Add a materialized view to capture the first time a type has been seen for export

This will make it easier to create an interface which allows exporting events as
they've come up.

migrations/20181026220312-first-types-materialized-view.js

@@ -0,0 +1,11 @@
+'use strict';
+
+module.exports = {
+  up: (queryInterface, Sequelize) => {
+    return queryInterface.sequelize.query('CREATE MATERIALIZED VIEW first_type AS SELECT DISTINCT(type), MIN("createdAt") FROM events GROUP BY type');
+  },
+
+  down: (queryInterface, Sequelize) => {
+    return queryInterface.sequelize.query('DROP MATERIALIZED VIEW first_type');
+  }
+};

src/models/index.ts

@@ -35,4 +35,15 @@ Object.keys(db).forEach(modelName => {
 db.sequelize = sequelize;
 db.Sequelize = Sequelize;
 
+
+/*
+ * Periodically refresh the materialized view for holding the first types
+ */
+setInterval(() => {
+  logger.info('Refreshing the `first_type` materialized view');
+  sequelize.query('REFRESH MATERIALIZED VIEW first_type');
+}, ((60 * 1000) * 60));
+
+
+
 export default db;