useMutation hook in GraphQL - Step-by-Step Execution

Concept Flow - useMutation hook

Component Renders

↓

Call useMutation

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Get mutate function + state

↓

User triggers mutation

↓

mutate function sends request

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Server processes mutation

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Response received

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Update mutation state

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Component re-renders with new state

The useMutation hook provides a function to send mutation requests and tracks their state, updating the component when the mutation completes.

Execution Sample

GraphQL

const [addTodo, { data, loading, error }] = useMutation(ADD_TODO);

// On button click
addTodo({ variables: { text: 'Buy milk' } });

This code sets up a mutation function to add a todo item and calls it with variables when triggered.

Execution Table

Step	Action	Mutation Function State	Loading	Data	Error
1	Component renders and calls useMutation	Ready	false	null	null
2	User clicks button to add todo	Called	true	null	null
3	Mutation request sent to server	In Progress	true	null	null
4	Server processes mutation	In Progress	true	null	null
5	Server responds with new todo data	Completed	false	{"id": 1, "text": "Buy milk"}	null
6	Component re-renders with updated data	Ready	false	{"id": 1, "text": "Buy milk"}	null

💡 Mutation completes when server response is received and state updates to Completed.

Variable Tracker

Variable	Start	After Step 2	After Step 5	Final
loading	false	true	false	false
data	null	null	{"id": 1, "text": "Buy milk"}	{"id": 1, "text": "Buy milk"}
error	null	null	null	null

Key Moments - 3 Insights

Why is loading true immediately after calling the mutation function?

Loading becomes true right after the mutation function is called (see Step 2) because the request is now in progress and the hook tracks this state.

When does the data variable get updated with the server response?

Data updates only after the server responds successfully (see Step 5), not before.

What happens if the mutation fails? How does error change?

If the mutation fails, error would be set with the error info and loading would become false, but in this trace error remains null because mutation succeeds.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of loading at Step 3?

A false

B true

C null

D undefined

💡 Hint

Check the 'Loading' column at Step 3 in the execution_table.

At which step does the mutation state change to Completed?

A Step 5

B Step 4

C Step 2

D Step 6

💡 Hint

Look for 'Completed' in the 'Mutation Function State' column.

If the server response was an error, which variable would change in variable_tracker?

A loading

B data

C error

D none

💡 Hint

Errors are tracked in the 'error' variable in variable_tracker.

Concept Snapshot

useMutation hook syntax:
const [mutateFunction, { data, loading, error }] = useMutation(MUTATION);

- Call mutateFunction({ variables }) to run mutation
- loading is true while request is in progress
- data holds server response on success
- error holds error info on failure
- Component re-renders on state changes

Full Transcript

The useMutation hook in GraphQL provides a function to send mutation requests and tracks the request state. When the component renders, useMutation returns a mutate function and an object with loading, data, and error states. When the mutate function is called, loading becomes true as the request is sent. Once the server responds, loading becomes false and data updates with the response. If an error occurs, error updates accordingly. The component re-renders whenever these states change, allowing UI updates based on mutation progress and results.