In and not-in queries in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to query documents where the field 'status' is in a list of values.

Firebase

db.collection('orders').where('status', '[1]', ['pending', 'shipped']).get()

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

Anot-in

Bin

C==

Darray-contains

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'array-contains' which checks if an array field contains a value, not if a field matches any value in a list.

Using '==' which only checks for equality with a single value.

The 'in' operator allows querying documents where the field matches any value in the given list.

2fill in blank

medium

Complete the code to query documents where the field 'category' is not in a list of values.

Firebase

db.collection('products').where('category', '[1]', ['electronics', 'furniture']).get()

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

A!=

Barray-contains-any

Cin

Dnot-in

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' which only compares to a single value, not a list.

Using 'in' which includes documents with matching values instead of excluding them.

The 'not-in' operator filters documents where the field's value is not in the specified list.

3fill in blank

hard

Fix the error in the query to find documents where 'tags' array contains any of the given values.

Firebase

db.collection('posts').where('tags', '[1]', ['news', 'updates']).get()

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

Aarray-contains-any

Bin

Carray-contains

Dnot-in

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'in' which checks a field's value against a list, not array contents.

Using 'array-contains' which only checks for a single value.

'array-contains-any' checks if the array field contains any of the specified values.

4fill in blank

hard

Fill both blanks to query documents where 'status' is in a list and 'priority' is not in another list.

Firebase

db.collection('tasks').where('status', '[1]', ['open', 'in-progress']).where('priority', '[2]', ['low', 'medium']).get()

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

Ain

Barray-contains

Cnot-in

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which only compares single values.

Mixing up 'in' and 'not-in' operators.

Use 'in' to include documents with matching 'status' values and 'not-in' to exclude documents with certain 'priority' values.

5fill in blank

hard

Fill all three blanks to query documents where 'category' is in a list, 'tags' array contains any value from a list, and 'status' is not in another list.

Firebase

db.collection('items').where('category', '[1]', ['books', 'games']).where('tags', '[2]', ['bestseller', 'new']).where('status', '[3]', ['archived', 'deleted']).get()

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

Ain

Barray-contains-any

Cnot-in

Darray-contains

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'array-contains' instead of 'array-contains-any' for multiple values.

Using 'in' instead of 'not-in' to exclude values.

Use 'in' for matching 'category', 'array-contains-any' for matching any tag, and 'not-in' to exclude certain statuses.

Practice

1.

What does the in query do in Firebase Firestore?

easy

A. Finds documents where a field is null

B. Finds documents where a field does not exist

C. Finds documents where a field matches exactly one value only

D. Finds documents where a field matches any value in a given list

Solution

1. Step 1: Understand the purpose of in query

   The in query checks if a field's value matches any value from a list of values.

2. Step 2: Compare with other options

   Null fields and non-existent fields describe different query types, while limiting to exactly one value is incorrect for in.

3. Final Answer:

   Finds documents where a field matches any value in a given list -> Option D

4. Quick Check:

   in query = matches any value in list [OK]

Hint: Remember: 'in' means match any value from a list [OK]

Common Mistakes:

• Confusing 'in' with 'not-in' query
• Thinking 'in' matches only one value
• Assuming 'in' checks for field existence

2.

Which of the following is the correct syntax for a not-in query in Firestore?

db.collection('users').where('age', ___, [18, 21, 25])

easy

A. 'notin'

B. 'not-in'

C. 'not_in'

D. 'nin'

Solution

1. Step 1: Recall Firestore query operators

   Firestore uses exact strings for operators; the correct operator for excluding values is 'not-in'.

2. Step 2: Check each option's validity

   'notin', 'not_in', and 'nin' are invalid syntax and will cause errors.

3. Final Answer:

   'not-in' -> Option B

4. Quick Check:

   Correct operator syntax = 'not-in' [OK]

Hint: Use exact operator strings: 'not-in' with hyphen [OK]

Common Mistakes:

• Using 'notin' or 'not_in' instead of 'not-in'
• Missing quotes around operator
• Using unsupported operators like 'nin'

3.

Given this Firestore query:

db.collection('products').where('category', 'in', ['books', 'games']).get()

Which documents will be returned?

medium

A. Documents where category is either 'books' or 'games'

B. Documents where category is not 'books' or 'games'

C. Documents where category is exactly 'booksgames'

D. All documents regardless of category

Solution

1. Step 1: Understand the 'in' query behavior

   The query filters documents where the 'category' field matches any value in the list ['books', 'games'].

2. Step 2: Analyze each option

   Documents where category is either 'books' or 'games' matches the query logic. Documents where category is not 'books' or 'games' is the opposite. Documents where category is exactly 'booksgames' is a concatenation, which is incorrect. All documents regardless of category ignores the filter.

3. Final Answer:

   Documents where category is either 'books' or 'games' -> Option A

4. Quick Check:

   'in' query returns matching values in list [OK]

Hint: Think: 'in' means any value inside the list [OK]

Common Mistakes:

• Confusing 'in' with 'not-in'
• Assuming concatenation of list values
• Ignoring the filter and expecting all documents

4.

What is wrong with this Firestore query?

db.collection('orders').where('status', 'not-in', ['shipped', 'delivered', 'pending', 'cancelled', 'new', 'processing', 'confirmed', 'refunded', 'returned', 'failed', 'on_hold']).get()

It throws an error. Why?

medium

A. The 'not-in' operator cannot be used with more than 10 values in the list

B. The field 'status' does not exist in the collection

C. The 'not-in' operator is not supported in Firestore

D. The list has more than 20 values, exceeding Firestore limits

Solution

1. Step 1: Recall Firestore limits on 'not-in' queries

   Firestore limits 'not-in' and 'in' queries to a maximum of 10 values in the list.

2. Step 2: Count values in the list

   The list has 11 values, exceeding the 10-value limit for 'not-in' queries.

3. Step 3: Consider other options

   The list has more than 20 values, exceeding Firestore limits is incorrect because the list has 11 values. The 'not-in' operator is not supported in Firestore is wrong because 'not-in' is supported. The field 'status' does not exist in the collection is unrelated to the error.

4. Final Answer:

   The 'not-in' operator cannot be used with more than 10 values in the list -> Option A

5. Quick Check:

   'not-in' max 10 values limit causes errors [OK]

Hint: Check list size: 'not-in' max 10 values allowed [OK]

Common Mistakes:

• Assuming 'not-in' supports unlimited list size
• Blaming field existence without checking
• Confusing 'not-in' support in Firestore

5.

You want to find all users whose role is neither 'admin' nor 'moderator' nor 'guest'. Which Firestore query is correct?

hard

A. db.collection('users').where('role', '!=', ['admin', 'moderator', 'guest']).get()

B. db.collection('users').where('role', 'in', ['admin', 'moderator', 'guest']).get()

C. db.collection('users').where('role', 'not-in', ['admin', 'moderator', 'guest']).get()

D. db.collection('users').where('role', 'not-in', 'admin,moderator,guest').get()

Solution

1. Step 1: Understand the requirement

   You want users whose role is NOT any of the listed roles. This means excluding those roles.

2. Step 2: Choose the correct operator and syntax

   The 'not-in' operator excludes documents with any value in the list. db.collection('users').where('role', 'not-in', ['admin', 'moderator', 'guest']).get() uses correct syntax with a list. db.collection('users').where('role', 'in', ['admin', 'moderator', 'guest']).get() includes only those roles, which is opposite. db.collection('users').where('role', '!=', ['admin', 'moderator', 'guest']).get() uses '!=' which does not accept lists. db.collection('users').where('role', 'not-in', 'admin,moderator,guest').get() uses a string instead of a list, which is invalid.

3. Final Answer:

   db.collection('users').where('role', 'not-in', ['admin', 'moderator', 'guest']).get() -> Option C

4. Quick Check:

   Use 'not-in' with list to exclude multiple values [OK]

Hint: Use 'not-in' with array to exclude multiple values [OK]

Common Mistakes:

• Using '!=' with a list instead of a single value
• Passing a string instead of an array for 'not-in'
• Using 'in' instead of 'not-in' for exclusion