Delete mutation pattern in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this delete mutation?

Given the following GraphQL mutation to delete a user by ID, what will be the output if the user with ID 5 exists?

GraphQL

mutation {
  deleteUser(id: 5) {
    id
    name
  }
}

A { "errors": [ { "message": "User not found" } ] }

B { "data": { "deleteUser": null } }

C { "data": { "deleteUser": { "id": 5, "name": "Alice" } } }

D { "data": { "deleteUser": { "id": 6, "name": "Bob" } } }

💡 Hint

Think about what the mutation returns after deleting an existing user.

The delete mutation returns the deleted user's data if the user exists. Since user with ID 5 exists, it returns their id and name.

🧠 Conceptual

intermediate

Which statement about delete mutations is true?

Choose the correct statement about delete mutations in GraphQL.

A Delete mutations always return a boolean indicating success or failure.

B Delete mutations can return the deleted object's data for confirmation.

C Delete mutations cannot accept arguments to specify which record to delete.

D Delete mutations automatically cascade delete related records without configuration.

💡 Hint

Consider what information is useful to return after deleting an item.

Delete mutations often return the deleted object's data so clients can confirm what was deleted. They do not always return just a boolean.

📝 Syntax

advanced

Identify the syntax error in this delete mutation

Which option contains the correct syntax for deleting a post by ID?

GraphQL

mutation {
  deletePost(id: 10) {
    id
    title
  }
}

A

mutation {
  deletePost(id: 10) {
    id
    title
  }
}

B

mutation {
  deletePost(id: "10") {
    id
    title
  }
}

C

mutation {
  deletePost(postId: 10) {
    id
    title
  }
}

D

mutation {
  deletePost {
    id
    title
  }
}

💡 Hint

Check the argument name and type carefully.

Option A uses the correct argument name 'id' with an integer value. Option A uses a string instead of integer. Option A uses wrong argument name 'postId'. Option A omits the required argument.

❓ optimization

advanced

How to optimize a delete mutation for batch deletions?

You want to delete multiple users by their IDs in one mutation call. Which approach is best?

A Create a deleteUsers mutation that accepts a list of IDs and deletes them all.

B Call the deleteUser mutation multiple times, once per ID.

C Use a query to fetch users and then delete them one by one on the client side.

D Delete users by sending a comma-separated string of IDs to deleteUser mutation.

💡 Hint

Think about reducing network calls and improving efficiency.

Batch deleting with a mutation that accepts a list of IDs reduces network overhead and improves performance.

🔧 Debug

expert

Why does this delete mutation return null instead of deleted data?

Given this mutation:

mutation {
  deleteComment(id: 7) {
    id
    content
  }
}

The server returns { "data": { "deleteComment": null } }. What is the most likely reason?

A The client query is missing required fields in the selection set.

B The mutation resolver forgot to return the deleted comment data.

C The server has a syntax error in the deleteComment mutation definition.

D The comment with ID 7 does not exist in the database.

💡 Hint

Consider what happens if the item to delete is not found.

If the item to delete does not exist, the resolver often returns null to indicate nothing was deleted.

Practice

1.

What is the main purpose of a delete mutation in GraphQL?

easy

A. To update existing data in the database

B. To add new data to the database

C. To remove data from the database using an identifier

D. To fetch data without modifying it

Solution

1. Step 1: Understand the role of delete mutations

   Delete mutations are designed to remove data entries, usually by specifying an ID or unique key.

2. Step 2: Compare with other mutation types

   Add mutations create data, update mutations modify data, and queries fetch data without changes.

3. Final Answer:

   To remove data from the database using an identifier -> Option C

4. Quick Check:

   Delete mutation = remove data [OK]

Hint: Delete mutations always remove data by ID [OK]

Common Mistakes:

• Confusing delete with add or update mutations
• Thinking delete fetches data
• Assuming delete mutations do not require an identifier

2.

Which of the following is the correct syntax for a GraphQL delete mutation to remove a user by ID?

mutation {
  deleteUser(id: "123") {
    success
    message
  }
}

easy

A. mutation { deleteUser(id: "123") { success message } }

B. mutation { deleteUser { id: "123" success message } }

C. mutation { deleteUser(id: 123) { success message } }

D. mutation { deleteUser(id: "123") success message }

Solution

1. Step 1: Check argument placement and syntax

   The ID must be passed as an argument inside parentheses with quotes for string: id: "123".

2. Step 2: Verify the selection set braces

   The fields to return (success, message) must be inside braces after the mutation call.

3. Final Answer:

   mutation { deleteUser(id: "123") { success message } } -> Option A

4. Quick Check:

   Correct syntax = mutation { deleteUser(id: "123") { success message } } [OK]

Hint: Arguments go inside parentheses, fields inside braces [OK]

Common Mistakes:

• Passing id without quotes for string
• Placing fields outside braces
• Misplacing argument inside selection set

3.

Given the following delete mutation and response, what is the value of success?

mutation {
  deletePost(id: "abc") {
    success
    message
  }
}

Response:

{
  "data": {
    "deletePost": {
      "success": true,
      "message": "Post deleted successfully"
    }
  }
}

medium

A. false

B. true

C. null

D. undefined

Solution

1. Step 1: Read the mutation response carefully

   The response shows the success field inside deletePost as true.

2. Step 2: Understand the meaning of success

   A true value means the deletion was successful.

3. Final Answer:

   true -> Option B

4. Quick Check:

   Response success = true [OK]

Hint: Check response JSON for success field value [OK]

Common Mistakes:

• Confusing success with message content
• Assuming success is false without checking response
• Ignoring JSON structure

4.

Identify the error in this delete mutation:

mutation {
  deleteComment(commentId: 456) {
    success
    message
  }
}

medium

A. Missing quotes around the commentId value

B. Missing selection set braces

C. Incorrect mutation keyword

D. Using wrong field names in response

Solution

1. Step 1: Check argument data type

   The commentId is likely a string and should be enclosed in quotes: "456".

2. Step 2: Verify mutation syntax

   The mutation keyword and selection set braces are correct; field names are valid.

3. Final Answer:

   Missing quotes around the commentId value -> Option A

4. Quick Check:

   String IDs need quotes [OK]

Hint: String IDs must be in quotes in mutations [OK]

Common Mistakes:

• Passing string IDs without quotes
• Omitting braces around fields
• Using wrong mutation keyword

5.

You want to delete multiple users by their IDs in one mutation call. Which approach correctly applies the delete mutation pattern?

Options:

1. mutation { deleteUsers(ids: ["1", "2", "3"]) { success message } }
2. mutation { deleteUser(id: "1") { success message } deleteUser(id: "2") { success message } }
3. mutation { deleteUser(id: "1") { success message } }
4. mutation { deleteUsers(ids: "1,2,3") { success message } }

hard

A. Call deleteUser mutation multiple times in one request

B. Pass IDs as a comma-separated string in deleteUsers(ids: "1,2,3")

C. Delete only one user at a time with deleteUser(id: "1")

D. Use a single mutation with an array of IDs: deleteUsers(ids: ["1", "2", "3"])

Solution

1. Step 1: Understand batch deletion

   To delete multiple users at once, the mutation must accept an array of IDs.

2. Step 2: Evaluate options

   Use a single mutation with an array of IDs: deleteUsers(ids: ["1", "2", "3"]) correctly passes an array of strings. Call deleteUser mutation multiple times in one request tries multiple mutations in one call, which is invalid syntax. Delete only one user at a time with deleteUser(id: "1") deletes only one user. Pass IDs as a comma-separated string in deleteUsers(ids: "1,2,3") passes a string instead of an array.

3. Final Answer:

   Use a single mutation with an array of IDs: deleteUsers(ids: ["1", "2", "3"]) -> Option D

4. Quick Check:

   Batch delete uses array of IDs [OK]

Hint: Batch deletes use array arguments, not comma strings [OK]

Common Mistakes:

• Trying multiple mutations in one call
• Passing IDs as comma string instead of array
• Assuming single delete mutation handles multiple IDs