Why advanced updates matter in MongoDB - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the age of a user named 'Alice' to 30.

MongoDB

db.users.updateOne({name: 'Alice'}, {$set: {age: [1])

Drag options to blanks, or click blank then click option'

A25

B30

C35

D40

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong age value.

Forgetting to use $set operator.

The $set operator updates the specified field. Here, we set age to 30.

2fill in blank

medium

Complete the code to increment the score of a player named 'Bob' by 10.

MongoDB

db.players.updateOne({name: 'Bob'}, {$inc: {score: [1])

Drag options to blanks, or click blank then click option'

A5

B20

C10

D15

Attempts:

3 left

💡 Hint

Common Mistakes

Using $set instead of $inc.

Using wrong increment value.

The $inc operator increases the value of the field by the specified amount. Here, we increment score by 10.

3fill in blank

hard

Fix the error in the update code to add a new tag 'urgent' to the tags array for task with id 123.

MongoDB

db.tasks.updateOne({_id: 123}, {$push: {tags: [1])

Drag options to blanks, or click blank then click option'

A'urgent'

Burgent

C{urgent}

D[urgent]

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the string value.

Using curly braces or brackets incorrectly.

Strings in MongoDB update queries must be quoted. So, 'urgent' is correct to add the tag.

4fill in blank

hard

Fill both blanks to update the price to 19.99 and set the status to 'available' for product with id 456.

MongoDB

db.products.updateOne({_id: 456}, {$set: {price: [1], status: [2])

Drag options to blanks, or click blank then click option'

A19.99

B'available'

C'sold out'

D20.99

Attempts:

3 left

💡 Hint

Common Mistakes

Quoting numbers or not quoting strings.

Using wrong values for price or status.

Price is a number so no quotes needed. Status is a string and must be quoted.

5fill in blank

hard

Fill all three blanks to update the user's email, increment login count by 1, and add 'premium' to roles array for user with username 'jane'.

MongoDB

db.users.updateOne({username: 'jane'}, {$set: {email: [1], $inc: {logins: [2], $push: {roles: [3])

Drag options to blanks, or click blank then click option'

A'[e-mail]'

B1

C'premium'

D'[e-mail]'

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting strings, wrong increment value, or wrong email.

Email is a string and must be quoted. Login increment is numeric. Role added is a string and must be quoted.

Practice

1. What is the main benefit of using advanced update operators like $set and $inc in MongoDB?

easy

A. They convert documents into arrays.

B. They automatically create new collections.

C. They delete documents faster than normal deletes.

D. They allow updating multiple fields in a single command.

Solution

1. Step 1: Understand update operators purpose

   Operators like $set and $inc let you change specific fields without replacing the whole document.

2. Step 2: Recognize efficiency in updates

   Using these operators, you can update many fields at once, saving time and keeping data accurate.

3. Final Answer:

   They allow updating multiple fields in a single command. -> Option D

4. Quick Check:

   Advanced updates = multiple fields updated at once [OK]

Hint: Advanced updates change many fields in one go [OK]

Common Mistakes:

• Thinking updates create new collections
• Confusing update with delete operations
• Believing updates convert data types automatically

2. Which of the following is the correct syntax to increment a field named score by 5 in MongoDB?

easy

A. { $add: { score: 5 } }

B. { $set: { score: +5 } }

C. { $inc: { score: 5 } }

D. { $push: { score: 5 } }

Solution

1. Step 1: Identify the operator for increment

   The $inc operator is used to increase a numeric field by a specified amount.

2. Step 2: Check syntax correctness

   The correct syntax is { $inc: { score: 5 } }. Other options use wrong operators or syntax.

3. Final Answer:

   { $inc: { score: 5 } } -> Option C

4. Quick Check:

   Increment uses $inc with field and value [OK]

Hint: Use $inc to add numbers, syntax: { $inc: { field: value } } [OK]

Common Mistakes:

• Using $set with +5 instead of $inc
• Using $push which is for arrays
• Using non-existent $add operator

3. Given the document { _id: 1, tags: ["red", "blue"] }, what will be the result after running db.collection.updateOne({ _id: 1 }, { $push: { tags: "green" } })?

medium

A. { _id: 1, tags: ["red", "blue", "green"] }

B. { _id: 1, tags: ["red", "blue"] }

C. { _id: 1, tags: "green" }

D. Error: $push cannot be used on arrays

Solution

1. Step 1: Understand $push operator effect

   The $push operator adds an element to the end of an array field.

2. Step 2: Apply $push to the tags array

   Adding "green" to the existing array ["red", "blue"] results in ["red", "blue", "green"].

3. Final Answer:

   { _id: 1, tags: ["red", "blue", "green"] } -> Option A

4. Quick Check:

   $push adds item to array end [OK]

Hint: Use $push to add items to arrays [OK]

Common Mistakes:

• Thinking $push replaces the array
• Expecting $push to error on arrays
• Confusing $push with $set

4. What is wrong with this update command?

db.collection.updateOne({ _id: 2 }, { score: 10 })

medium

A. The filter {_id: 2} is invalid.

B. Missing update operator like $set before the field.

C. The value 10 must be a string.

D. updateOne cannot update a single document.

Solution

1. Step 1: Check update command structure

   MongoDB update commands require an update operator like $set to specify fields to change.

2. Step 2: Identify missing operator

   The command uses { score: 10 } directly without $set, causing an error.

3. Final Answer:

   Missing update operator like $set before the field. -> Option B

4. Quick Check:

   Update needs $set or similar operator [OK]

Hint: Always use $set or $inc for field updates [OK]

Common Mistakes:

• Omitting $set operator
• Thinking filter {_id: 2} is wrong
• Believing numeric values must be strings

5. You want to update a user's document to increase their points by 10, add a new tag "vip" to their tags array only if it does not exist, and set their status to "active". Which update command achieves all this in one operation?

hard

A. { $inc: { points: 10 }, $addToSet: { tags: "vip" }, $set: { status: "active" } }

B. { $inc: { points: 10 }, $pushAll: { tags: ["vip"] }, $set: { status: "active" } }

C. { $inc: { points: 10 }, $push: { tags: "vip" }, $set: { status: "active" } }

D. { $set: { points: 10, tags: "vip", status: "active" } }

Solution

1. Step 1: Identify operator to increment points

   Use $inc to add 10 to the points field.

2. Step 2: Add "vip" tag only if not present

   $addToSet adds an item to an array only if it doesn't already exist, perfect for tags.

3. Step 3: Set status to "active"

   $set updates the status field to "active".

4. Final Answer:

   { $inc: { points: 10 }, $addToSet: { tags: "vip" }, $set: { status: "active" } } -> Option A

5. Quick Check:

   Use $inc, $addToSet, and $set together [OK]

Hint: Use $addToSet to avoid duplicate array items [OK]

Common Mistakes:

• Using $push instead of $addToSet causing duplicates
• Using $pushAll which is deprecated
• Setting points directly instead of incrementing