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Class 14: Document Database Operations

  • Review: Last Class
  • Database Operations
    • Create
    • Read
    • Update
    • Delete

Review

Review: Database

An organized collection of data.

Examples:

  • Library catalog
  • Phone contacts
  • Music playlist
  • Social media feed

Review: Document Database

A database that stores and manages large volumes of unstructured or semi-structured data as "documents", often in JSON format.

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Document: A self-contained unit of data that represents a single entity. (Typically JSON)

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Collection: A group of documents.

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Database: One or more collections of documents.

Review: MongoDB

MongoDB is a popular document database that uses JSON to represent documents.

Document (Object)​

{
  name: "Asteroid",
  description: "An asteroid is a small
    rocky body that orbits the sun.",
}

Collection (Array of Objects)​

[
  {
    name: "Asteroid",
    description: "An asteroid is a
      small rocky body that orbits
      the sun.",
  },
  {
    name: "Galaxy",
    description: "A galaxy is a
      collection of stars, gas, and
      dust held together by gravity.",
  }
]

Activity: Document Database Schema

Working with your peers (2-4), design a document database schema for Plant Scientist blog (https://plantscientist.wordpress.com/) on the board.

A schema is a plan for how to organize data in a database. Define your schema by creating example JSON documents and collections on the board.

Important Observations:

  • The blog has many posts.
  • Each post has a title, content, author, etc.
  • Every post has zero or more comments.
  • Some comment have replies, and some do not.

Review: MongoDB Shell

mongosh is a shell interface for MongoDB (file extension: .mongodb.js).

Specifically, it is a JavaScript and Node.js environment for interacting with MongoDB databases.

use('app')

db.space.drop()
db.createCollection('space')

db.questions.drop()
db.createCollection('questions')

Database Operations

Primary Database Operations


Create - Insert new documents into a collection.

Read - Query and retrieve documents from a collection.

Update - Modify existing documents in a collection.

Delete - Remove documents from a collection.

MongoDB CRUD Operations

Use the reference documentation!

https://www.mongodb.com/docs/manual/crud/

Create

Insert a single document into a collection:

db.TODO_COLLECTION_NAME.insertOne(TODO_DOCUMENT)

Insert multiple documents into a collection:

db.TODO_COLLECTION_NAME.insertMany([
  TODO_DOCUMENT_1,
  TODO_DOCUMENT_2,
  ...
])

Example: Inserting Documents

db.space.insertOne({
  name: "Galaxy",
  description: "A galaxy is a collection of stars, gas, and dust held together by gravity.",
  source: "Microsoft Copilot"
})

db.space.insertMany([
  {
    name: "Asteroid",
    description: "An asteroid is a small rocky body that orbits the sun.",
    source: "Microsoft Copilot"
  },
  {
    name: "Black Hole",
    description: "A black hole, a region of space where gravity is so strong that nothing can escape it.",
    source: "Microsoft Copilot",
  },
])

Activity: Insert Document into MongoDB

Working with your peers (2-4), initialize a produce collection into the playground database using the existing data in playground.mongodb.js


db.produce.insertOne({...})
db.produce.insertMany([ {...},{...}, ... ])

Gotcha: Set the Database!

MongoDB Shell defaults to the test database. Always make sure to set the database before running any commands!

use('app')

Read: Querying Documents

Retrieve all documents from a collection:

db.TODO_COLLECTION_NAME.find()

Retrieve documents that match a specific condition:

db.TODO_COLLECTION_NAME.find({ FIELD: VALUE })

Retrieve documents that match multiple conditions:

db.TODO_COLLECTION_NAME.find({ FIELD1: VALUE1, FIELD2: VALUE2 })

Example: Querying Documents

// Find all documents in the "space" collection
db.space.find()

// Find all documents where the name is "Galaxy"
db.space.find({ name: "Galaxy" })

Interactive MongoDB Shell

.mongodb.js files are useful for initializing a database (i.g. init.mongodb.js), but they are not ideal for testing queries.

Solution: Use the interactive mongosh shell to test your queries.

  1. Open a Terminal.
  2. Run the command: mongosh
  3. Set the database: use('app')
  4. Test your queries!
  5. When you're done, exit the shell by running: exit

Activity: Query Documents in MongoDB

Together, let's retrieve all documents from the produce, space, and questions collections.

MongoDB Query Operators

db.TODO_COLLECTION_NAME.find({ FIELD: { OPERATOR: VALUE } })
OperatorDescription
$eqEqual to
$neNot equal to
$gtGreater than
$gteGreater than or equal to
$ltLess than
$lteLess than or equal to

Example: Query Operators

// Find all documents that are not "Galaxy"
db.space.find({ name: { $ne: "Galaxy" } })

Note: $eq is the default operator. These queries are equivalent:

db.space.find({ name: "Galaxy" })
db.space.find({ name: { $eq: "Galaxy" } })

Activity: Query with Operators in MongoDB

Working with your peers, complete items #1 and #2 on the handout.

Use mongosh to test your queries, then write your answer on the handout.

Example:

// Find all documents that are not "Galaxy"
db.space.find({ name: { $ne: "Galaxy" } })

Update: Modifying Documents

Update a single document:

db.TODO_COLLECTION_NAME.updateOne(
  { FIELD: VALUE }, // Filter
  { $set: { FIELD_TO_UPDATE: NEW_VALUE } } // Update
)

Update multiple documents:

db.TODO_COLLECTION_NAME.updateMany(
  { FIELD: VALUE }, // Filter
  { $set: { FIELD_TO_UPDATE: NEW_VALUE } } // Update
)

Update Operators

db.TODO_COLLECTION_NAME.updateOne(
  { FIELD: VALUE }, // Filter
  { UPDATE_OPERATOR: { FIELD_TO_UPDATE: NEW_VALUE } } // Update
)
OperatorDescription
$setSet the value of a field
$incIncrement the value of a field
$pushAdd an item to an array field
$pullRemove an item from an array field

Activity: Update Documents in MongoDB

Working with your peers, complete item #3 on the handout.

Use mongosh to test your queries, then write your answer on the handout.

Example:

db.space.updateOne(
  { name: "Galaxy" },
  { $set: { description: "A galaxy is a massive system of stars,
    gas, and dust held together by gravity." } }
)

Delete: Removing Documents

Delete a single document:

db.TODO_COLLECTION_NAME.deleteOne({ FIELD: VALUE })

Delete multiple documents:

db.TODO_COLLECTION_NAME.deleteMany({ FIELD: VALUE })

Activity: Delete Documents in MongoDB

Working with your peers, complete item #4 on the handout.

Use mongosh to test your queries, then write your answer on the handout.


// Delete the "Galaxy" document
db.space.deleteOne({ name: "Galaxy" })

Project 2

Project 2: Community Events SPA

For your second project you will design and implement an interactive community events single-page application using the MERN stack. For this project, you may only use the methods taught in this course.

The idea for this project to encourage community engagement by providing a platform for community members to discover and participate in local events. However, community engagement is not a strict requirement for this project. You may create an events web application for any type of events you like regardless of whether it promotes community engagement.

Summary

  • The primary database operations are Create, Read, Update, and Delete (CRUD).
  • Create inserts new documents into a collection.
  • Read queries and retrieves documents from a collection.
  • Update modifies existing documents in a collection.
  • Delete removes documents from a collection.

What's Next

Wednesday: Project 2, Milestone 1 Released

Friday: Practice Problem Workshop (Document Databases)

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