GraphQL Schema Patterns

When to Use

Use this skill when you need graphQL queries, mutations, and code generation patterns. Use when creating GraphQL operations, working with Apollo Client, or generating types.

Core Rules

1. NEVER inline gql literals - Create .gql files
2. ALWAYS run codegen after creating/modifying .gql files
3. ALWAYS add onError handler to mutations
4. Use generated hooks - Never write raw Apollo hooks

File Structure

src/
├── components/
│   └── ItemList/
│       ├── ItemList.tsx
│       ├── GetItems.gql           # Query definition
│       └── GetItems.generated.ts  # Auto-generated (don't edit)
└── graphql/
    └── mutations/
        └── CreateItem.gql         # Shared mutations

Creating a Query

Step 1: Create .gql file

# src/components/ItemList/GetItems.gql
query GetItems($limit: Int, $offset: Int) {
  items(limit: $limit, offset: $offset) {
    id
    name
    description
    createdAt
  }
}

Step 2: Run codegen

npm run gql:typegen

Step 3: Import and use generated hook

import { useGetItemsQuery } from './GetItems.generated';

const ItemList = () => {
  const { data, loading, error, refetch } = useGetItemsQuery({
    variables: { limit: 20, offset: 0 },
  });

  if (error) return <ErrorState error={error} onRetry={refetch} />;
  if (loading && !data) return <LoadingSkeleton />;
  if (!data?.items.length) return <EmptyState />;

  return <List items={data.items} />;
};

Creating a Mutation

Step 1: Create .gql file

# src/graphql/mutations/CreateItem.gql
mutation CreateItem($input: CreateItemInput!) {
  createItem(input: $input) {
    id
    name
    description
  }
}

Step 2: Run codegen

npm run gql:typegen

Step 3: Use with REQUIRED error handling

import { useCreateItemMutation } from 'graphql/mutations/CreateItem.generated';

const CreateItemForm = () => {
  const [createItem, { loading }] = useCreateItemMutation({
    // Success handling
    onCompleted: (data) => {
      toast.success({ title: 'Item created' });
      navigation.goBack();
    },
    // ERROR HANDLING IS REQUIRED
    onError: (error) => {
      console.error('createItem failed:', error);
      toast.error({ title: 'Failed to create item' });
    },
    // Cache update
    update: (cache, { data }) => {
      if (data?.createItem) {
        cache.modify({
          fields: {
            items: (existing = []) => [...existing, data.createItem],
          },
        });
      }
    },
  });

  return (
    <Button
      onPress={() => createItem({ variables: { input: formValues } })}
      isDisabled={!isValid || loading}
      isLoading={loading}
    >
      Create
    </Button>
  );
};

Mutation UI Requirements

CRITICAL: Every mutation trigger must:

1. Be disabled during mutation - Prevent double-clicks
2. Show loading state - Visual feedback
3. Have onError handler - User knows it failed
4. Show success feedback - User knows it worked

// CORRECT - Complete mutation pattern
const [submit, { loading }] = useSubmitMutation({
  onError: (error) => {
    console.error('submit failed:', error);
    toast.error({ title: 'Save failed' });
  },
  onCompleted: () => {
    toast.success({ title: 'Saved' });
  },
});

<Button
  onPress={handleSubmit}
  isDisabled={!isValid || loading}
  isLoading={loading}
>
  Submit
</Button>

Query Options

Fetch Policies

Common Options

useGetItemsQuery({
  variables: { id: itemId },

  // Fetch strategy
  fetchPolicy: 'cache-and-network',

  // Re-render on network status changes
  notifyOnNetworkStatusChange: true,

  // Skip if condition not met
  skip: !itemId,

  // Poll for updates
  pollInterval: 30000,
});

Optimistic Updates

For instant UI feedback:

const [toggleFavorite] = useToggleFavoriteMutation({
  optimisticResponse: {
    toggleFavorite: {
      __typename: 'Item',
      id: itemId,
      isFavorite: !currentState,
    },
  },
  onError: (error) => {
    // Rollback happens automatically
    console.error('toggleFavorite failed:', error);
    toast.error({ title: 'Failed to update' });
  },
});

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