mongoose_sandbox.js

const mongoose = require('mongoose')

mongoose.connect('mongodb://localhost:27017/sandbox')
const db = mongoose.connection

db.on('error', (err) => console.error('connection error:', err))

db.once('open', () => {
  console.log('db connection successful')
  // All database communication goes here

  const Schema = mongoose.Schema
  const AnimalSchema = new Schema({
    type: { type: String, default: 'goldfish' },
    size: String,
    color: { type: String, default: 'golden' },
    mass: { type: Number, default: 0.007 },
    name: { type: String, default: 'Angela' },
  })

  AnimalSchema.pre('save', function(next) {
    if (this.mass >= 100) {
      this.size = 'big'
    } else if (this.mass >= 5 && this.mass < 100) {
      this.size = 'medium'
    } else {
      this.size = 'small'
    }
    next()
  })

  AnimalSchema.statics.findSize = function(size, callback) {
    return this.find({ size }, callback) // this == Animal
  }

  AnimalSchema.methods.findSameColor = function(callback) {
    return this.model('Animal').find({ color: this.color }, callback) // this == document
  }

  const Animal = mongoose.model('Animal', AnimalSchema)

  const elephant = new Animal({
    type: 'elephant',
    color: 'gray',
    mass: 6000,
    name: 'Lawrence',
  })

  const animal = new Animal({}) // Goldfish

  const whale = new Animal({
    type: 'whale',
    mass: 190500,
    name: 'Fig',
  })

  const animalData = [
    {
      type: 'mouse',
      color: 'gray',
      mass: 0.035,
      name: 'Marvin',
    },
    {
      type: 'nutria',
      color: 'brown',
      mass: 6.35,
      name: 'Gretchen',
    },
    {
      type: 'wolf',
      color: 'gray',
      mass: 45,
      name: 'Iris',
    },
    elephant,
    animal,
    whale,
  ]

  Animal.remove({}, (err) => {
    if (err) console.error(err)
    Animal.create(animalData, (err, animals) => {
      if (err) console.error(err)
      Animal.findOne({ type: 'elephant' }, (err, elephant) => {
        elephant.findSameColor((err, animals) => {
          if (err) console.error(err)

          animals.forEach((animal) => console.log(`${animal.name} the ${animal.color} ${animal.type} is a ${animal.size}-sized animal.`))
          db.close(() => console.log('db connection closed'))
        })
      })
    })
  })
})