CRUD Operations

Create, Read, Update, and Delete are the four operations every application performs constantly, and MongoDB gives each one a small, consistent family of methods. Getting comfortable with the "One" vs "Many" variants and their option objects covers the vast majority of day-to-day database work.

Create: insertOne and insertMany

`insertOne()` adds a single document to a collection and returns an acknowledgment containing the generated (or supplied) "_id". `insertMany()` inserts an array of documents in one round trip, which is both more convenient and significantly faster than looping over `insertOne()` for bulk data, since it avoids one network round trip per document.

queries.js

Inserting one document, then several at once

db.users.insertOne({ name: "Ada", age: 30 })

db.users.insertMany([
  { name: "Grace", age: 45 },
  { name: "Alan", age: 41 },
  { name: "Katherine", age: 38 }
])

Inserting one document, then several at once

Read: find and findOne

`find(query)` returns a cursor over every document matching the query filter (an empty object `{}` matches everything), which you typically iterate, convert with `.toArray()`, or chain further with `.sort()`, `.limit()`, and `.skip()`. `findOne(query)` returns only the first matching document (or null), which is convenient when you expect at most one result, such as a lookup by a unique field.

queries.js

Filtering, sorting, and limiting a query

db.users.find({ age: { $gte: 40 } })
  .sort({ age: -1 })
  .limit(2)

// Only one document expected
db.users.findOne({ name: "Ada" })

Filtering, sorting, and limiting a query

Update: updateOne, updateMany, and Update Operators

`updateOne(filter, update)` modifies the first document matching the filter; `updateMany(filter, update)` modifies every matching document. The update argument is not a plain replacement document (by default) - it uses update operators like `$set` (change or add fields), `$inc` (increment a number), `$unset` (remove a field), and `$push` (append to an array) to describe precisely what should change, leaving the rest of the document untouched.

Passing `{ upsert: true }` as an option turns the update into an "update or insert": if no document matches the filter, MongoDB inserts a new one built from the filter and update instead of doing nothing.

queries.js

Targeted field updates vs. an upsert

db.users.updateOne(
  { name: "Ada" },
  { $set: { age: 31 }, $push: { tags: "updated" } }
)

db.users.updateMany(
  { age: { $lt: 18 } },
  { $set: { status: "minor" } }
)

// Insert if no match, update if one exists
db.settings.updateOne(
  { userId: "u1" },
  { $set: { theme: "dark" } },
  { upsert: true }
)

Targeted field updates vs. an upsert

Delete: deleteOne and deleteMany

`deleteOne(filter)` removes the first document matching the filter; `deleteMany(filter)` removes every matching document, and passing `{}` to `deleteMany` removes every document in the collection - a command worth double-checking before running against production data.

queries.js

Deleting matched documents

db.users.deleteOne({ name: "Alan" })

db.users.deleteMany({ status: "inactive" })

Deleting matched documents

Coding challenge

Insert two task documents into a "tasks" collection (each with a "title" and "done: false"), mark one of them as done using $set, then delete every task where "done" is true.

// Write your solution here

Answer every question below to mark this chapter as complete.

Quiz Yourself

Score: 0/4

1. What is the main advantage of insertMany() over calling insertOne() repeatedly in a loop?

2. What does the $set operator do inside an update?

3. What does passing { upsert: true } to updateOne() accomplish?

4. What happens if you call db.users.deleteMany({}) ?