Writing GRAPHQL Operations

GraphQL Operations Developer

Purpose

Guide the creation and maintenance of GraphQL operations following project conventions for type safety, organization, error handling, and testing.

When to Use

• Creating new GraphQL queries or mutations
• Integrating with Saleor API endpoints
• Updating schema after Saleor changes
• Working with urql client configuration
• Creating mocks for testing

Table of Contents

• Project GraphQL Stack
• File Organization
• Creating Operations with gql.tada
• Repository Pattern
• Error Handling
• Schema Management
• Testing GraphQL Operations
• Client Configuration
• Best Practices
• References

Project GraphQL Stack

File Organization

src/lib/graphql/
├── client.ts              # urql client configuration
├── operations/            # GraphQL operation definitions
│   ├── products.ts
│   ├── categories.ts
│   └── ...
├── fragments/             # Reusable GraphQL fragments
│   └── ...
├── __mocks__/            # Test mocks
│   └── ...
└── schema.graphql        # Saleor schema (generated)

src/modules/<entity>/
├── repository.ts          # Uses GraphQL operations
└── ...

Creating Operations with gql.tada

Basic Query

import { graphql } from 'gql.tada';

// gql.tada infers types from schema automatically
export const GetCategoriesQuery = graphql(`
  query GetCategories($first: Int!) {
    categories(first: $first) {
      edges {
        node {
          id
          name
          slug
          description
          parent {
            id
            slug
          }
        }
      }
    }
  }
`);

// Type is inferred automatically
type GetCategoriesResult = ResultOf<typeof GetCategoriesQuery>;

Query with Variables

export const GetCategoryBySlugQuery = graphql(`
  query GetCategoryBySlug($slug: String!) {
    category(slug: $slug) {
      id
      name
      slug
      description
      level
      parent {
        id
        slug
      }
      children(first: 100) {
        edges {
          node {
            id
            name
            slug
          }
        }
      }
    }
  }
`);

Mutation

export const CreateCategoryMutation = graphql(`
  mutation CreateCategory($input: CategoryInput!) {
    categoryCreate(input: $input) {
      category {
        id
        name
        slug
      }
      errors {
        field
        message
        code
      }
    }
  }
`);

Using Fragments

// Define reusable fragment
export const CategoryFieldsFragment = graphql(`
  fragment CategoryFields on Category {
    id
    name
    slug
    description
    level
  }
`);

// Use in query
export const GetCategoriesWithFragmentQuery = graphql(`
  query GetCategoriesWithFragment($first: Int!) {
    categories(first: $first) {
      edges {
        node {
          ...CategoryFields
        }
      }
    }
  }
`, [CategoryFieldsFragment]);

Repository Pattern

Standard Repository Structure

// src/modules/category/repository.ts
import { Client } from '@urql/core';
import { graphql } from 'gql.tada';
import { GraphQLError } from '@/lib/errors';

const GetCategoriesQuery = graphql(`...`);
const CreateCategoryMutation = graphql(`...`);

export class CategoryRepository {
  constructor(private readonly client: Client) {}

  async findAll(): Promise<Category[]> {
    const result = await this.client.query(GetCategoriesQuery, { first: 100 });

    if (result.error) {
      throw GraphQLError.fromCombinedError(result.error, 'GetCategories');
    }

    return this.mapCategories(result.data?.categories);
  }

  async create(input: CategoryInput): Promise<Category> {
    const result = await this.client.mutation(CreateCategoryMutation, { input });

    if (result.error) {
      throw GraphQLError.fromCombinedError(result.error, 'CreateCategory');
    }

    if (result.data?.categoryCreate?.errors?.length) {
      throw new GraphQLError(
        'Category creation failed',
        result.data.categoryCreate.errors
      );
    }

    return this.mapCategory(result.data?.categoryCreate?.category);
  }

  // Map GraphQL response to domain model
  private mapCategory(gqlCategory: GqlCategory | null): Category {
    if (!gqlCategory) {
      throw new EntityNotFoundError('Category not found');
    }
    return {
      id: gqlCategory.id,
      name: gqlCategory.name,
      slug: gqlCategory.slug,
      description: gqlCategory.description ?? undefined,
    };
  }
}

Error Handling

Wrapping GraphQL Errors

import { CombinedError } from '@urql/core';
import { GraphQLError } from '@/lib/errors';

// In repository methods
if (result.error) {
  throw GraphQLError.fromCombinedError(
    result.error,
    'OperationName',
    { entitySlug: input.slug }  // Additional context
  );
}

// Handle mutation-specific errors
if (result.data?.mutationName?.errors?.length) {
  const errors = result.data.mutationName.errors;
  throw new GraphQLError(
    `Operation failed: ${errors.map(e => e.message).join(', ')}`,
    errors
  );
}

Common Error Scenarios

Schema Management

Updating Schema

# Fetch latest schema from Saleor instance
pnpm fetch-schema

# This updates:
# - src/lib/graphql/schema.graphql
# - graphql-env.d.ts (type definitions)

When to Update Schema

• New Saleor features needed
• After Saleor version upgrade
• When encountering schema drift errors
• Commit schema changes with feature implementation

Testing GraphQL Operations

Mock Setup with MSW

// src/lib/graphql/__mocks__/category-mocks.ts
import { graphql, HttpResponse } from 'msw';

export const categoryHandlers = [
  graphql.query('GetCategories', () => {
    return HttpResponse.json({
      data: {
        categories: {
          edges: [
            {
              node: {
                id: 'cat-1',
                name: 'Electronics',
                slug: 'electronics',
              },
            },
          ],
        },
      },
    });
  }),

  graphql.mutation('CreateCategory', ({ variables }) => {
    return HttpResponse.json({
      data: {
        categoryCreate: {
          category: {
            id: 'new-cat',
            name: variables.input.name,
            slug: variables.input.slug,
          },
          errors: [],
        },
      },
    });
  }),
];

Repository Test Pattern

describe('CategoryRepository', () => {
  const server = setupServer(...categoryHandlers);

  beforeAll(() => server.listen());
  afterEach(() => server.resetHandlers());
  afterAll(() => server.close());

  it('should fetch all categories', async () => {
    const repository = new CategoryRepository(testClient);
    const categories = await repository.findAll();

    expect(categories).toHaveLength(1);
    expect(categories[0].slug).toBe('electronics');
  });
});

Client Configuration

urql Client Setup

// src/lib/graphql/client.ts
import { Client, cacheExchange, fetchExchange } from '@urql/core';
import { authExchange } from '@urql/exchange-auth';
import { retryExchange } from '@urql/exchange-retry';

export const createClient = (url: string, token: string) => {
  return new Client({
    url,
    exchanges: [
      cacheExchange,
      authExchange(async utils => ({
        addAuthToOperation(operation) {
          return utils.appendHeaders(operation, {
            Authorization: `Bearer ${token}`,
          });
        },
      })),
      retryExchange({
        initialDelayMs: 1000,
        maxDelayMs: 15000,
        maxNumberAttempts: 5,
        retryIf: error => {
          // Retry on rate limits and network errors
          return error?.response?.status === 429 || !error?.response;
        },
      }),
      fetchExchange,
    ],
  });
};

Best Practices

Do's

• Use gql.tada for all operations (type inference)
• Keep operations close to their domain modules
• Map GraphQL responses to domain models
• Include operation name in error context
• Update mocks when schema changes

Don'ts

• Don't use raw string queries (no type safety)
• Don't expose GraphQL types directly to services
• Don't skip error handling for any operation
• Don't hardcode pagination limits (use constants)

Validation Checkpoints

Common Mistakes

External Documentation

For up-to-date library docs, use Context7 MCP:

• urql: mcp__context7__get-library-docs with /urql-graphql/urql
• gql.tada: Use mcp__context7__resolve-library-id with "gql.tada"

References

Skill Reference Files

• Error Handling - Error types, wrapping, and recovery patterns
• Fragment Patterns - Fragment composition and type inference

Project Resources

• {baseDir}/src/lib/graphql/client.ts - Client configuration
• {baseDir}/src/lib/graphql/operations/ - Existing operations
• {baseDir}/docs/CODE_QUALITY.md#graphql--external-integrations - Quality standards

Related Skills

• Complete entity workflow: See adding-entity-types for full implementation including bulk mutations
• Bulk operations: See adding-entity-types/references/bulk-mutations.md for chunking patterns
• Testing GraphQL: See analyzing-test-coverage for MSW setup