skip method for offset in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to skip the first 5 documents in the collection.

MongoDB

db.collection.find().[1](5)

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

Alimit

Bskip

Csort

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using limit instead of skip, which restricts the number of documents returned but does not skip.

Using sort or count which do not skip documents.

The skip method is used to skip a number of documents in the result set. Here, skip(5) skips the first 5 documents.

2fill in blank

medium

Complete the code to skip 10 documents and limit the result to 5 documents.

MongoDB

db.collection.find().skip(10).[1](5)

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

Asort

Bcount

Cskip

Dlimit

Attempts:

3 left

💡 Hint

Common Mistakes

Using skip again instead of limit, which would skip more documents instead of limiting.

Using count which returns a number, not documents.

After skipping 10 documents, limit(5) restricts the output to 5 documents.

3fill in blank

hard

Fix the error in the code to skip 3 documents correctly.

MongoDB

db.collection.find().[1](3)

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

Askip[]

Bskip.

Cskip

Dskip()

Attempts:

3 left

💡 Hint

Common Mistakes

Writing skip3 without parentheses causes a syntax error.

Using skip. or skip[] are invalid syntax.

The skip method requires parentheses with the number inside: skip(3).

4fill in blank

hard

Fill both blanks to skip 7 documents and sort by 'age' ascending.

MongoDB

db.collection.find().[1](7).[2]({ age: 1 })

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

Askip

Blimit

Csort

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using limit instead of skip for the first blank.

Using count instead of sort for the second blank.

First, skip(7) skips 7 documents. Then, sort({ age: 1 }) sorts the remaining documents by age in ascending order.

5fill in blank

hard

Fill all three blanks to skip 4 documents, limit to 3 documents, and sort by 'name' descending.

MongoDB

db.collection.find().[1](4).[2](3).[3]({ name: -1 })

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

Askip

Blimit

Csort

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of methods.

Using count instead of sort for sorting.

The methods are chained: skip(4) skips 4 documents, limit(3) limits the result to 3 documents, and sort({ name: -1 }) sorts by name descending.

Practice

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

easy

A. It limits the number of documents returned.

B. It skips a specified number of documents from the start of the result set.

C. It sorts the documents in ascending order.

D. It deletes documents from the collection.

Solution

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

   The skip() method is used to ignore a certain number of documents from the beginning of the query result.

2. Step 2: Differentiate from other methods

   Unlike limit() which restricts the number of documents returned, skip() just moves the starting point forward.

3. Final Answer:

   It skips a specified number of documents from the start of the result set. -> Option B

4. Quick Check:

   skip() = skip documents [OK]

Hint: Remember: skip moves start point, limit controls count [OK]

Common Mistakes:

• Confusing skip with limit
• Thinking skip sorts documents
• Assuming skip deletes documents

2. Which of the following is the correct syntax to skip 5 documents in a MongoDB query on collection users?

easy

A. db.users.find().skip(5)

B. db.users.skip(5).find()

C. db.users.find().limit(5)

D. db.users.find().offset(5)

Solution

1. Step 1: Recall correct method chaining

   In MongoDB, skip() is chained after find() to skip documents.

2. Step 2: Check each option

   db.users.find().skip(5) uses find().skip(5) which is correct syntax. db.users.skip(5).find() incorrectly places skip() before find(). db.users.find().limit(5) uses limit() which limits results, not skips. db.users.find().offset(5) uses offset() which is not a MongoDB method.

3. Final Answer:

   db.users.find().skip(5) -> Option A

4. Quick Check:

   Correct chaining = find().skip() [OK]

Hint: Always chain skip() after find() in MongoDB [OK]

Common Mistakes:

• Using skip() before find()
• Confusing skip() with limit()
• Using offset() which is invalid

3. Given the collection products with documents [{"name": "A"}, {"name": "B"}, {"name": "C"}, {"name": "D"}], what will db.products.find().skip(2).limit(2).toArray() return?

medium

A. [{"name": "A"}, {"name": "B"}]

B. [{"name": "B"}, {"name": "C"}]

C. [{"name": "D"}]

D. [{"name": "C"}, {"name": "D"}]

Solution

1. Step 1: Understand skip and limit effect

   skip(2) ignores the first two documents: "A" and "B". Then limit(2) returns the next two documents.

2. Step 2: Identify returned documents

   After skipping "A" and "B", the next two are "C" and "D". So the result is [{"name": "C"}, {"name": "D"}].

3. Final Answer:

   [{"name": "C"}, {"name": "D"}] -> Option D

4. Quick Check:

   skip 2 + limit 2 = next 2 docs [OK]

Hint: Skip removes first N, limit picks next M [OK]

Common Mistakes:

• Forgetting skip removes documents
• Mixing order of skip and limit
• Assuming skip returns skipped docs

4. You wrote db.orders.skip(3).find() to skip 3 documents but it throws an error. What is the problem?

medium

A. The skip() method must be called after find().

B. The skip() method does not exist in MongoDB.

C. You must use limit() before skip().

D. The number inside skip() must be a string.

Solution

1. Step 1: Check method order in MongoDB queries

   In MongoDB, skip() is a cursor method and must be chained after find(), not before.

2. Step 2: Identify the error cause

   Calling skip() before find() causes a syntax error because skip() is not a collection method.

3. Final Answer:

   The skip() method must be called after find(). -> Option A

4. Quick Check:

   Correct chaining order = find().skip() [OK]

Hint: Always call skip() after find() to avoid errors [OK]

Common Mistakes:

• Calling skip() before find()
• Using string instead of number in skip()
• Thinking skip() requires limit() first

5. You want to display page 3 of a product list with 10 items per page using MongoDB. Which query correctly skips the right number of documents?

hard

A. db.products.find().skip(10).limit(3)

B. db.products.find().skip(30).limit(10)

C. db.products.find().skip(20).limit(10)

D. db.products.find().limit(10).skip(20)

Solution

1. Step 1: Calculate skip value for page 3

   Each page shows 10 items. Page 1 skips 0, page 2 skips 10, so page 3 skips 20 documents (2 pages x 10 items).

2. Step 2: Verify query correctness

   db.products.find().skip(20).limit(10) skips 20 and limits to 10, which is correct. db.products.find().skip(30).limit(10) skips 30 which is too many for page 3. db.products.find().skip(10).limit(3) skips 10 but limits to 3 items, wrong limit. db.products.find().limit(10).skip(20) places limit before skip, which limits to first 10 documents then skips 20 from them (impossible), returning empty.

3. Final Answer:

   db.products.find().skip(20).limit(10) -> Option C

4. Quick Check:

   Page 3 skip = (3-1)*10 = 20 [OK]

Hint: Skip = (page-1)*itemsPerPage, then limit itemsPerPage [OK]

Common Mistakes:

• Calculating skip as page*itemsPerPage
• Swapping skip and limit order
• Using wrong limit count