KEY `index_bs_requests_on_superseded_by` (`superseded_by`),
-  KEY `index_bs_requests_on_number` (`number`)
+  KEY `index_bs_requests_on_superseded_by` (`superseded_by`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
 
 CREATE TABLE `cache_lines` (
@@ -1678,6 +1678,8 @@ INSERT INTO schema_migrations (version) VALUES ('20160321104000');
 
 INSERT INTO schema_migrations (version) VALUES ('20160321105300');
 
+INSERT INTO schema_migrations (version) VALUES ('20160518105300');
+
 INSERT INTO schema_migrations (version) VALUES ('21');
 
 INSERT INTO schema_migrations (version) VALUES ('22');