BSON data types overview in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this BSON document query?

Given a MongoDB collection with documents containing a field value of type Int32, what will be the output of this query?

db.collection.find({ value: { $type: 16 } })

Note: $type: 16 filters documents where value is of BSON type Int32.

MongoDB

db.collection.find({ value: { $type: 16 } })

A Returns documents where 'value' is a 32-bit integer (Int32).

B Returns documents where 'value' is a 64-bit integer (Int64).

C Returns documents where 'value' is a double (floating point).

D Returns documents where 'value' is a string.

💡 Hint

Check the BSON type number for Int32 in MongoDB documentation.

In MongoDB, BSON type 16 corresponds to Int32. The query filters documents where 'value' is exactly a 32-bit integer.

🧠 Conceptual

intermediate

Which BSON data type is used to store date and time?

In BSON, which data type is used to store date and time values?

A Date

B Timestamp

C String

D ObjectId

💡 Hint

Think about the type that stores calendar dates and times.

The BSON 'Date' type stores date and time as milliseconds since the Unix epoch.

📝 Syntax

advanced

Identify the BSON type code for a 64-bit integer

Which BSON type number corresponds to a 64-bit integer (Int64) in MongoDB?

A 16

B 18

C 1

D 2

💡 Hint

Int32 is 16, double is 1, string is 2.

BSON type 18 represents Int64 (64-bit integer).

🔧 Debug

advanced

Why does this query return no results?

A user runs this query to find documents with a field score of type double:

db.collection.find({ score: { $type: 1 } })

But no documents are returned, even though some documents have score as a floating-point number. What is the most likely reason?

A The query syntax is incorrect; $type expects a string, not a number.

B The collection is empty.

C The <code>score</code> field is stored as Int32, not double.

D The <code>score</code> field is stored as string, not double.

💡 Hint

Check the actual BSON type of the score field in documents.

If score is stored as a string, filtering by $type:1 (double) returns no matches.

❓ optimization

expert

Optimizing queries filtering by BSON type

You want to optimize a MongoDB query that filters documents by the BSON type of a field data. Which approach is the most efficient for large collections?

A Use <code>{ data: { $exists: true } }</code> and then check type in application.

B Use <code>{ $where: function() { return typeof this.data === 'number'; } }</code>.

C Use <code>{ data: { $type: <type_number> } }</code> with an index on <code>data</code>.

D Scan all documents and filter in application code after fetching.

💡 Hint

Indexes help queries run faster when used properly.

Using $type with an index on the field allows MongoDB to efficiently filter documents by BSON type.

Practice

1. Which BSON data type is used to store a unique identifier for documents in MongoDB?

easy

A. Date

B. String

C. ObjectId

D. Boolean

Solution

1. Step 1: Understand the purpose of ObjectId

   ObjectId is a special BSON type designed to uniquely identify documents in MongoDB collections.

2. Step 2: Compare with other types

   String stores text, Boolean stores true/false, Date stores time values. None of these uniquely identify documents like ObjectId.

3. Final Answer:

   ObjectId -> Option C

4. Quick Check:

   BSON unique ID = ObjectId [OK]

Hint: Unique document IDs in MongoDB are ObjectIds [OK]

Common Mistakes:

• Confusing String with ObjectId for unique IDs
• Thinking Boolean can identify documents
• Assuming Date stores unique identifiers

2. Which of the following is the correct BSON data type to store a true or false value in MongoDB?

easy

A. Integer

B. Boolean

C. String

D. Array

Solution

1. Step 1: Identify the BSON type for true/false

   Boolean is the BSON data type used to store true or false values.

2. Step 2: Eliminate other types

   Integer stores numbers, String stores text, Array stores lists. None represent true/false directly.

3. Final Answer:

   Boolean -> Option B

4. Quick Check:

   True/false = Boolean [OK]

Hint: True or false values use Boolean type [OK]

Common Mistakes:

• Using Integer for true/false
• Confusing String with Boolean
• Choosing Array for single true/false

3. Given the following MongoDB document:
{ "name": "Alice", "age": 30, "member": true }
What BSON data types are used for the fields name, age, and member respectively?

medium

A. String, Boolean, Integer

B. String, String, Boolean

C. ObjectId, Integer, Boolean

D. String, Integer, Boolean

Solution

1. Step 1: Identify each field's value type

   "name" is text, so String; "age" is a number, so Integer; "member" is true/false, so Boolean.

2. Step 2: Match with options

   String, Integer, Boolean matches String, Integer, Boolean in order. Others mismatch types.

3. Final Answer:

   String, Integer, Boolean -> Option D

4. Quick Check:

   Text, number, true/false = String, Integer, Boolean [OK]

Hint: Match field values to String, Integer, Boolean types [OK]

Common Mistakes:

• Confusing Integer with String for numbers
• Mixing Boolean and Integer types
• Assuming ObjectId for name field

4. You try to insert this document into MongoDB:
{ "date": "2023-01-01" }
But you want the date field to be stored as a BSON Date type. What is the issue and how to fix it?

medium

A. The date is a string; convert it to BSON Date using ISODate()

B. The date is missing; add a date field

C. The date format is invalid; use YYYY/DD/MM instead

D. MongoDB does not support Date type; use String instead

Solution

1. Step 1: Identify the current data type of date field

   The date is stored as a string because it is enclosed in quotes.

2. Step 2: Convert string to BSON Date type

   Use MongoDB's ISODate() function to store the date as BSON Date type.

3. Final Answer:

   The date is a string; convert it to BSON Date using ISODate() -> Option A

4. Quick Check:

   Date string needs ISODate() for BSON Date [OK]

Hint: Use ISODate() to store dates, not strings [OK]

Common Mistakes:

• Assuming string is automatically Date
• Changing date format incorrectly
• Believing MongoDB lacks Date type

5. You want to store a list of tags for a blog post in MongoDB. Which BSON data type should you use to store multiple tag strings together?

hard

A. Array

B. ObjectId

C. Boolean

D. Date

Solution

1. Step 1: Understand the need to store multiple values

   A list of tags means multiple values grouped together.

2. Step 2: Identify BSON type for multiple values

   Array is the BSON type used to store lists or collections of values.

3. Final Answer:

   Array -> Option A

4. Quick Check:

   Multiple values = Array type [OK]

Hint: Use Array type for lists of values [OK]

Common Mistakes:

• Using ObjectId for lists
• Choosing Boolean for multiple tags
• Trying to store list as Date