Insert with arrays in MongoDB

Introduction

We use insert with arrays to add many items to a database at once. It saves time and keeps data organized.

When you want to add a list of new users to your app all at once.

When you have many product details to add to your store database.

When you collect multiple survey answers and want to save them together.

When you want to quickly add many blog posts or articles.

When you receive a batch of sensor readings and want to store them.

Syntax

MongoDB

db.collection.insertMany([
  { document1 },
  { document2 },
  ...
])

Use insertMany() to add multiple documents (items) at once.

Each document is inside curly braces { } and separated by commas.

Examples

Inserts two fruit documents into the fruits collection.

MongoDB

db.fruits.insertMany([
  { name: "Apple", color: "Red" },
  { name: "Banana", color: "Yellow" }
])

Inserts an empty array, which means no documents are added.

MongoDB

db.students.insertMany([])

Inserts one book document using insertMany with a single item array.

MongoDB

db.books.insertMany([
  { title: "Book One", author: "Author A" }
])

Sample Program

This program creates a 'students' collection, inserts three student records at once, prints their new IDs, and then prints all students in the collection.

MongoDB

use school

db.students.drop()

// Insert multiple student records
const result = db.students.insertMany([
  { name: "Alice", age: 14, grade: 9 },
  { name: "Bob", age: 15, grade: 10 },
  { name: "Charlie", age: 14, grade: 9 }
])

// Show inserted IDs
printjson(result.insertedIds)

// Show all students
const allStudents = db.students.find().toArray()
printjson(allStudents)

Important Notes

insertMany() is faster than inserting one document at a time.

By default (ordered: true), if one document fails, preceding documents are inserted but subsequent ones are not.

Remember to check the result to confirm all documents were added.

Summary

Use insertMany() to add multiple documents to a MongoDB collection at once.

Documents are passed as an array inside insertMany().

This method helps save time and keeps data organized.

Practice

1. What does the insertMany() method do in MongoDB?

easy

A. Inserts multiple documents into a collection at once

B. Deletes multiple documents from a collection

C. Updates multiple documents in a collection

D. Finds multiple documents in a collection

Solution

1. Step 1: Understand the purpose of insertMany()

   The insertMany() method is used to add several documents to a MongoDB collection in one operation.

2. Step 2: Compare with other operations

   Deleting, updating, or finding documents are done by other methods like deleteMany(), updateMany(), and find().

3. Final Answer:

   Inserts multiple documents into a collection at once -> Option A

4. Quick Check:

   insertMany() = Inserts multiple documents [OK]

Hint: insertMany() adds many documents in one call [OK]

Common Mistakes:

• Confusing insertMany() with update or delete methods
• Thinking insertMany() inserts only one document
• Assuming insertMany() returns documents instead of inserting

2. Which of the following is the correct syntax to insert multiple documents using insertMany()?

easy

A. db.collection.insertMany('name: Alice', 'name: Bob')

B. db.collection.insertMany({name: 'Alice'}, {name: 'Bob'})

C. db.collection.insertMany([{name: 'Alice'}, {name: 'Bob'}])

D. db.collection.insertMany(name: 'Alice', name: 'Bob')

Solution

1. Step 1: Check the parameter type for insertMany()

   The method requires an array of documents, so the argument must be inside square brackets [].

2. Step 2: Validate the options

   Only db.collection.insertMany([{name: 'Alice'}, {name: 'Bob'}]) correctly passes an array of objects. The other options pass multiple arguments or wrong types, causing syntax errors.

3. Final Answer:

   db.collection.insertMany([{name: 'Alice'}, {name: 'Bob'}]) -> Option C

4. Quick Check:

   insertMany() needs an array of documents [OK]

Hint: Use square brackets [] to pass multiple documents [OK]

Common Mistakes:

• Passing documents without array brackets
• Using multiple arguments instead of one array
• Using strings instead of objects for documents

3. What will be the result of this code?

db.users.insertMany([
  {name: 'John', age: 25},
  {name: 'Jane', age: 30}
])
const count = db.users.countDocuments()

medium

A. Syntax error occurs

B. count will be 1

C. count will be 0

D. count will be 2

Solution

1. Step 1: Understand insertMany() effect

   The insertMany() call inserts two documents into the users collection.

2. Step 2: Count documents after insertion

   The countDocuments() method returns the total number of documents in the collection, which is 2 after insertion.

3. Final Answer:

   count will be 2 -> Option D

4. Quick Check:

   2 documents inserted, countDocuments() = 2 [OK]

Hint: insertMany() adds all docs; countDocuments() counts them [OK]

Common Mistakes:

• Assuming countDocuments() runs before insertMany() completes
• Thinking insertMany() inserts only one document
• Confusing countDocuments() with count() method

4. Identify the error in this MongoDB insertMany() usage:

db.products.insertMany(
  {name: 'Pen', price: 1.5},
  {name: 'Pencil', price: 0.5}
)

medium

A. insertMany() cannot insert more than one document

B. Missing array brackets around documents

C. Documents have invalid field names

D. Using insertOne() instead of insertMany()

Solution

1. Step 1: Check the argument format for insertMany()

   The method requires a single array containing all documents, but here documents are passed as separate arguments.

2. Step 2: Identify the fix

   Wrapping the documents inside square brackets [] fixes the syntax: insertMany([{...}, {...}]).

3. Final Answer:

   Missing array brackets around documents -> Option B

4. Quick Check:

   insertMany() needs an array of documents [OK]

Hint: Always wrap multiple docs in [] for insertMany() [OK]

Common Mistakes:

• Passing multiple documents as separate arguments
• Confusing insertMany() with insertOne()
• Assuming insertMany() accepts objects directly without array

5. You want to insert a list of users but only those with an age above 18. Which MongoDB operation correctly inserts only the valid users?

const users = [
  {name: 'Anna', age: 17},
  {name: 'Ben', age: 20},
  {name: 'Cara', age: 22}
];
// Which code inserts only users older than 18?

hard

A. db.users.insertMany(users.filter(u => u.age > 18))

B. db.users.insertMany(users)

C. db.users.insertMany(users.map(u => u.age > 18))

D. db.users.insertMany(users.filter(u => u.age < 18))

Solution

1. Step 1: Filter users by age before insertion

   Use JavaScript's filter() to keep only users with age greater than 18.

2. Step 2: Pass filtered array to insertMany()

   Passing the filtered array inserts only valid users. Inserting all users includes invalid ones, mapping to booleans creates invalid documents, and filtering under 18 selects the wrong users.

3. Final Answer:

   db.users.insertMany(users.filter(u => u.age > 18)) -> Option A

4. Quick Check:

   Filter first, then insertMany() [OK]

Hint: Filter array before insertMany() to insert selected docs [OK]

Common Mistakes:

• Inserting all users without filtering
• Using map instead of filter, causing wrong data
• Filtering with wrong condition (age < 18)