deleteMany method in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delete all documents where the field "status" is "inactive".

MongoDB

db.collection.deleteMany({ status: [1] })

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

Anull

B"active"

Ctrue

D"inactive"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around string values.

Using deleteOne instead of deleteMany.

The deleteMany method deletes all documents matching the filter. Here, we want to delete documents where status equals "inactive".

2fill in blank

medium

Complete the code to delete all documents where the "age" field is greater than 30.

MongoDB

db.collection.deleteMany({ age: { [1]: 30 } })

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

A$lt

B$eq

C$gt

D$ne

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt which means less than.

Using $eq which means equal.

The $gt operator means "greater than". This filter deletes documents where age is greater than 30.

3fill in blank

hard

Fix the error in the code to delete documents where "score" is less than or equal to 50.

MongoDB

db.collection.deleteMany({ score: { [1]: 50 } })

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

A$lte

B$gte

C$gt

D$eq

Attempts:

3 left

💡 Hint

Common Mistakes

Using $gte which means greater than or equal.

Using $eq which means equal only.

The operator $lte means "less than or equal to". It correctly filters documents with score less than or equal to 50.

4fill in blank

hard

Fill both blanks to delete documents where "category" is "books" and "price" is less than 20.

MongoDB

db.collection.deleteMany({ category: [1], price: { [2]: 20 } })

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

A"books"

B"electronics"

C$lt

D$gt

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong category string.

Using $gt instead of $lt.

The filter deletes documents with category equal to "books" and price less than 20 using $lt.

5fill in blank

hard

Fill all three blanks to delete documents where "status" is "pending", "priority" is greater than 3, and "assigned" is false.

MongoDB

db.collection.deleteMany({ status: [1], priority: { [2]: 3 }, assigned: [3] })

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

A"pending"

B$gt

Cfalse

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using true instead of false for assigned.

Forgetting quotes around "pending".

Using wrong operator for priority.

This filter deletes documents where status is "pending", priority is greater than 3 using $gt, and assigned is false.

Practice

1. What does the deleteMany method do in MongoDB?

easy

A. Inserts multiple documents into a collection.

B. Deletes only one document regardless of the filter.

C. Removes all documents that match a given filter.

D. Updates multiple documents based on a filter.

Solution

1. Step 1: Understand the purpose of deleteMany

   The deleteMany method is designed to remove multiple documents that match a specified filter in a collection.

2. Step 2: Compare with other methods

   Unlike deleteOne which deletes a single document, deleteMany deletes all matching documents. It does not update or insert documents.

3. Final Answer:

   Removes all documents that match a given filter. -> Option C

4. Quick Check:

   deleteMany removes multiple matching documents = D [OK]

Hint: deleteMany deletes all matching documents, not just one [OK]

Common Mistakes:

• Confusing deleteMany with deleteOne
• Thinking deleteMany updates documents
• Assuming deleteMany inserts documents

2. Which of the following is the correct syntax to delete all documents where status is "inactive" using deleteMany?

easy

A. db.collection.deleteMany({status: "inactive"})

B. db.collection.deleteMany("status = 'inactive'")

C. db.collection.deleteMany(status == "inactive")

D. db.collection.deleteMany([status: "inactive"])

Solution

1. Step 1: Identify correct filter syntax

   The filter in deleteMany must be a JSON object with key-value pairs, like {status: "inactive"}.

2. Step 2: Check each option

   db.collection.deleteMany({status: "inactive"}) uses correct JSON object syntax. Options B, C, and D use invalid syntax for MongoDB filters.

3. Final Answer:

   db.collection.deleteMany({status: "inactive"}) -> Option A

4. Quick Check:

   Filter must be JSON object = A [OK]

Hint: Use JSON object for filter in deleteMany [OK]

Common Mistakes:

• Using string instead of object for filter
• Using comparison operators inside filter incorrectly
• Using array syntax for filter

3. Given the collection users with documents:

{"name": "Alice", "age": 25}, {"name": "Bob", "age": 30}, {"name": "Carol", "age": 25}

What will be the result of db.users.deleteMany({age: 25})?

medium

A. Deletes 2 documents where age is 25

B. Deletes 1 document where age is 25

C. Deletes all documents regardless of age

D. No documents deleted

Solution

1. Step 1: Identify matching documents

   Documents with age: 25 are Alice and Carol, so 2 documents match the filter.

2. Step 2: Understand deleteMany behavior

   deleteMany removes all documents matching the filter, so both Alice and Carol will be deleted.

3. Final Answer:

   Deletes 2 documents where age is 25 -> Option A

4. Quick Check:

   deleteMany removes all matching documents = A [OK]

Hint: deleteMany removes all matching, not just one [OK]

Common Mistakes:

• Thinking only one document is deleted
• Assuming deleteMany deletes all documents
• Confusing filter criteria

4. What is wrong with this code snippet?

db.products.deleteMany("{category: 'electronics'}")

medium

A. deleteMany cannot delete documents by category.

B. The collection name is incorrect.

C. Missing semicolon at the end.

D. Filter should be an object, not a string.

Solution

1. Step 1: Check filter argument type

   The filter argument must be a JSON object, but here it is passed as a string.

2. Step 2: Validate other parts

   deleteMany can delete by any filter, semicolon is optional in JS, and collection name is valid.

3. Final Answer:

   Filter should be an object, not a string. -> Option D

4. Quick Check:

   Filter must be object, not string = B [OK]

Hint: Pass filter as object, not string, in deleteMany [OK]

Common Mistakes:

• Passing filter as string instead of object
• Assuming semicolon is mandatory
• Misnaming collection

5. You want to delete all documents from the orders collection where the status is either "cancelled" or "returned". Which deleteMany filter correctly achieves this?

hard

A. db.orders.deleteMany({status: "cancelled" || "returned"})

B. db.orders.deleteMany({status: {$in: ["cancelled", "returned"]}})

C. db.orders.deleteMany({status: {$or: ["cancelled", "returned"]}})

D. db.orders.deleteMany({status: ["cancelled", "returned"]})

Solution

1. Step 1: Understand filter for multiple values

   To match documents where a field equals any value in a list, MongoDB uses the $in operator with an array of values.

2. Step 2: Evaluate each option

   db.orders.deleteMany({status: {$in: ["cancelled", "returned"]}}) correctly uses $in. db.orders.deleteMany({status: "cancelled" || "returned"}) uses JavaScript OR incorrectly inside an object. db.orders.deleteMany({status: {$or: ["cancelled", "returned"]}}) misuses $or inside a field. db.orders.deleteMany({status: ["cancelled", "returned"]}) uses an array directly, which is invalid.

3. Final Answer:

   db.orders.deleteMany({status: {$in: ["cancelled", "returned"]}}) -> Option B

4. Quick Check:

   Use $in for multiple values in filter = C [OK]

Hint: Use $in operator to match multiple values in deleteMany filter [OK]

Common Mistakes:

• Using JavaScript OR inside filter object
• Misusing $or inside a field filter
• Passing array directly as field value