$all operator for matching all elements in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find documents where the 'tags' array contains all specified elements.

MongoDB

db.collection.find({ tags: { [1]: ["red", "blue"] } })

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

A$in

B$exists

C$elemMatch

D$all

Attempts:

3 left

💡 Hint

Common Mistakes

Using $in instead of $all matches any one element, not all.

Using $elemMatch is for matching elements with conditions, not all elements.

Using $exists checks for field existence, not array contents.

The $all operator matches documents where the array contains all the specified elements.

2fill in blank

medium

Complete the query to find documents where the 'colors' array contains all of 'green' and 'yellow'.

MongoDB

db.products.find({ colors: { [1]: ["green", "yellow"] } })

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

A$elemMatch

B$in

C$all

D$size

Attempts:

3 left

💡 Hint

Common Mistakes

Using $in returns documents with any one of the elements, not all.

Using $size checks array length, not contents.

Using $elemMatch is for matching elements with conditions.

The $all operator ensures the array contains all specified elements.

3fill in blank

hard

Fix the error in the query to correctly find documents where 'features' contains all specified values.

MongoDB

db.items.find({ features: { [1]: ["wifi", "bluetooth"] } })

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

A$all

B$exists

C$elemMatch

D$in

Attempts:

3 left

💡 Hint

Common Mistakes

Using $in matches any element, not all.

Using $elemMatch is for complex conditions, not all elements.

Using $exists checks if the field exists, not its contents.

Only $all matches documents where the array contains all listed elements.

4fill in blank

hard

Fill both blanks to find documents where 'skills' array contains all specified skills and the 'level' is 'advanced'.

MongoDB

db.users.find({ skills: { [1]: ["python", "mongodb"] }, level: [2] })

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

A$all

B"advanced"

C"beginner"

D$in

Attempts:

3 left

💡 Hint

Common Mistakes

Using $in instead of $all for skills.

Using wrong string for level like "beginner".

Not quoting the level string.

Use $all to match all skills and specify the level as the string "advanced".

5fill in blank

hard

Fill all three blanks to find documents where 'tags' contains all specified tags, 'status' is 'active', and 'priority' is greater than 5.

MongoDB

db.tasks.find({ tags: { [1]: ["urgent", "client"] }, status: [2], priority: { [3]: 5 } })

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

A$all

B"active"

C$gt

D$in

Attempts:

3 left

💡 Hint

Common Mistakes

Using $in instead of $all for tags.

Not quoting the status string.

Using $lt or $lte instead of $gt for priority.

Use $all for tags, "active" string for status, and $gt operator for priority greater than 5.

Practice

1.

What does the $all operator do in MongoDB queries?

easy

A. Matches documents where an array contains any one of the specified values.

B. Matches documents where an array contains all specified values.

C. Matches documents where an array contains exactly one specified value.

D. Matches documents where an array is empty.

Solution

1. Step 1: Understand the purpose of $all

   The $all operator is used to find documents where an array field contains all the values specified in the query.

2. Step 2: Compare with other operators

   Unlike $in which matches any value, $all requires all values to be present in the array.

3. Final Answer:

   Matches documents where an array contains all specified values. -> Option B

4. Quick Check:

   $all = all values present [OK]

Hint: Remember: $all means every value must be in the array [OK]

Common Mistakes:

• Confusing $all with $in operator
• Thinking $all checks order of elements
• Assuming $all matches partial values

2.

Which of the following is the correct syntax to find documents where the tags array contains both "red" and "blue" using $all?

{ tags: { $all: ["red", "blue"] } }

easy

A. { tags: { $all: ["red", "blue"] } }

B. { tags: { $all: "red", "blue" } }

C. { tags: { $all: "red blue" } }

D. { tags: { $all: { "red", "blue" } } }

Solution

1. Step 1: Check the correct structure for $all

   The $all operator requires an array of values to match all elements.

2. Step 2: Validate each option's syntax

   { tags: { $all: ["red", "blue"] } } correctly uses an array with square brackets. Options A, B, and D use incorrect syntax for arrays or objects.

3. Final Answer:

   { tags: { $all: ["red", "blue"] } } -> Option A

4. Quick Check:

   Correct array syntax for $all [OK]

Hint: Use square brackets [] to list values inside $all [OK]

Common Mistakes:

• Using curly braces {} instead of square brackets []
• Passing values as separate arguments instead of an array
• Using a string instead of an array for $all

3.

Given the collection documents:

[{ "colors": ["red", "green", "blue"] }, { "colors": ["red", "yellow"] }, { "colors": ["blue", "green", "red"] }]

What will the query { colors: { $all: ["red", "blue"] } } return?

medium

A. No documents

B. Document 2 only

C. Documents 1 and 3

D. All three documents

Solution

1. Step 1: Check each document's colors array

   Document 1 has ["red", "green", "blue"] which includes both "red" and "blue". Document 2 has ["red", "yellow"] missing "blue". Document 3 has ["blue", "green", "red"] which includes both.

2. Step 2: Apply $all condition

   The query matches documents where both "red" and "blue" are present, so documents 1 and 3 match.

3. Final Answer:

   Documents 1 and 3 -> Option C

4. Quick Check:

   Both arrays contain "red" and "blue" [OK]

Hint: Check each array contains all values, order doesn't matter [OK]

Common Mistakes:

• Assuming order matters for $all
• Including documents missing one value
• Confusing $all with $in behavior

4.

Identify the error in this query that tries to find documents where features array contains both "wifi" and "parking":

{ features: { $all: "wifi", "parking" } }

medium

A. The field name should be inside quotes.

B. The values should be inside curly braces instead of quotes.

C. The query should use $in instead of $all.

D. The $all operator requires an array of values, not separate arguments.

Solution

1. Step 1: Analyze the $all operator usage

   The $all operator expects a single array containing all values to match.

2. Step 2: Identify the syntax error

   The query incorrectly passes two separate string arguments instead of an array. It should be { $all: ["wifi", "parking"] }.

3. Final Answer:

   The $all operator requires an array of values, not separate arguments. -> Option D

4. Quick Check:

   $all needs an array [OK]

Hint: Always wrap $all values in an array [] [OK]

Common Mistakes:

• Passing multiple values without array brackets
• Using $in when $all is needed
• Misplacing quotes around field names

5.

You have a collection of documents with a field ingredients which is an array of strings. You want to find all recipes that contain both "flour" and "sugar", but not "nuts". Which query correctly uses $all and other operators to achieve this?

hard

A. { ingredients: { $all: ["flour", "sugar"], $nin: ["nuts"] } }

B. { ingredients: { $all: ["flour", "sugar", "nuts"] } }

C. { ingredients: { $in: ["flour", "sugar"], $nin: ["nuts"] } }

D. { ingredients: { $all: ["flour", "sugar"] }, ingredients: { $nin: ["nuts"] } }

Solution

1. Step 1: Use $all to match both "flour" and "sugar"

   The $all operator ensures the array contains both these ingredients.

2. Step 2: Use $nin to exclude "nuts"

   The $nin operator excludes documents where the array contains "nuts".

3. Step 3: Combine both conditions correctly

   { ingredients: { $all: ["flour", "sugar"], $nin: ["nuts"] } } combines $all and $nin inside the same field query, which is valid MongoDB syntax.

4. Final Answer:

   { ingredients: { $all: ["flour", "sugar"], $nin: ["nuts"] } } -> Option A

5. Quick Check:

   All required and no excluded ingredients [OK]

Hint: Combine $all and $nin inside one field object [OK]

Common Mistakes:

• Putting $all and $nin in separate objects for same field
• Using $in instead of $all for required ingredients
• Including excluded items inside $all array