Update mutation pattern in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an update mutation in GraphQL?

An update mutation is a GraphQL operation that changes existing data on the server, such as modifying a record's fields.

beginner

In an update mutation, why do we usually provide an id or unique identifier?

The id tells the server which specific record to update, ensuring the correct data is changed.

beginner

What does the input argument typically contain in an update mutation?

It contains the new values for the fields you want to change in the record.

beginner

Why is it important to specify the fields you want back in the response after an update mutation?

To confirm the update worked and to get the latest data from the server.

beginner

Show a simple example of an update mutation to change a user's email.

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

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

A To change existing data on the server

B To delete data from the server

C To create new data on the server

D To retrieve data from the server

Update mutations are used to change existing data, not to retrieve, delete, or create new data.

Which argument usually identifies the record to update in a mutation?

A id

B input

C fields

D type

The 'id' argument uniquely identifies which record to update.

What should you include in the mutation response to verify the update?

A Only the id

B The updated fields

C The server status code

D Nothing, response is empty

Including updated fields in the response confirms the changes.

In the mutation syntax, where do you put the new values for the update?

A In the query name

B In the response fields

C In the input argument

D In the variables section only

New values are passed inside the input argument.

Which of these is a valid update mutation example?

A mutation { deleteUser(id: "1") { id } }

B query { updateUser(id: "1") { name } }

C mutation { createUser(input: { name: "Alice" }) { id } }

D mutation { updateUser(id: "1", input: { name: "Alice" }) { id name } }

Option D correctly shows an update mutation with id and input.

Explain the steps to write an update mutation in GraphQL.

Think about what you need to tell the server to change and what you want back.

Describe why it is helpful to request updated fields in the mutation response.

Imagine you want to see the changes immediately after updating.

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