[WIP] Add post statistics (counters) caching

migrations/20171101114954_posts_cached_counters.js

@@ -0,0 +1,84 @@
+export async function up(knex) {
+  /**
+   * Creates INSERT/DELETE triggers which update counters on associated posts.
+   */
+  async function createTriggers(table, countColName) {
+    await knex.raw(`
+      CREATE OR REPLACE FUNCTION cache_post_${countColName}(_post_id uuid) RETURNS void AS $$
+      DECLARE
+        post_${countColName} int;
+      BEGIN
+        SELECT count(*) INTO STRICT post_${countColName}
+          FROM ${table} WHERE post_id = _post_id;
+        UPDATE posts SET ${countColName} = post_${countColName} WHERE id = _post_id;
+      END;
+      $$ LANGUAGE 'plpgsql';
+
+      CREATE OR REPLACE FUNCTION cache_post_${countColName}_on_insert() RETURNS trigger AS $$
+      BEGIN
+        EXECUTE cache_post_${countColName}(NEW.post_id);
+        RETURN NULL;
+      END;
+      $$ LANGUAGE 'plpgsql';
+
+      CREATE TRIGGER ${table}_on_insert_update_count_on_posts
+        AFTER INSERT ON ${table}
+        FOR EACH ROW
+        EXECUTE PROCEDURE cache_post_${countColName}_on_insert();
+
+      CREATE OR REPLACE FUNCTION cache_post_${countColName}_on_delete() RETURNS trigger AS $$
+      BEGIN
+        EXECUTE cache_post_${countColName}(OLD.post_id);
+        RETURN NULL;
+      END;
+      $$ LANGUAGE 'plpgsql';
+
+      CREATE TRIGGER ${table}_on_delete_update_count_on_posts
+        AFTER DELETE ON ${table}
+        FOR EACH ROW
+        EXECUTE PROCEDURE cache_post_${countColName}_on_delete();
+    `);
+  }
+
+  await knex.schema.table('posts', function (table) {
+    table.integer('like_count').default(0);
+    table.integer('fav_count').default(0);
+    table.integer('comment_count').default(0);
+    table.integer('score').default(0);
+  });
+
+  // Set counters
+  await knex.raw(`
+    UPDATE posts SET
+      like_count = (SELECT count(*) FROM likes WHERE post_id = posts.id),
+      fav_count = (SELECT count(*) FROM favourites WHERE post_id = posts.id),
+      comment_count = (SELECT count(*) FROM comments WHERE post_id = posts.id);
+  `);
+
+  // Add triggers
+  await createTriggers('likes', 'like_count');
+  await createTriggers('favourites', 'fav_count');
+  await createTriggers('comments', 'comment_count');
+
+  // TODO: Score
+}
+
+export async function down(knex) {
+  async function destroyTriggers(table, countColName) {
+    await knex.raw(`
+      DROP TRIGGER ${table}_on_insert_update_count_on_posts ON ${table};
+      DROP FUNCTION cache_post_${countColName}_on_insert();
+      DROP TRIGGER ${table}_on_delete_update_count_on_posts ON ${table};
+      DROP FUNCTION cache_post_${countColName}_on_delete();
+      DROP FUNCTION cache_post_${countColName}(_post_id uuid);
+    `);
+  }
+
+  await destroyTriggers('likes', 'like_count');
+  await destroyTriggers('favourites', 'fav_count');
+  await destroyTriggers('comments', 'comment_count');
+
+  await knex.schema.table('posts', function (table) {
+    table.dropColumns(['like_count', 'fav_count', 'comment_count', 'score']);
+  });
+}