Subscription filtering in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to subscribe to new messages with a filter on the channel ID.

GraphQL

subscription OnMessageAdded {
  messageAdded(channelId: [1]) {
    id
    content
  }
}

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

AchannelId

B123

C"123"

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number without quotes for channelId.

Using a variable name instead of a string literal.

The channelId argument must be a string, so it needs quotes around the ID value.

2fill in blank

medium

Complete the filter argument to subscribe only to messages where the author is 'alice'.

GraphQL

subscription OnMessageAdded {
  messageAdded(filter: { author: { [1]: "alice" } }) {
    id
    content
  }
}

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

Aeq

Bneq

Ccontains

Din

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'neq' instead of 'eq' causes filtering for authors not equal to 'alice'.

Using 'contains' or 'in' when exact match is needed.

The 'eq' operator filters messages where author equals 'alice'.

3fill in blank

hard

Fix the error in the subscription filter to only get messages with content length greater than 100.

GraphQL

subscription OnMessageAdded {
  messageAdded(filter: { content: { length: { [1]: 100 } } }) {
    id
    content
  }
}

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

Alte

Blt

Ceq

Dgt

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'lt' or 'lte' filters for smaller content lengths.

Using 'eq' filters only exact length 100, not greater.

The 'gt' operator means 'greater than', which filters content length over 100.

4fill in blank

hard

Fill both blanks to subscribe to messages where the author is 'bob' and the content contains 'hello'.

GraphQL

subscription OnMessageAdded {
  messageAdded(filter: { author: { [1]: "bob" }, content: { [2]: "hello" } }) {
    id
    content
  }
}

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

Aeq

Bneq

Ccontains

Din

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'neq' for author filters out 'bob' messages.

Using 'eq' for content requires exact match, not substring.

Use 'eq' to match author exactly and 'contains' to check if content includes 'hello'.

5fill in blank

hard

Fill all three blanks to subscribe to messages where the channelId is 'general', the author is not 'eve', and the content length is less than 50.

GraphQL

subscription OnMessageAdded {
  messageAdded(filter: { channelId: [1], author: { [2]: "eve" }, content: { length: { [3]: 50 } } }) {
    id
    content
  }
}

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

A"general"

Bneq

Clt

Deq

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the channelId string.

Using 'eq' instead of 'neq' to exclude author.

Using 'gt' instead of 'lt' for content length.

ChannelId must be the string 'general', author filter uses 'neq' to exclude 'eve', and content length uses 'lt' for less than 50.

Practice

1. What is the main purpose of subscription filtering in GraphQL subscriptions?

easy

A. To batch multiple queries into one request

B. To store data permanently in the database

C. To receive only relevant real-time updates based on specified conditions

D. To convert queries into mutations automatically

Solution

1. Step 1: Understand subscription filtering concept

   Subscription filtering allows clients to specify conditions so they only get updates they care about.

2. Step 2: Compare options with concept

   Only To receive only relevant real-time updates based on specified conditions describes receiving relevant real-time updates, which matches subscription filtering.

3. Final Answer:

   To receive only relevant real-time updates based on specified conditions -> Option C

4. Quick Check:

   Subscription filtering = relevant updates [OK]

Hint: Filtering means getting only updates you want [OK]

Common Mistakes:

• Confusing filtering with data storage
• Thinking filtering batches queries
• Assuming filtering changes query types

2. Which of the following is the correct syntax to add a filter argument to a GraphQL subscription named newMessages that filters by userId?

easy

A. subscription { newMessages(userId: "123") { id content } }

B. subscription { newMessages(filter: { userId: "123" }) { id content } }

C. subscription { newMessages(where: userId = "123") { id content } }

D. subscription { newMessages(user_id: "123") { id content } }

Solution

1. Step 1: Identify correct filter argument syntax

   GraphQL subscriptions commonly use a filter argument with an object specifying conditions.

2. Step 2: Match options to syntax

   subscription { newMessages(filter: { userId: "123" }) { id content } } uses filter: { userId: "123" }, which is the correct way to pass filter conditions.

3. Final Answer:

   subscription { newMessages(filter: { userId: "123" }) { id content } } -> Option B

4. Quick Check:

   Filter argument uses object syntax = subscription { newMessages(filter: { userId: "123" }) { id content } } [OK]

Hint: Use filter: { field: value } for subscription filters [OK]

Common Mistakes:

• Using direct argument instead of filter object
• Incorrect filter keyword like where
• Wrong field name casing or underscores

3. Given this subscription query:

subscription { newOrders(filter: { status: "SHIPPED" }) { id status } }

Which orders will the client receive updates for?

medium

A. All orders regardless of status

B. No orders, because filter syntax is invalid

C. Only orders with status "PENDING"

D. Only orders with status "SHIPPED"

Solution

1. Step 1: Analyze the filter condition

   The filter specifies status: "SHIPPED", so only orders with this status qualify.

2. Step 2: Determine which updates are sent

   The subscription sends updates only for orders matching the filter, so only "SHIPPED" orders.

3. Final Answer:

   Only orders with status "SHIPPED" -> Option D

4. Quick Check:

   Filter status = "SHIPPED" means only shipped orders [OK]

Hint: Filter limits updates to matching status only [OK]

Common Mistakes:

• Ignoring filter and expecting all updates
• Confusing status values
• Assuming filter syntax is wrong without checking

4. Consider this subscription query:

subscription { newComments(filter: { postId: 42 }) { id content } }

It returns no updates even when new comments are added to post 42. What is the likely issue?

medium

A. The filter argument is missing the correct type or schema support

B. Subscription queries cannot have filters

C. The filter field name should be post_id instead of postId

D. The subscription name newComments is invalid

Solution

1. Step 1: Check filter usage in subscription

   Filters require the schema to support filtering on the specified field and type.

2. Step 2: Identify why no updates appear

   If the schema does not support filtering by postId, the filter silently blocks updates.

3. Final Answer:

   The filter argument is missing the correct type or schema support -> Option A

4. Quick Check:

   Schema must support filter fields for updates [OK]

Hint: Check schema supports filter fields used [OK]

Common Mistakes:

• Assuming field name casing is always wrong
• Believing filters are not allowed in subscriptions
• Thinking subscription name causes no updates

5. You want to subscribe to real-time updates of tasks but only for tasks assigned to user ID 7 and with priority "HIGH". Which subscription filter is correct?

hard

A. subscription { tasks(filter: { assignedUserId: 7, priority: "HIGH" }) { id title } }

B. subscription { tasks(filter: { assignedUserId: "7", priority: HIGH }) { id title } }

C. subscription { tasks(filter: { assignedUser: 7, priority: "HIGH" }) { id title } }

D. subscription { tasks(filter: { userId: 7, priority: "HIGH" }) { id title } }

Solution

1. Step 1: Match filter fields to requirements

   The filter must use assignedUserId for user ID 7 and priority as "HIGH" string.

2. Step 2: Check option correctness

   subscription { tasks(filter: { assignedUserId: 7, priority: "HIGH" }) { id title } } correctly uses numeric 7 and string "HIGH" with proper field names.

3. Final Answer:

   subscription { tasks(filter: { assignedUserId: 7, priority: "HIGH" }) { id title } } -> Option A

4. Quick Check:

   Correct fields and types in filter = subscription { tasks(filter: { assignedUserId: 7, priority: "HIGH" }) { id title } } [OK]

Hint: Use exact field names and correct value types in filter [OK]

Common Mistakes:

• Using wrong field names like userId instead of assignedUserId
• Mixing string and number types incorrectly
• Omitting quotes around string values