deleteOne method in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delete one document where the name is 'Alice'.

MongoDB

db.collection('users').deleteOne({ name: [1] })

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

A'Alice'

BAlice

C"name"

D'name'

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around string values

Using the field name as the value instead of the actual value

The deleteOne method requires a filter object. The value for the name field must be a string, so it needs quotes like 'Alice'.

2fill in blank

medium

Complete the code to delete one document where the age is 30.

MongoDB

db.collection('users').deleteOne({ age: [1] })

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

A'30'

B'age'

C"age"

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Putting numbers inside quotes, making them strings

Using the field name as the value

The age field is a number, so the value should be the number 30 without quotes.

3fill in blank

hard

Fix the error in the code to delete one document where the status is 'active'.

MongoDB

db.collection('users').deleteOne({ status: [1] })

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

A'active'

Bactive

C"status"

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted strings causing reference errors

Confusing field names with values

The value 'active' must be a string with quotes. Without quotes, it is treated as a variable which causes an error.

4fill in blank

hard

Fill both blanks to delete one document where the city is 'Paris' and the age is 25.

MongoDB

db.collection('users').deleteOne({ [1]: [2], age: 25 })

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

Acity

B'Paris'

C'city'

DParis

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around keys incorrectly

Not quoting string values

The filter object needs the field name city without quotes as a key, and the value 'Paris' as a string with quotes.

5fill in blank

hard

Fill all three blanks to delete one document where the first name is 'John', last name is 'Doe', and active status is true.

MongoDB

db.collection('users').deleteOne({ firstName: [1], lastName: [2], active: [3] })

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

A'John'

B'Doe'

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around boolean values

Forgetting quotes around string values

String values like 'John' and 'Doe' need quotes. Boolean values like true are unquoted keywords.

Practice

1. What does the deleteOne method do in MongoDB?

easy

A. Deletes all documents in a collection.

B. Updates a single document in the collection.

C. Deletes a single document that matches the filter criteria.

D. Finds a document without deleting it.

Solution

1. Step 1: Understand the purpose of deleteOne

   The deleteOne method is designed to remove exactly one document that matches the given filter.

2. Step 2: Compare with other methods

   Unlike deleteMany, which removes multiple documents, deleteOne targets only one document.

3. Final Answer:

   Deletes a single document that matches the filter criteria. -> Option C

4. Quick Check:

   deleteOne removes one matching document [OK]

Hint: Remember: deleteOne removes only one matching document [OK]

Common Mistakes:

• Confusing deleteOne with deleteMany
• Thinking deleteOne updates documents
• Assuming deleteOne deletes all documents

2. Which of the following is the correct syntax to delete one document where the field name equals "Alice"?

easy

A. db.collection.deleteOne({name: "Alice"})

B. db.collection.deleteOne(name = "Alice")

C. db.collection.deleteOne("name: Alice")

D. db.collection.deleteOne({"name" == "Alice"})

Solution

1. Step 1: Check the filter format

   The filter must be an object with key-value pairs, like {name: "Alice"}.

2. Step 2: Validate method call syntax

   The correct syntax is db.collection.deleteOne(filter) where filter is an object.

3. Final Answer:

   db.collection.deleteOne({name: "Alice"}) -> Option A

4. Quick Check:

   Filter is an object with field and value [OK]

Hint: Use object syntax {field: value} inside deleteOne() [OK]

Common Mistakes:

• Using assignment (=) inside filter
• Passing filter as a string
• Using comparison operators (==) inside filter object

3. Given the collection documents: [{"_id":1, "name":"Bob"}, {"_id":2, "name":"Alice"}, {"_id":3, "name":"Bob"}], what will be the result of db.collection.deleteOne({name: "Bob"})?

medium

A. Deletes the first document with name 'Bob' only.

B. No documents are deleted.

C. Deletes the document with name 'Alice'.

D. Deletes both documents with name 'Bob'.

Solution

1. Step 1: Understand deleteOne behavior

   deleteOne removes only one document matching the filter, not all.

2. Step 2: Identify which document is deleted

   It deletes the first document it finds with name: "Bob", which is the one with _id:1.

3. Final Answer:

   Deletes the first document with name 'Bob' only. -> Option A

4. Quick Check:

   deleteOne removes one matching document, not all [OK]

Hint: deleteOne deletes only one matching document, not all [OK]

Common Mistakes:

• Assuming deleteOne deletes all matches
• Thinking it deletes documents with other names
• Believing no document is deleted if multiple matches exist

4. What is wrong with this code snippet?
db.collection.deleteOne({name: 'John')

medium

A. deleteOne cannot delete documents with name field.

B. Using single quotes instead of double quotes.

C. The method name should be deleteMany.

D. Missing closing brace '}' in the filter object.

Solution

1. Step 1: Check the filter object syntax

   The filter object starts with '{' but does not have a matching closing '}'.

2. Step 2: Validate quotes and method usage

   Single quotes are allowed in JavaScript, and deleteOne is correct for deleting one document.

3. Final Answer:

   Missing closing brace '}' in the filter object. -> Option D

4. Quick Check:

   Filter objects must have matching braces [OK]

Hint: Check for matching braces in filter objects [OK]

Common Mistakes:

• Ignoring missing braces causing syntax errors
• Confusing single vs double quotes as error
• Thinking deleteOne is wrong method here

5. You want to delete a user document only if the user's status is "inactive" and age is greater than 30. Which deleteOne filter correctly achieves this?

hard

A. db.collection.deleteOne({$or: [{status: "inactive"}, {age: {$gt: 30}}]})

B. db.collection.deleteOne({status: "inactive", age: {$gt: 30}})

C. db.collection.deleteOne({status == "inactive", age > 30})

D. db.collection.deleteOne({status: "inactive" || age > 30})

Solution

1. Step 1: Understand filter conditions

   We want to delete a document where both conditions are true: status is "inactive" AND age is greater than 30.

2. Step 2: Check filter syntax for AND condition

   In MongoDB filters, multiple key-value pairs in the object imply logical AND. Thus, db.collection.deleteOne({status: "inactive", age: {$gt: 30}}) is correct. $or would match if either condition is true.

3. Final Answer:

   db.collection.deleteOne({status: "inactive", age: {$gt: 30}}) -> Option B

4. Quick Check:

   Multiple fields in filter imply AND [OK]

Hint: Multiple fields in filter object mean AND conditions [OK]

Common Mistakes:

• Using || inside filter object (invalid syntax)
• Using == inside filter object
• Using $or for AND conditions