updateOne method in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update one document in the collection.

MongoDB

db.collection.updateOne({ name: "John" }, { [1]: { age: 30 } })

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

A$unset

B$set

C$inc

D$push

Attempts:

3 left

💡 Hint

Common Mistakes

Using $push instead of $set will try to add to an array, not update a field.

Using $inc will increment a number, not set it to a specific value.

The $set operator updates the value of a field in the matched document.

2fill in blank

medium

Complete the code to update the first document where age is 25.

MongoDB

db.users.updateOne({ age: [1] }, { $set: { status: "active" } })

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

A"25"

Btrue

C25

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string "25" instead of number 25 causes no match.

Using true or null does not match the age field.

The query filter should match the number 25, not the string "25".

3fill in blank

hard

Fix the error in the updateOne call to increment the score by 5.

MongoDB

db.scores.updateOne({ player: "Alice" }, { [1]: { score: 5 } })

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

A$inc

B$set

C$push

D$mul

Attempts:

3 left

💡 Hint

Common Mistakes

Using $set replaces the score instead of incrementing it.

Using $push is for arrays, not numbers.

The $inc operator increments a numeric field by the given value.

4fill in blank

hard

Fill both blanks to update the city and add a new field country.

MongoDB

db.customers.updateOne({ name: "Bob" }, { [1]: { city: "Paris" }, [2]: { country: "France" } })

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

A$set

B$inc

C$unset

D$push

Attempts:

3 left

💡 Hint

Common Mistakes

Using $inc or $unset will not add or update string fields.

Using different operators for each field is incorrect here.

Use $set to update or add fields in the document.

5fill in blank

hard

Fill all three blanks to update the user's email, increment login count, and remove the temp field.

MongoDB

db.users.updateOne({ username: "jane" }, { [1]: { email: "[e-mail]" }, [2]: { logins: 1 }, [3]: { temp: "" } })

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

A$set

B$inc

C$unset

D$push

Attempts:

3 left

💡 Hint

Common Mistakes

Using $push instead of $inc for numbers.

Using $set to remove fields instead of $unset.

Not passing the field name as a string to $unset.

$set updates the email, $inc increments the login count, and $unset removes the temp field.

Practice

1. What does the updateOne method do in MongoDB?

easy

A. Inserts a new document without checking existing ones.

B. Deletes all documents matching the filter.

C. Returns all documents without any update.

D. Updates a single document that matches the filter criteria.

Solution

1. Step 1: Understand the purpose of updateOne

   The updateOne method is designed to update only one document that matches the given filter.

2. Step 2: Compare with other operations

   Deleting or inserting documents are different operations; updateOne specifically updates one matching document.

3. Final Answer:

   Updates a single document that matches the filter criteria. -> Option D

4. Quick Check:

   updateOne updates one document [OK]

Hint: Remember: updateOne changes only one matching document [OK]

Common Mistakes:

• Thinking updateOne deletes documents
• Confusing updateOne with insert operations
• Assuming updateOne updates multiple documents

2. Which of the following is the correct syntax to update the field age to 30 using updateOne?

easy

A. db.collection.updateOne({name: 'John'}, {$change: {age: 30}});

B. db.collection.updateOne({name: 'John'}, {$set: {age: 30}});

C. db.collection.updateOne({name: 'John'}, {$update: {age: 30}});

D. db.collection.updateOne({name: 'John'}, {age: 30});

Solution

1. Step 1: Identify the update operator

   MongoDB requires using $set to update fields safely without replacing the whole document.

2. Step 2: Check syntax correctness

   db.collection.updateOne({name: 'John'}, {$set: {age: 30}}); uses $set correctly; other options use invalid operators or omit $set.

3. Final Answer:

   db.collection.updateOne({name: 'John'}, {$set: {age: 30}}); -> Option B

4. Quick Check:

   Use $set to update fields [OK]

Hint: Always use $set inside updateOne to change fields [OK]

Common Mistakes:

• Omitting $set and passing fields directly
• Using wrong update operators like $update or $change
• Forgetting to wrap update fields in an object

3. Given the collection documents:
{ _id: 1, name: 'Alice', age: 25 }
{ _id: 2, name: 'Bob', age: 28 }
What will be the result of this operation?
db.collection.updateOne({name: 'Alice'}, {$set: {age: 26}});
Then querying db.collection.find({name: 'Alice'})?

medium

A. [{ _id: 1, name: 'Alice', age: 26 }]

B. [{ _id: 1, name: 'Alice', age: 25 }]

C. No documents found

D. [{ _id: 2, name: 'Bob', age: 28 }]

Solution

1. Step 1: Understand updateOne effect

   The updateOne matches the document with name: 'Alice' and updates the age to 26.

2. Step 2: Query after update

   Querying for name: 'Alice' returns the updated document with age: 26.

3. Final Answer:

   [{ _id: 1, name: 'Alice', age: 26 }] -> Option A

4. Quick Check:

   updateOne changes age to 26 [OK]

Hint: updateOne changes one matching document's fields [OK]

Common Mistakes:

• Expecting no change after updateOne
• Confusing which document is updated
• Assuming updateOne updates multiple documents

4. What is wrong with this updateOne command?
db.collection.updateOne({name: 'Eve'}, {age: 35});

medium

A. The collection name is invalid.

B. Filter syntax is incorrect.

C. Missing $set operator to update the field.

D. The updateOne method cannot update numeric fields.

Solution

1. Step 1: Check update document structure

   The update document must use an update operator like $set to modify fields.

2. Step 2: Identify missing operator

   The command directly passes {age: 35} without $set, which replaces the entire document instead of just updating the age field.

3. Final Answer:

   Missing $set operator to update the field. -> Option C

4. Quick Check:

   Always use $set in updateOne updates [OK]

Hint: Always include $set when updating fields [OK]

Common Mistakes:

• Forgetting $set operator
• Assuming updateOne accepts direct field objects
• Misunderstanding filter vs update parts

5. You want to update the document with username: 'mike' to set active: true. If no such document exists, you want to create it with username: 'mike' and active: true. Which updateOne command achieves this?

hard

A. db.collection.updateOne({username: 'mike'}, {$set: {active: true}}, {upsert: true});

B. db.collection.updateOne({username: 'mike'}, {$set: {active: true}});

C. db.collection.updateOne({username: 'mike'}, {active: true}, {upsert: true});

D. db.collection.updateOne({username: 'mike'}, {$set: {active: true}}, {insertIfNotFound: true});

Solution

1. Step 1: Use upsert option for insert if no match

   The upsert: true option tells MongoDB to insert if no document matches the filter.

2. Step 2: Use $set to update or create fields

   The update uses $set to set active: true. The filter ensures username: 'mike' is matched or inserted.

3. Final Answer:

   db.collection.updateOne({username: 'mike'}, {$set: {active: true}}, {upsert: true}); -> Option A

4. Quick Check:

   upsert true + $set updates or inserts [OK]

Hint: Use upsert: true with $set to update or insert [OK]

Common Mistakes:

• Omitting upsert option
• Passing update fields without $set
• Using wrong option name like insertIfNotFound