Excluding fields from results in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to exclude the field 'password' from the query results.

MongoDB

db.users.find({}, { [1]: 0 })

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

Aemail

Bpassword: 1

C_id

Dpassword

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0 to exclude fields.

Excluding the wrong field name.

Setting the field 'password' to 0 in the projection excludes it from the results.

2fill in blank

medium

Complete the code to exclude both 'password' and 'email' fields from the results.

MongoDB

db.users.find({}, { password: 0, [1]: 0 })

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

Ausername

Bemail

C_id

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0 for exclusion.

Forgetting to add the second field.

To exclude multiple fields, set each field to 0 in the projection object.

3fill in blank

hard

Fix the error in the code to exclude the 'password' field correctly.

MongoDB

db.users.find({}, { [1] })

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

Apassword: 1

Bpassword

Cpassword: 0

Dpassword: false

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0 to exclude fields.

Using boolean false instead of 0.

Use 'password: 0' to exclude the field. Using 1 includes it, which is incorrect here.

4fill in blank

hard

Fill both blanks to exclude 'password' and include only 'username' in the results.

MongoDB

db.users.find({}, { [1]: 0, [2]: 1 })

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

Apassword

Busername

Cemail

D_id

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to exclude and include fields incorrectly together.

Using wrong field names.

Set 'password' to 0 to exclude it and 'username' to 1 to include it explicitly.

5fill in blank

hard

Fill all three blanks to exclude 'password' and 'email', and include only 'username' in the results.

MongoDB

db.users.find({}, { [1]: 0, [2]: 0, [3]: 1 })

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

Apassword

Busername

Cemail

D_id

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up which fields to exclude and include.

Using 1 to exclude fields.

Set 'password' and 'email' to 0 to exclude them, and 'username' to 1 to include it.

Practice

1. What does setting a field to 0 in a MongoDB query projection do?

easy

A. It excludes that field from the query results.

B. It includes that field in the query results.

C. It renames the field in the query results.

D. It sorts the results by that field.

Solution

1. Step 1: Understand projection in MongoDB

   Projection controls which fields appear in the query results.

2. Step 2: Interpret setting a field to 0

   Setting a field to 0 means exclude that field from the results.

3. Final Answer:

   It excludes that field from the query results. -> Option A

4. Quick Check:

   Field set to 0 = excluded [OK]

Hint: Use 0 in projection to exclude fields quickly [OK]

Common Mistakes:

• Thinking 0 includes the field
• Confusing exclusion with sorting
• Mixing exclusion and inclusion in projection

2. Which of the following is the correct syntax to exclude the field password from the results in a MongoDB query?

easy

A. db.users.find({}, {password: 0})

B. db.users.find({}, {password: 1})

C. db.users.find({password: 0})

D. db.users.find({}, {exclude: 'password'})

Solution

1. Step 1: Identify correct projection syntax

   Projection is the second argument to find(), with field names and 0 or 1 values.

2. Step 2: Exclude field by setting it to 0

   Setting password: 0 excludes it from results.

3. Final Answer:

   db.users.find({}, {password: 0}) -> Option A

4. Quick Check:

   Exclude field = field: 0 in projection [OK]

Hint: Use {field: 0} in second find() argument to exclude [OK]

Common Mistakes:

• Using 1 instead of 0 to exclude
• Putting projection inside query filter
• Using non-existent 'exclude' keyword

3. Given the collection products with documents like {_id: 1, name: 'Pen', price: 5, stock: 100}, what will be the result of db.products.find({}, {price: 0, stock: 0})?

medium

A. [{name: 'Pen', price: 5, stock: 100}]

B. [{name: 'Pen'}]

C. [{_id: 1, price: 5, stock: 100}]

D. [{_id: 1, name: 'Pen'}]

Solution

1. Step 1: Understand projection excludes price and stock

   Setting price: 0 and stock: 0 excludes these fields from results.

2. Step 2: Check which fields remain

   _id is included by default, name is included as not excluded.

3. Final Answer:

   [{_id: 1, name: 'Pen'}] -> Option D

4. Quick Check:

   Excluded fields missing, others present [OK]

Hint: Excluded fields disappear; others stay including _id by default [OK]

Common Mistakes:

• Expecting excluded fields to appear
• Forgetting _id is included by default
• Assuming all fields are excluded

4. What is wrong with this MongoDB query to exclude email and include name fields: db.users.find({}, {email: 0, name: 1})?

medium

A. You should use exclude keyword instead of 0.

B. The syntax is correct and will work as expected.

C. You cannot mix exclusion and inclusion except for _id.

D. You must exclude _id explicitly when mixing fields.

Solution

1. Step 1: Recall projection rules

   MongoDB does not allow mixing inclusion and exclusion in projection except for _id.

2. Step 2: Analyze the query

   Query mixes email: 0 (exclude) and name: 1 (include), which is invalid.

3. Final Answer:

   You cannot mix exclusion and inclusion except for _id. -> Option C

4. Quick Check:

   Mixing 0 and 1 fields (except _id) = error [OK]

Hint: Exclude or include fields, but don't mix except _id [OK]

Common Mistakes:

• Mixing 0 and 1 in projection
• Assuming syntax is always flexible
• Using 'exclude' keyword which doesn't exist

5. You want to query orders collection and exclude creditCardNumber and cvv fields for security, but include all other fields including _id. Which query achieves this correctly?

hard

A. db.orders.find({}, {creditCardNumber: 1, cvv: 1})

B. db.orders.find({}, {creditCardNumber: 0, cvv: 0})

C. db.orders.find({}, {creditCardNumber: 0, cvv: 0, _id: 0})

D. db.orders.find({}, {creditCardNumber: false, cvv: false})

Solution

1. Step 1: Exclude sensitive fields by setting them to 0

   Setting creditCardNumber and cvv to 0 excludes them from results.

2. Step 2: Keep _id included by default

   Not excluding _id means it stays included, as required.

3. Final Answer:

   db.orders.find({}, {creditCardNumber: 0, cvv: 0}) -> Option B

4. Quick Check:

   Exclude sensitive fields only, keep others including _id [OK]

Hint: Exclude sensitive fields with 0, leave others alone [OK]

Common Mistakes:

• Excluding _id unintentionally
• Using 1 to exclude fields
• Using false instead of 0