Top 15 GraphQL Interview Questions and Answers

// Define a subscription type
public class Subscription
{
    [Subscribe]
    [Topic("OnTextChanged")]
    public DocumentChangedPayload OnTextChanged([EventMessage] DocumentChangedEvent message) =>
        new DocumentChangedPayload(message);
}

// Event payload
public class DocumentChangedPayload
{
    public DocumentChangedPayload(DocumentChangedEvent message)
    {
        TextContent = message.TextContent;
    }

    public string TextContent { get; }
}

// Publish updates from a mutation resolver
public class Mutation
{
    public async Task UpdateText(UpdateTextInput input, [Service] IEventSender eventSender)
    {
        var textContent = UpdateTextDocument(input.TextContent);

        await eventSender.SendAsync(new DocumentChangedEvent(textContent));

        return new DocumentChangedPayload(new DocumentChangedEvent(textContent));
    }
}
    

// Authorization directive
public class AuthDirectiveType : AuthorizationDirectiveType
{
    protected override async Task AuthorizeResolveAsync(AuthDirective directive, OperationContext context)
    {
        // Get user roles from the context
        var roles = context.GetUserRoles();

        // Check if the user has the required role
        return roles.Contains(directive.Role);
    }
}

// Usage in the schema
type Mutation {
    createPost(input: CreatePostInput!): Post! @auth(role: "AUTHOR")
    updatePost(input: UpdatePostInput!): Post @auth(role: "AUTHOR")
}
    

• Managing and scaling the WebSocket connections
• Ensuring reliable message delivery and handling disconnections
• Implementing authentication and authorization for subscriptions
• Preventing excessive resource consumption from subscriptions

• Using a dedicated WebSocket server or service (e.g., Apollo Server with Redis) for better scalability
• Implementing connection pooling and rate-limiting mechanisms
• Integrating with existing authentication/authorization systems
• Implementing subscription filters and validations to limit data exposure
• Monitoring and alerting for subscription-related issues

const mockUser = {
  id: '123',
  name: 'John Doe',
  email: 'john@example.com',
};

const mockResolvers = {
  Query: {
    getUser: () => mockUser,
  },
};

• Resolving data from multiple services for a single query
• Managing service discovery and communication between services
• Handling errors and partial data responses from services
• Ensuring performance and avoiding over-fetching or under-fetching data

• Using Schema Stitching or Federation to combine schemas from multiple services
• Implementing a service mesh or API gateway to handle service discovery and communication
• Using techniques like batched resolvers or data loaders to optimize data fetching
• Implementing robust error handling and fallback mechanisms
• Identifying performance issues in database queries through monitoring and profiling

• Additional storage and management overhead for the query store
• Potential security risks if query signatures are not properly validated or sanitized
• Challenges with cache invalidation and stale data handling
• Potential issues with schema changes or updates, which may require invalidating the query store

• Ensuring that data and resources are properly isolated between tenants
• Implementing tenant-aware access control and authorization mechanisms
• Preventing data leakage or unauthorized access across tenants
• Optimizing query performance and avoiding cross-tenant data fetching

• Implementing a tenant-aware resolver layer that filters and scopes data based on the current tenant context
• Using techniques like query whitelisting or schema directives to enforce tenant-specific access control rules
• Implementing tenant-aware caching and batching mechanisms to optimize performance
• Using database-level data partitioning or separate data stores for each tenant, if feasible
• Implementing robust monitoring and auditing mechanisms to detect potential security or performance issues

// Enable persisted queries
services.AddGraphQLServer()
    .AddPersistedQueryPipeline()
    .AddQueryType()
    .AddMutationType();

// Cache control middleware
app.UseGraphQLServer(options =>
{
    options.UsePersistedQueryPipeline();
    options.UseCacheControl(cacheControl =>
    {
        cacheControl.MaxAge = 45; // Cache for 45 seconds
        cacheControl.Public();
    });
});
    

// Define a mutation for file upload
public class Mutation
{
    [UseUploadSingle] // Handles single file uploads
    public async Task UploadFileSingle(IFile file, [Service] IFileStorage fileStorage)
    {
        var fileId = await fileStorage.SaveFileAsync(file.OpenReadStream(), file.FileName);
        return new UploadResult(fileId);
    }
}

// File storage service
public class FileStorage : IFileStorage
{
    public async Task SaveFileToStorageAsync(Stream stream, string fileName)
    {
        // Save the file to storage and return a unique file ID
        // ...
    }
}
    

        
            // Define schemas
ISchema productSchema = SchemaBuilder.New()
    .AddDocumentFromString("type Query { products: [Product] }")
    .AddType()
    .Create();

ISchema orderSchema = SchemaBuilder.New()
    .AddDocumentFromString("type Query { orders: [Order] }")
    .AddType()
    .Create();

// Stitch schemas
ISchema stitchedSchema = new StitchedSchema(
    new StitchedSchema.StitchedSchemaConfiguration
    {
        Queries = new[] { productSchema.Query, orderSchema.Query },
        Types = new[] { productSchema.Types, orderSchema.Types }
    });

// Create GraphQL server with stitched schema
var server = new GraphQLServer(stitchedSchema);