find method basics in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find all documents in the collection.

MongoDB

db.collection.[1]()

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

Ainsert

Bupdate

Cfind

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using insert() instead of find().

Using update() or delete() which modify data.

The find() method retrieves documents from a MongoDB collection.

2fill in blank

medium

Complete the code to find documents where the field 'age' is 25.

MongoDB

db.collection.find([1]: 25})

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

Astatus

Bage

Cscore

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong field name in the query.

Not using an object inside find().

To filter documents by age, use {age: 25} inside find().

3fill in blank

hard

Fix the error in the code to find documents with 'status' equal to 'active'.

MongoDB

db.collection.find({status: [1])

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

A'active'

Bactive"

Cactive

D"active"

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting string values.

Using mismatched or missing quotes.

String values in MongoDB queries must be quoted with double or single quotes. Here, double quotes are correct.

4fill in blank

hard

Fill both blanks to find documents where 'score' is greater than 80.

MongoDB

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

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

A$gt

B$lt

C80

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt which means 'less than'.

Using wrong comparison values.

The operator $gt means 'greater than'. So {score: {$gt: 80}} finds scores above 80.

5fill in blank

hard

Fill all three blanks to find documents where 'age' is less than 30 and only show the 'name' field.

MongoDB

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

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

Aage

B$lt

C30

D$gt

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong operators like $gt.

Not specifying the projection correctly.

Use {age: {$lt: 30}} to find ages less than 30. The second argument {name: 1} shows only the 'name' field.

Practice

1. What does the find method do in MongoDB?

easy

A. It deletes documents from a collection.

B. It updates documents in a collection.

C. It searches for documents that match a query.

D. It creates a new collection.

Solution

1. Step 1: Understand the purpose of find

   The find method is used to search for documents in a collection that match a given query.

2. Step 2: Compare with other operations

   Deleting, updating, or creating collections are done by other methods like deleteOne, updateOne, or createCollection.

3. Final Answer:

   It searches for documents that match a query. -> Option C

4. Quick Check:

   find = search documents [OK]

Hint: Remember: find means search for matching documents [OK]

Common Mistakes:

• Confusing find with delete or update methods
• Thinking find creates collections
• Assuming find modifies documents

2. Which of the following is the correct syntax to find all documents in a collection named users?

easy

A. db.users.find({})

B. db.users.findAll()

C. db.users.search({})

D. db.users.get()

Solution

1. Step 1: Recall the correct method name and syntax

   The correct method to find documents is find, and to find all documents, we pass an empty query {}.

2. Step 2: Check other options for validity

   findAll, search, and get are not valid MongoDB methods.

3. Final Answer:

   db.users.find({}) -> Option A

4. Quick Check:

   Use find({}) to get all documents [OK]

Hint: Use empty braces {} inside find() to get all documents [OK]

Common Mistakes:

• Using non-existent methods like findAll or search
• Omitting parentheses after find
• Passing wrong arguments to find

3. Given the collection products with documents:
{ name: "Pen", price: 5 }
{ name: "Book", price: 15 }
What will db.products.find({ price: { $lt: 10 } }).toArray() return?

medium

A. [{ name: "Pen", price: 5 }]

B. [{ name: "Book", price: 15 }]

C. []

D. [{ name: "Pen", price: 5 }, { name: "Book", price: 15 }]

Solution

1. Step 1: Understand the query filter

   The query { price: { $lt: 10 } } means find documents where price is less than 10.

2. Step 2: Check documents against the filter

   "Pen" has price 5 which is less than 10, "Book" has price 15 which is not less than 10.

3. Final Answer:

   [{ name: "Pen", price: 5 }] -> Option A

4. Quick Check:

   Price < 10 returns only Pen [OK]

Hint: Use $lt to filter values less than a number [OK]

Common Mistakes:

• Confusing $lt with $gt
• Expecting all documents to return
• Not converting cursor to array before viewing

4. What is wrong with this query?
db.orders.find(price: 100)

medium

A. The query should use double quotes around price.

B. The collection name is incorrect.

C. The find method cannot filter by price.

D. Missing curly braces around the query object.

Solution

1. Step 1: Check the syntax of the find method

   The query argument to find must be an object enclosed in curly braces {}.

2. Step 2: Identify the missing braces

   The query is written as price: 100 without braces, which is invalid syntax.

3. Final Answer:

   Missing curly braces around the query object. -> Option D

4. Quick Check:

   Query must be inside {} in find() [OK]

Hint: Always wrap query in curly braces {} inside find() [OK]

Common Mistakes:

• Omitting curly braces around query
• Using wrong collection name
• Thinking quotes are mandatory around keys

5. You want to find all documents in employees collection but only show their name and department fields. Which query is correct?

hard

A. db.employees.find({ name: 1, department: 1 })

B. db.employees.find({}, { name: 1, department: 1, _id: 0 })

C. db.employees.find({}, { name: 1, department: 1 })

D. db.employees.find({ name: 1, department: 1, _id: 0 })

Solution

1. Step 1: Understand projection in find()

   Projection is the second argument to find and specifies which fields to include (1) or exclude (0).

2. Step 2: Check the correct syntax for showing only name and department

   Use { name: 1, department: 1, _id: 0 } to include those fields and exclude the _id field.

3. Final Answer:

   db.employees.find({}, { name: 1, department: 1, _id: 0 }) -> Option B

4. Quick Check:

   Projection is second arg with 1 to include fields [OK]

Hint: Use second argument in find() to project fields [OK]

Common Mistakes:

• Putting projection inside the query object
• Not excluding _id when projecting
• Using query to filter fields instead of projection