jwatson3d · February 3, 2020 05:09 · Mar 15, 2013
diff --git a/referenced_mongo_json.md b/referenced_mongo_json.md
@@ -0,0 +1,105 @@
+#### Populating referenced collections in MongoDB from JSON files using Node.js and Mongoose
+
+I recently began working with Node and MongoDB for a small personal project, largely just to learn the technologies. One thing that is fairly simple but that I found far from obvious and lacking in concrete examples was how to populate the part of my database that used referenced collections from the sample JSON data I was starting with. This post attempts to fill that gap using the following code snippets, which are heavily commented inline. You will notice I am using the awesome [Mongoose](http://mongoosejs.com/) library which makes working with MongoDB very easy.
+
+```javascript
+http.createServer( app ).listen( app.get( 'port' ), function() {
+
+    mongoose.connect( 'mongodb://localhost/{YOUR_DB_NAME}' );
+
+	var db = mongoose.connection;
+	db.on( 'error', console.error.bind( console, 'connection error:' ) );
+
+	// once the connection is established we define our schemas
+	db.once( 'open', function callback() {
+
+		// independent schema
+		var FoodSchema = new Schema( {
+			name: String,
+			unit: String,
+			p: Number,
+			f: Number,
+			c: Number
+		} );
+
+		// this schema represents a collection whose documents
+		// will each hold a reference to a single document
+		// from the FoodSchema collection
+		var LogEntrySchema = new Schema( {
+			date: Date,
+			qty: Number,
+			// starting the name with an underscore is simply a convention
+			// to denote this field as a reference
+			// the type instructs Mongoose to set this up as a reference
+			// to another document's _id property, which is automatically
+			// generated by MongoDB. the ref field refers to the Model name
+			_food: { type: Schema.Types.ObjectId, ref: 'Food' }
+		} );
+
+		// create Mongoose models from our schemas
+		var Food = mongoose.model( 'Food', FoodSchema );
+		var LogEntry = mongoose.model( 'LogEntry', LogEntrySchema );
+
+	} );
+
+} );
+```
+
+During development I simply defined a route that I could load to trigger a database rebuild. This proved very useful as I would regularly muck things up while working on a new form or other piece of the app. Below is the code for (re)populating the database from JSON files.
+
+```javascript
+var mongoose = require( 'mongoose' )
+    , _ = require( 'lodash' )
+	, foodData = require( './mockdata/foodData.json' )
+	, logData = require( './mockdata/logData.json' );
+
+exports.reset = function( req, res ) {
+
+	// get refs to the models we defined above
+	var Food = mongoose.model( 'Food' );
+	var LogEntry = mongoose.model( 'LogEntry' );
+
+	// clear all existing documents from the collections
+	Food.find().remove();
+	LogEntry.find().remove();
+
+	// populate the foods collection from json data
+	// nothing fancy here as Food documents do not reference anything else
+	for( var i = 0; i < foodData.length; i++ ) {
+		new Food( foodData[ i ] ).save();
+	}
+
+	// now that the collection is populated we iterate over it
+	Food.find( function( err, foods ) {
+		var foodMap = {};
+
+		// store _ids of Food documents that Mongo generated upon insert
+		for( var i = 0; i < foods.length; i++ ) {
+			var food = foods[i];
+			// I am mapping the ids to the food names because the LogEntry
+			// JSON data contained this field thanks to the original source
+			// data's structure (a spreadsheet).
+			// You could utilize a more sophisticated lookup here if necessary.
+			foodMap[ food.name ] = food._id;
+		}
+
+		// populate the LogEntries collection from json data
+		for( i = 0; i < logData.length; i++ ) {
+			var logEntry = logData[ i ];
+			// we find and store food._id on LogEntry for reference
+			logEntry._food = foodMap[ logEntry.food_name ];
+
+			// note that only the fields defined in the schema will be
+			// persisted to Mongo, so the foodName field we used for
+			// lookup will not be unnecessarily added to the db
+			new LogEntry( logEntry ).save();
+		}
+	} );
+
+	res.redirect( "/" );
+};
+```
+
+And there you have it. Far from revolutionary, but hopefully it will help someone get up and running a bit more quickly than I did, though I have to say I was pleasantly surprised with how quickly I was able to be productive with these new (to me) technologies. If you have corrections or suggestions for improvement please leave a comment or fork this Gist.
+
+Enjoy!