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Mongo - Mongoose

Lesson Objectives#

  1. Explain what an ODM is
  2. Create a Schema for a collection
  3. Create a model and save it
  4. Find a specific model
  5. Update a model already in the database
  6. Remove a model already in the database
  7. Combine Actions

Explain what an ODM is#

ODM stands for Object Document Model. It translates the "documents" being stored in Mongo into fancier JS objects that have more helpful methods and properties.

Create a Schema for a collection#

In mongo, you can put whatever you want into your collections. This can be a little dangerous because you might make a mistake in your code. To avoid having the wrong kind of data in your database, Mongoose allows us to create Schemas (or blueprints) for our objects, so that something funny doesn't find its way in.

First install the npm package

npm install mongoose --save
const mongoose = require("mongoose"); //require mongoose packageconst Schema = mongoose.Schema; //mongoose has many properties on it.  One is a constructor function for Schemas
const articleSchema = new Schema({  title: { type: String, required: true, unique: true }, //can say whether we want properties to be required or unique  author: { type: String, required: true },  body: String,  comments: [{ body: String, commentDate: Date }], // can have arrays of objects with specific properties  publishDate: { type: Date, default: Date.now }, // can set defaults for properties  hidden: Boolean,  meta: {    // can have properties that are objects    votes: Number,    favs: Number,  },});
//Creating an Article class -- will be stored in 'articles' collection.  Mongo does this for you automaticallyconst Article = mongoose.model("Article", articleSchema);
module.exports = Article;

Here are the most common types of properties you can have

  1. String
  2. Number
  3. Date
  4. Boolean
  5. Mixed
  6. ObjectId
  7. Array

Create a model and save it#

Now that we have an Article class, we should import it in another file and use it to create a new Article in our DB. Remember, all the Article class does is set up the blueprint that all article objects must follow. It doesn't create anything in the DB.

const mongoose = require("mongoose");const db = mongoose.connection;const Article = require("./article.js");
//connect to mongomongoose.connect("mongodb://localhost:27017/example");
//if the connection failsdb.on("error", () => {  console.log("error");});
db.once("open", () => {  //we're connected!  //save article to the database  Article.create(    {      title: "Awesome Title",      author: "Matt",    },    (err, article) => {      if (err) {        //if there's an error, log it        console.log(err);      } else {        //else log the created article        console.log(article);      }      mongoose.connection.close(); //close the connection so that the program will end    }  );});

Find a specific model#

The Article class itself has functions that you can call. Note this is not a specific instance of an article, but rather the class.

Mongoose's find method is pretty similar Mongo's, except you need to pass it a callback function to be executed when the data comes back.

Article.find({ author: "Matt" }, (err, articles) => {  console.log(articles); // an array of articles});

Update a model already in the database#

Mongoose's update method is pretty similar Mongo's, except you need to pass it a callback function to be executed when the update is complete.

Article.update(  { author: "Matt" },  { $set: { author: "Matthew" } },  { multi: true },  (err, response) => {    console.log(response); //just tells you the action was successful  });

Remove a model already in the database#

Mongoose's remove method is pretty similar Mongo's, except you need to pass it a callback function to be executed when the remove is complete.

Article.remove({ author: "Matt" }, (err, response) => {  console.log(response); //just tells you the action was successful});

Combine Actions#

The following will not work as expected (create an article and then remove it):

Article.create(  {    title: "Awesome Title",    author: "Matt",  },  (err, article) => {    if (err) {      //if there's an error, log it      console.log(err);    } else {      //else log the created article      console.log(article);    }  });Article.remove({ author: "Matt" }, (err, response) => {  console.log(response); //just tells you the action was successful});

Instead, you'll have to execute the second command in the callback of the first

Article.create(  {    title: "Awesome Title",    author: "Matt",  },  (err, article) => {    if (err) {      //if there's an error, log it      console.log(err);    } else {      //else log the created article      Article.remove({ author: "Matt" }, (err, response) => {        console.log(response); //just tells you the action was successful        mongoose.connection.close(); //close the connection so that the program will end      });    }  });