What is mongoose?

• Mongoose is ODM (Object Document Modeling - or Mapping) that is used to connect MongoDB to our web project.
  • 關於 ORM/ODM 討論，可參考: 1. 2.
• SQL used ORM (Object Relational Modeling ), NoSQL used ODM.
• it's a module in npmJS.

Model and Schema

• Everything in Mongoose starts with a schema. Each Schema connect to a MongoDB collection and define the shape of the documents within that collections.
  • 每個 schema 對應到一個 collection( model ), 並定義裡面的物件資料架構
• 'Models' are higher order constructors that take a schema and create an instance of a document equivalent to records in a database. (That's why we don't do finding in schema, instead, we do finding in model.)
  • Schema 定義 model 的 shape
• Model is just like a table in SQL, and schema is the creating table step.
  • model(Mongoose) ≒ collection(MongoDB) ≒ table(SQL)

Connect to MongoDB

// import mod
const express = require('express');
const app = express();
const mongoose = require('mongoose');

// connect to MongoDB
mongoose
	[.connect('mongodb://localhost/todo-list', { 
		useNewUrlParser: true, 
		useUnifiedTopology: true 
	}).](<https://mongoosejs.com/>)then(() => {
		console.log('Connected to Mongo DB.');
	}).catch((e) => {
		console.log('Connection failed.');
		console.log(e);
	});

Define a schema instance(model)

// define a schema of a students model(collection)
const studentSchema = new mongoose.schema({
	name: String,
	age: Number,
	major: String,
	scholarship: {
		merit: Number,
		other: Number,
	},
});

// create a model for students 將 Student 賦值為一個 studentSchema 型的實例物件
// 並且這個 model(collection) 會適用 mongoose 和 mongoDB 的方法
const Student = mongoose.model('Student', studentSchema);

Create An Object instance of model

// create an object of Student collection
// 這邊的做法就跟 JS 創建實例一樣，創建一個適用於 Student 資料表(collection) 的學生實例
const Andrew = new Student({
	name: "Andrew Wu",
	age: 25,
	major: "IM",
	scholarship: {
		merit: 2500,
		other: 1300
	}
});

Save An instance to MongoDB BY Mongoose