PetstoreAPI GraphQL Protocol Guide

Overview

Protocol: GraphQL over HTTPS Endpoint: https://api.petstoreapi.com/v1/graphql Query Language: GraphQL When to Use GraphQL:

✅ Complex, nested data requirements
✅ Mobile applications (reduce payload size)
✅ Multiple resources in single request
✅ Flexible, self-documenting API
✅ Different clients need different fields

When NOT to Use GraphQL:

❌ Simple CRUD operations (use REST instead)
❌ File uploads (use REST instead)
❌ Need HTTP caching (REST has better caching)

How GraphQL Works

Client                          GraphQL Server
    │                                  │
    ├──── Query ─────────────────────>│
    │  { pets { id name species } }   │
    │                                  │
    │                         ┌────────┴────────┐
    │                         │ Parse Query    │
    │                         │ Validate       │
    │                         │ Execute        │
    │                         └────────┬────────┘
    │                                  │
    │<──── JSON Response ─────────────┤
    │  { "data": { "pets": [...] } }  │

Key Characteristics:

Request exactly the data you need
Single request for multiple resources
Strongly typed schema
Introspection (self-documenting)
No overfetching or underfetching

Basic Queries

List Pets

query GetPets {
  pets {
    id
    name
    species
    breed
    ageMonths
    status
  }
}

Response:

{
  "data": {
    "pets": [
      {
        "id": "019b4132-70aa-764f-b315-e2803d882a24",
        "name": "Buddy",
        "species": "DOG",
        "breed": "Golden Retriever",
        "ageMonths": 24,
        "status": "AVAILABLE"
      }
    ]
  }
}

Get Single Pet

query GetPet($id: ID!) {
  pet(id: $id) {
    id
    name
    species
    breed
    ageMonths
    status
    adoptionFee
    currency
  }
}

Variables:

{
  "id": "019b4132-70aa-764f-b315-e2803d882a24"
}

Filter Pets

query GetAvailableDogs {
  pets(filter: {
    species: DOG
    status: AVAILABLE
    ageRange: { min: 12, max: 36 }
  }) {
    id
    name
    breed
    ageMonths
    adoptionFee
  }
}

Pagination

query GetPetsPaginated {
  pets(page: 1, limit: 20) {
    data {
      id
      name
      species
    }
    pagination {
      page
      limit
      totalItems
      totalPages
    }
  }
}

Mutations

Create Pet

mutation CreatePet {
  createPet(input: {
    name: "Buddy"
    species: DOG
    breed: "Golden Retriever"
    ageMonths: 24
    status: AVAILABLE
    adoptionFee: 150.00
    currency: USD
  }) {
    id
    name
    species
    status
    createdAt
  }
}

Update Pet

mutation UpdatePet($id: ID!) {
  updatePet(
    id: $id
    input: {
      status: PENDING
      ageMonths: 25
    }
  ) {
    id
    name
    status
    ageMonths
    updatedAt
  }
}

Delete Pet

mutation DeletePet($id: ID!) {
  deletePet(id: $id) {
    id
    name
    success
    message
  }
}

Nested Queries

Pet with Owner

query GetPetWithOwner {
  pet(id: "pet_fYrZzCW9E1WIOyGw") {
    id
    name
    species
    owner {
      id
      username
      email
      avatar {
        url
      }
    }
  }
}

Order with Items

query GetOrderWithItems {
  order(id: "019b4141-e5f3-a1b7-c4d8-9f6e2a5b8c1d") {
    id
    status
    total
    currency
    items {
      productId
      quantity
      price
      product {
        name
        description
      }
    }
    shippingAddress {
      street
      city
      state
      country
      postalCode
    }
  }
}

Authentication

Include JWT token in Authorization header:

curl -X POST https://api.petstoreapi.com/v1/graphql \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_JWT_TOKEN" \
  -d '{
    "query": "query GetPets { pets { id name species } }"
  }'

Code Examples

JavaScript (fetch)

async function graphqlQuery(query, variables = {}) {
  const response = await fetch('https://api.petstoreapi.com/v1/graphql', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Authorization': `Bearer ${token}`
    },
    body: JSON.stringify({ query, variables })
  });

  const { data, errors } = await response.json();

  if (errors) {
    throw new Error(errors[0].message);
  }

  return data;
}

// Get pets
const data = await graphqlQuery(`
  query GetAvailablePets {
    pets(filter: { status: AVAILABLE }) {
      id
      name
      species
      adoptionFee
    }
  }
`);

console.log(data.pets);

JavaScript (Apollo Client)

import { ApolloClient, InMemoryCache, gql } from '@apollo/client';

const client = new ApolloClient({
  uri: 'https://api.petstoreapi.com/v1/graphql',
  cache: new InMemoryCache(),
  headers: {
    'Authorization': `Bearer ${token}`
  }
});

// Query
const GET_PETS = gql`
  query GetPets($species: PetSpecies) {
    pets(filter: { species: $species }) {
      id
      name
      species
      breed
    }
  }
`;

const { data } = await client.query({
  query: GET_PETS,
  variables: { species: 'DOG' }
});

// Mutation
const CREATE_PET = gql`
  mutation CreatePet($input: CreatePetInput!) {
    createPet(input: $input) {
      id
      name
      species
    }
  }
`;

const { data: newPet } = await client.mutate({
  mutation: CREATE_PET,
  variables: {
    input: {
      name: 'Buddy',
      species: 'DOG',
      ageMonths: 24
    }
  }
});

Python (gql)

from gql import gql, Client
from gql.transport.requests import RequestsHTTPTransport

transport = RequestsHTTPTransport(
    url='https://api.petstoreapi.com/v1/graphql',
    headers={'Authorization': f'Bearer {token}'}
)

client = Client(transport=transport, fetch_schema_from_transport=True)

# Query
query = gql('''
  query GetPets {
    pets {
      id
      name
      species
    }
  }
''')

result = client.execute(query)
print(result['pets'])

# Mutation
mutation = gql('''
  mutation CreatePet($input: CreatePetInput!) {
    createPet(input: $input) {
      id
      name
      species
    }
  }
''')

result = client.execute(mutation, variable_values={
    'input': {
        'name': 'Buddy',
        'species': 'DOG',
        'ageMonths': 24
    }
})

Advanced Features

Fragments

Reuse common fields:

fragment PetFields on Pet {
  id
  name
  species
  breed
  ageMonths
}

query GetPets {
  pets {
    ...PetFields
  }
}

query GetPet($id: ID!) {
  pet(id: $id) {
    ...PetFields
    adoptionFee
  }
}

Directives

Conditionally include fields:

query GetPet($id: ID!, $withFee: Boolean!) {
  pet(id: $id) {
    id
    name
    species
    adoptionFee @include(if: $withFee)
  }
}

Aliases

Rename fields in response:

query GetPets {
  dogs: pets(filter: { species: DOG }) {
    id
    name
  }
  cats: pets(filter: { species: CAT }) {
    id
    name
  }
}

Multiple Queries

query GetDashboardData {
  availablePets: pets(filter: { status: AVAILABLE }) {
    id
    name
  }
  pendingOrders: orders(filter: { status: PENDING }) {
    id
    total
  }
  recentAdoptions: adoptions(limit: 5) {
    id
    date
  }
}

Introspection

Query the schema:

query {
  __schema {
    types {
      name
      description
    }
  }
}

Get type details:

query {
  __type(name: "Pet") {
    name
    description
    fields {
      name
      type {
        name
      }
    }
  }
}

Best Practices

1. Use Specific Fields

# Good - specific fields
query {
  pets {
    id
    name
  }
}

# Bad - too many fields
query {
  pets {
    id
    name
    species
    breed
    ageMonths
    status
    adoptionFee
    currency
    description
    # ... many more fields
  }
}

2. Batch Queries

# Good - single request
query GetDashboard {
  stats { totalPets totalOrders }
  recentPets { id name }
  recentOrders { id total }
}

# Bad - multiple requests
# query 1: stats
# query 2: recentPets
# query 3: recentOrders

3. Use Fragments for Reuse

fragment PetSummary on Pet {
  id
  name
  species
  status
}

# Use in multiple queries
query { pets { ...PetSummary } }
query { pet(id: "123") { ...PetSummary } }

Error Handling

GraphQL errors are returned in the response:

{
  "data": {
    "pet": null
  },
  "errors": [
    {
      "message": "Pet not found",
      "path": ["pet"],
      "extensions": {
        "code": "PET_NOT_FOUND"
      }
    }
  ]
}

Handle errors in code:

const { data, errors } = await client.query({ query });

if (errors) {
  errors.forEach(error => {
    console.error(error.message);
  });
}

if (data?.pet) {
  // Process pet
}

Comparison with REST

Feature	GraphQL	REST
Data Fetching	Exact fields	Fixed responses
Requests	Single for multiple resources	Multiple endpoints
Overfetching	No	Yes (often)
Underfetching	No	Yes (n+1 problem)
Caching	Complex	HTTP caching built-in
Schema	Strongly typed	Varies
Documentation	Self-documenting	Separate (OpenAPI)

Interactive Documentation

GraphQL Playground: https://api.petstoreapi.com/v1/graphql
Protocol Overview: All Protocols
REST API Guide: REST Protocol

Getting Started

Protocol Guides

Overview

How GraphQL Works

Basic Queries

List Pets

Get Single Pet

Filter Pets

Mutations

Create Pet

Update Pet

Delete Pet

Nested Queries

Pet with Owner

Order with Items

Authentication

Code Examples

JavaScript (fetch)

JavaScript (Apollo Client)

Python (gql)

Advanced Features

Fragments

Directives

Aliases

Multiple Queries

Introspection

Best Practices

1. Use Specific Fields

2. Batch Queries

3. Use Fragments for Reuse

Error Handling

Comparison with REST

Interactive Documentation

Getting Started

Protocol Guides

​Overview

​How GraphQL Works

​Basic Queries

​List Pets

​Get Single Pet

​Filter Pets

​Pagination

​Mutations

​Create Pet

​Update Pet

​Delete Pet

​Nested Queries

​Pet with Owner

​Order with Items

​Authentication

​Code Examples

​JavaScript (fetch)

​JavaScript (Apollo Client)

​Python (gql)

​Advanced Features

​Fragments

​Directives

​Aliases

​Multiple Queries

​Introspection

​Best Practices

​1. Use Specific Fields

​2. Batch Queries

​3. Use Fragments for Reuse

​Error Handling

​Comparison with REST

​Interactive Documentation

​Related Resources

Overview

How GraphQL Works

Basic Queries

List Pets

Get Single Pet

Filter Pets

Pagination

Mutations

Create Pet

Update Pet

Delete Pet

Nested Queries

Pet with Owner

Order with Items

Authentication

Code Examples

JavaScript (fetch)

JavaScript (Apollo Client)

Python (gql)

Advanced Features

Fragments

Directives

Aliases

Multiple Queries

Introspection

Best Practices

1. Use Specific Fields

2. Batch Queries

3. Use Fragments for Reuse

Error Handling

Comparison with REST

Interactive Documentation

Related Resources