Lesson 33 of 40 Web Development Advanced 50 min

GraphQL APIs with Hot Chocolate

Build flexible, schema-first GraphQL APIs using Hot Chocolate 15 with VS 2026's integrated schema explorer and query analyzer.

Part 1: Schema-First with Hot Chocolate

public class Query
{
  [UseProjection][UseFiltering][UseSorting]
  public IQueryable<Order> GetOrders([Service] AppDbContext ctx)
    => ctx.Orders.AsQueryable();
}

Part 2: Mutations

public class Mutation
{
  public async Task<Order> CreateOrder(
    CreateOrderInput input,
    [Service] IOrderService service)
  {
    return await service.CreateAsync(input);
  }
}

Part 3: Subscriptions

public class Subscription
{
  [Subscribe][Topic("OrderCreated")]
  public Order OnOrderCreated([EventMessage] Order order)
    => order;
}

// Trigger from mutation:
await sender.SendAsync("OrderCreated", newOrder);

Part 4: DataLoader for N+1 Prevention

public class CustomerByIdDataLoader : BatchDataLoader<int, Customer>
{
  protected override async Task<IReadOnlyDictionary<int,Customer>> LoadBatchAsync(
    IReadOnlyList<int> keys, CancellationToken ct)
  => await _db.Customers.Where(c => keys.Contains(c.Id))
    .ToDictionaryAsync(c => c.Id);