Update mutation pattern in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this update mutation?

Given the following GraphQL mutation to update a user's email, what will be the returned data?

GraphQL

mutation {
  updateUser(id: "123", input: {email: "[e-mail]"}) {
    id
    name
    email
  }
}

A { "data": { "updateUser": null } }

B { "data": { "updateUser": { "id": "123", "name": "Alice", "email": "[e-mail]" } } }

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

D { "data": { "updateUser": { "id": "123", "name": "Alice", "email": "[e-mail]" } } }

💡 Hint

Consider what the mutation is intended to do and what fields it returns.

The mutation updates the user's email and returns the updated user data including the new email.

📝 Syntax

intermediate

Identify the syntax error in this update mutation

Which option correctly fixes the syntax error in this GraphQL update mutation?

GraphQL

mutation {
  updateUser(id: "123", input: {email: "[e-mail]" ) {
    id
    email
  }
}

A

mutation {
  updateUser(id: "123", input: {email: [e-mail]}) {
    id
    email
  }
}

B

mutation {
  updateUser(id: "123", input: email: "[e-mail]") {
    id
    email
  }
}

C

mutation {
  updateUser(id: "123", input: {email: "[e-mail]"}) {
    id
    email
  }
}

D

mutation {
  updateUser(id: "123", input: {email: "[e-mail]"} {
    id
    email
  }
}

💡 Hint

Check for matching brackets and correct input object syntax.

Option C correctly closes the input object with a closing brace and parenthesis.

❓ optimization

advanced

Optimize this update mutation for minimal data transfer

You want to update only the user's phone number and receive only the updated phone number in response. Which mutation is best?

GraphQL

mutation {
  updateUser(id: "123", input: {phone: "[phone]"}) {
    id
    name
    email
    phone
  }
}

A

mutation {
  updateUser(id: "123", input: {phone: "[phone]"}) {
    id
    name
    email
    phone
  }
}

B

mutation {
  updateUser(id: "123", input: {phone: "[phone]"}) {
    id
    phone
  }
}

C

mutation {
  updateUser(id: "123", input: {phone: "[phone]"}) {
    id
    name
    phone
  }
}

D

mutation {
  updateUser(id: "123", input: {phone: "[phone]"}) {
    phone
  }
}

💡 Hint

Request only the fields you need to reduce data size.

Option D requests only the updated phone field, minimizing data transfer.

🔧 Debug

advanced

Why does this update mutation fail with an error?

Given this mutation, why does it return an error?

GraphQL

mutation {
  updateUser(input: {email: "[e-mail]"}) {
    id
    email
  }
}

A The mutation is missing the required 'id' argument to identify which user to update.

B The input object is incorrectly formatted; it should be a list.

C The mutation is missing a selection set inside the input object.

D The mutation should use 'updateUsers' instead of 'updateUser'.

💡 Hint

Check the required arguments for update mutations.

Update mutations typically require an identifier to specify which record to update.

🧠 Conceptual

expert

What is the main advantage of using input types in update mutations?

Why do GraphQL update mutations commonly use input types for the data to update?

A Input types allow grouping multiple fields into a single argument, improving clarity and validation.

B Input types automatically update all fields in the database without specifying them.

C Input types make the mutation run faster by caching the data.

D Input types are required to use subscriptions with mutations.

💡 Hint

Think about how input types help organize mutation arguments.

Input types group related fields and enable schema validation, making mutations clearer and safer.

Practice

1. What is the main purpose of an update mutation in GraphQL?

easy

A. To create new data records

B. To change existing data by specifying an ID and new values

C. To delete data from the database

D. To fetch data without any changes

Solution

1. Step 1: Understand the role of update mutations

   Update mutations modify existing records by identifying them and applying new values.

2. Step 2: Differentiate from other mutation types

   Delete mutations remove data, create mutations add new data, and queries fetch data without changes.

3. Final Answer:

   To change existing data by specifying an ID and new values -> Option B

4. Quick Check:

   Update mutation = change existing data [OK]

Hint: Update mutations modify existing records by ID [OK]

Common Mistakes:

• Confusing update with create or delete mutations
• Thinking update fetches data without changes
• Assuming update creates new records

2. Which of the following is the correct syntax for an update mutation in GraphQL?

easy

A. mutation { updateUser(id: "123", input: {name: "Alice"}) { id name } }

B. mutation { createUser(id: "123", input: {name: "Alice"}) { id name } }

C. query { updateUser(id: "123", input: {name: "Alice"}) { id name } }

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

Solution

1. Step 1: Identify the mutation keyword and operation

   Update mutations use the mutation keyword and specify the update operation with an ID and input object.

2. Step 2: Check the options for correct mutation syntax

   mutation { updateUser(id: "123", input: {name: "Alice"}) { id name } } uses mutation with updateUser and input fields correctly; others use wrong operation or query keyword.

3. Final Answer:

   mutation { updateUser(id: "123", input: {name: "Alice"}) { id name } } -> Option A

4. Quick Check:

   Update mutation syntax = mutation + update operation + input [OK]

Hint: Update mutations use 'mutation' keyword with update operation [OK]

Common Mistakes:

• Using 'query' instead of 'mutation'
• Using create or delete operation instead of update
• Missing input object for new values

3. Given this mutation:

mutation { updatePost(id: "5", input: {title: "New Title"}) { id title content } }

What will be the output if the post with ID 5 exists and has content "Old content"?

medium

A. { "data": { "updatePost": null } }

B. { "data": { "updatePost": { "id": "5", "title": "Old Title", "content": "Old content" } } }

C. { "data": { "updatePost": { "id": "5", "title": "New Title", "content": "Old content" } } }

D. Error: Post with ID 5 not found

Solution

1. Step 1: Understand the mutation effect

   The mutation updates the post with ID 5, changing only the title to "New Title" while keeping other fields unchanged.

2. Step 2: Predict the returned data

   The response includes the updated title and the unchanged content "Old content" along with the ID.

3. Final Answer:

   { "data": { "updatePost": { "id": "5", "title": "New Title", "content": "Old content" } } } -> Option C

4. Quick Check:

   Update mutation returns updated fields plus unchanged fields [OK]

Hint: Update changes specified fields, others remain same [OK]

Common Mistakes:

• Assuming all fields reset or become null
• Expecting error when post exists
• Ignoring unchanged fields in output

4. Identify the error in this update mutation:

mutation { updateUser(input: {name: "Bob"}) { id name } }

medium

A. Missing the ID argument to specify which user to update

B. Input object should be named 'data' instead of 'input'

C. Mutation keyword should be 'query' instead of 'mutation'

D. Cannot update the 'name' field

Solution

1. Step 1: Check required arguments for update mutation

   Update mutations require an ID to identify the record to update.

2. Step 2: Analyze the given mutation

   The mutation lacks the ID argument, so it cannot know which user to update.

3. Final Answer:

   Missing the ID argument to specify which user to update -> Option A

4. Quick Check:

   Update mutation must include ID argument [OK]

Hint: Always include ID to update specific record [OK]

Common Mistakes:

• Omitting the ID argument
• Confusing input object name
• Using 'query' instead of 'mutation'

5. You want to update a user's email and phone number but only if the phone number is provided. Which mutation pattern correctly handles this conditional update?

mutation UpdateUser($id: ID!, $email: String!, $phone: String) {
  updateUser(id: $id, input: {email: $email, phone: $phone}) {
    id
    email
    phone
  }
}

hard

A. Create separate mutations for email and phone updates

B. Always send phone field with empty string if no update needed

C. Use optional input fields and send null for phone if not updating

D. Remove phone field from input object when not updating

Solution

1. Step 1: Understand conditional updates in GraphQL

   To update only provided fields, omit fields not meant to be changed from the input object.

2. Step 2: Analyze options for handling optional phone

   Sending null or empty string may overwrite data; omitting the phone field avoids unintended changes.

3. Final Answer:

   Remove phone field from input object when not updating -> Option D

4. Quick Check:

   Omit fields to keep existing values unchanged [OK]

Hint: Omit fields to avoid overwriting unchanged data [OK]

Common Mistakes:

• Sending null overwrites existing data
• Using empty string instead of omitting field
• Creating unnecessary multiple mutations