Composite index requirements in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a composite index for fields 'age' and 'score'.

Firebase

firestore.indexes().create({fields: [{fieldPath: 'age'}, {fieldPath: '[1]'}]})

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

Alocation

Bname

Cdate

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a field not involved in the composite index like 'name' or 'location'.

The composite index must include both 'age' and 'score' fields to support queries filtering or ordering by these fields.

2fill in blank

medium

Complete the code to specify the direction of the composite index on 'age' as ascending.

Firebase

firestore.indexes().create({fields: [{fieldPath: 'age', [1]: 'ASCENDING'}, {fieldPath: 'score', order: 'DESCENDING'}]})

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

Aorder

Bmode

Csort

Ddirection

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'direction' or 'sort' instead of 'order' causes errors.

The correct property to specify the sort order in Firestore composite indexes is 'order'.

3fill in blank

hard

Fix the error in the composite index definition by completing the missing field name.

Firebase

firestore.indexes().create({fields: [{fieldPath: 'age', order: 'ASCENDING'}, {fieldPath: '[1]', order: 'DESCENDING'}]})

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

Ascore

Bage

Cname

Dtimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Repeating 'age' or using unrelated fields like 'name' or 'timestamp'.

The composite index must include 'score' as the second field to match the query requirements.

4fill in blank

hard

Fill both blanks to create a composite index with 'city' ascending and 'population' descending.

Firebase

firestore.indexes().create({fields: [{fieldPath: '[1]', order: 'ASCENDING'}, {fieldPath: '[2]', order: 'DESCENDING'}]})

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

Acity

Bpopulation

Cage

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the fields or using unrelated fields like 'age' or 'score'.

The composite index must have 'city' with ascending order and 'population' with descending order to support queries filtering or ordering by these fields.

5fill in blank

hard

Fill all three blanks to define a composite index with 'country' ascending, 'state' ascending, and 'city' descending.

Firebase

firestore.indexes().create({fields: [{fieldPath: '[1]', order: 'ASCENDING'}, {fieldPath: '[2]', order: 'ASCENDING'}, {fieldPath: '[3]', order: 'DESCENDING'}]})

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

Acountry

Bstate

Ccity

Dpopulation

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'population' instead of 'city' for the descending field.

This composite index supports queries filtering or ordering by 'country' and 'state' ascending, and 'city' descending.

Practice

1. What is the main reason Firebase requires a composite index?

easy

A. To encrypt data for security

B. To store data in multiple locations

C. To backup data automatically

D. To efficiently query data using multiple fields together

Solution

1. Step 1: Understand composite index purpose

   Composite indexes allow Firebase to quickly search using more than one field at the same time.

2. Step 2: Compare options to purpose

   Only To efficiently query data using multiple fields together matches this purpose; others describe unrelated features.

3. Final Answer:

   To efficiently query data using multiple fields together -> Option D

4. Quick Check:

   Composite index = multi-field query speed [OK]

Hint: Composite indexes speed up queries with multiple fields [OK]

Common Mistakes:

• Confusing composite indexes with data backup
• Thinking composite indexes encrypt data
• Believing composite indexes store data in multiple places

2. Which of the following is the correct way to define a composite index in Firebase JSON?

easy

A. "indexes": [{"collectionGroup": "users", "queryScope": "COLLECTION", "fields": [{"fieldPath": "age", "order": "ASCENDING"}, {"fieldPath": "name", "order": "DESCENDING"}]}]

B. "indexes": [{"collection": "users", "fields": ["age", "name"]}]

C. "indexes": [{"collectionGroup": "users", "fields": [{"fieldPath": "age"}, {"fieldPath": "name"}]}]

D. "indexes": [{"collectionGroup": "users", "queryScope": "COLLECTION", "fields": ["age", "name"]}]

Solution

1. Step 1: Check JSON structure for composite index

   Correct composite index JSON includes collectionGroup, queryScope, and fields with fieldPath and order.

2. Step 2: Validate each option

   Only "indexes": [{"collectionGroup": "users", "queryScope": "COLLECTION", "fields": [{"fieldPath": "age", "order": "ASCENDING"}, {"fieldPath": "name", "order": "DESCENDING"}]}] has all required keys and correct field definitions with order specified.

3. Final Answer:

   "indexes": [{"collectionGroup": "users", "queryScope": "COLLECTION", "fields": [{"fieldPath": "age", "order": "ASCENDING"}, {"fieldPath": "name", "order": "DESCENDING"}]}] -> Option A

4. Quick Check:

   Composite index JSON needs fields with order [OK]

Hint: Composite index JSON needs fields with order and collectionGroup [OK]

Common Mistakes:

• Omitting order in fields
• Using 'collection' instead of 'collectionGroup'
• Listing fields as simple strings without objects

3. Given this query in Firebase: db.collection('products').where('category', '==', 'books').orderBy('price', 'asc').orderBy('rating', 'desc'), what composite index is required?

medium

A. Index on fields: category (DESC), price (ASC), rating (ASC)

B. Index on fields: price (ASC), rating (DESC)

C. Index on fields: category (ASC), price (ASC), rating (DESC)

D. No composite index needed

Solution

1. Step 1: Identify query filters and orderBy fields

   The query filters on 'category' and orders by 'price' ascending and 'rating' descending.

2. Step 2: Determine composite index fields and order

   Composite index must include 'category' (filter), then 'price' (asc), then 'rating' (desc) in that order.

3. Final Answer:

   Index on fields: category (ASC), price (ASC), rating (DESC) -> Option C

4. Quick Check:

   Filter + orderBy fields = composite index fields [OK]

Hint: Include all filter and orderBy fields with correct order [OK]

Common Mistakes:

• Ignoring filter field in index
• Wrong order or direction of fields
• Assuming no index needed for multiple orderBy

4. You get an error saying a composite index is missing for this query: db.collection('orders').where('status', '==', 'shipped').orderBy('date', 'desc'). Which fix is correct?

medium

A. Create a composite index on fields: status (ASC), date (DESC)

B. Create a composite index on fields: date (DESC), status (ASC)

C. Create a single-field index on date only

D. No index needed; fix query syntax

Solution

1. Step 1: Analyze query filter and orderBy

   The query filters on 'status' and orders by 'date' descending.

2. Step 2: Determine correct composite index order

   Composite index must start with filter field 'status' (ASC by default), then 'date' (DESC) as orderBy.

3. Final Answer:

   Create a composite index on fields: status (ASC), date (DESC) -> Option A

4. Quick Check:

   Filter field first, then orderBy fields in index [OK]

Hint: Filter field first in index, then orderBy fields [OK]

Common Mistakes:

• Reversing field order in index
• Creating single-field index only
• Ignoring error and changing query syntax

5. You want to query a collection 'events' filtering by 'location' and 'type', and sorting by 'date' ascending. Which composite index definition is correct?

hard

A. Index on fields: date (ASC), location (ASC), type (ASC)

B. Index on fields: location (ASC), type (ASC), date (ASC)

C. Index on fields: location (DESC), type (DESC), date (ASC)

D. No composite index needed if only filtering

Solution

1. Step 1: Identify query filter and sort fields

   The query filters on 'location' and 'type', and sorts by 'date' ascending.

2. Step 2: Determine composite index order

   Composite index must list filter fields first in any order, then the sort field last with ascending order.

3. Step 3: Validate options

   Index on fields: location (ASC), type (ASC), date (ASC) matches filter fields first (location, type) then date ascending. Index on fields: date (ASC), location (ASC), type (ASC) starts with date, which is incorrect. Index on fields: location (DESC), type (DESC), date (ASC) uses descending for filters, which is wrong. No composite index needed if only filtering is incorrect because sorting requires composite index.

4. Final Answer:

   Index on fields: location (ASC), type (ASC), date (ASC) -> Option B

5. Quick Check:

   Filters first, then sort field in index [OK]

Hint: Filter fields first, then sort field ascending in index [OK]

Common Mistakes:

• Placing sort field before filters in index
• Using descending order for filter fields
• Assuming no index needed when sorting