Add intro/part1

intro/server/mixins/db.mixin.js

@@ -0,0 +1,31 @@
+"use strict";
+
+const path = require("path");
+const mkdir = require("mkdirp").sync;
+
+const DbService	= require("moleculer-db");
+
+//process.env.MONGO_URI = "mongodb://localhost/conduit";
+
+module.exports = function(collection) {
+	if (process.env.MONGO_URI) {
+		// Mongo adapter
+		const MongoAdapter = require("moleculer-db-adapter-mongo");
+
+		return {
+			mixins: [DbService],
+			adapter: new MongoAdapter(process.env.MONGO_URI),
+			collection
+		};
+	}
+
+	// --- NeDB fallback DB adapter
+	
+	// Create data folder
+	mkdir(path.resolve("./data"));
+
+	return {
+		mixins: [DbService],
+		adapter: new DbService.MemoryAdapter({ filename: `./data/${collection}.db` })
+	};
+};