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name aspnet-core-fundamentals version 2.0.0 description Master ASP.NET Core fundamentals including C#, project structure, routing, middleware, and basic API development. Essential skills for all ASP.NET Core developers. sasmp_version 1.3.0 bonded_agent aspnet-core-backend bond_type PRIMARY_BOND skill_type atomic responsibility single parameters {"dotnet_version":{"type":"string","required":false,"default":"9.0","validation":{"pattern":"^[6-9]\\.0$","allowed_values":["6.0","7.0","8.0","9.0"]}},"project_type":{"type":"string","required":false,"default":"webapi","validation":{"allowed_values":["webapi","mvc","razor","minimal"]}},"database_provider":{"type":"string","required":false,"default":"sqlserver","validation":{"allowed_values":["sqlserver","postgresql","mysql","sqlite","inmemory"]}}} retry_config {"enabled":true,"max_attempts":3,"backoff_type":"exponential","initial_delay_ms":1000,"max_delay_ms":10000,"jitter":true,"retryable_errors":["NETWORK_ERROR","TIMEOUT","RATE_LIMIT"]} observability {"logging":{"enabled":true,"level":"Information","include_parameters":true,"sensitive_fields":["connectionString","password","apiKey"]},"metrics":{"enabled":true,"namespace":"skill.aspnetcore.fundamentals","dimensions":["operation","status","duration_bucket"]},"tracing":{"enabled":true,"span_name":"aspnetcore-fundamentals","attributes":["skill.version","skill.operation","user.intent"]}} test_templates {"framework":"xunit","mocking":"moq","assertions":"fluent_assertions","coverage_target":80}
ASP.NET Core Fundamentals
Skill Overview
Production-grade fundamentals skill for ASP.NET Core 8.0/9.0 development. Implements atomic, single-responsibility design with comprehensive validation, retry logic, and observability.
Core Skills
C# Essentials (C# 12/13)
fundamentals:
variables_and_types:
- Primitive types (int, string, bool, decimal)
- Reference vs value types
- Nullable reference types (NRT)
- var and target-typed new
- Records and record structs
control_flow:
- if/else, switch expressions
- Pattern matching
- for, foreach, while loops
- LINQ query syntax
- Exception handling (try/catch/finally)
functions_and_methods:
-
Method
signatures
and
overloading
-
Optional
and
named
parameters
-
ref,
out,
in
parameters
-
Local
functions
-
Expression-bodied
members
oop_principles:
-
Classes
and
inheritance
-
Interfaces
and
abstract
classes
-
Encapsulation
(access
modifiers)
-
Polymorphism
-
Composition
over
inheritance
modern_csharp:
-
Primary
constructors
(C#
12
)
-
Collection
expressions
(C#
12
)
-
Raw
string
literals
-
Required
members
-
File-scoped
types
async_programming:
-
async/await
fundamentals
-
Task
and
ValueTask
-
Cancellation
tokens
-
Async
streams
(IAsyncEnumerable)
-
ConfigureAwait
considerations
ASP.NET Core Project Setup project_creation:
commands:
webapi: dotnet new webapi -n MyApi --use-controllers
minimal_api: dotnet new webapi -n MyApi
mvc: dotnet new mvc -n MyApp
razor: dotnet new razor -n MyApp
project_structure:
root:
- Program.cs (entry point, DI, middleware)
- appsettings.json (configuration)
- appsettings.Development.json
controllers:
- Controller classes
models:
- Entity classes
- DTOs
services:
- Business logic
data:
- DbContext
- Repositories
configuration:
appsettings_structure:
ConnectionStrings: Database connections
Logging: Log level configuration
AllowedHosts: CORS settings
CustomSettings: Application-specific
environment_variables:
ASPNETCORE_ENVIRONMENT: Development/Staging/Production
ASPNETCORE_URLS: Binding URLs
configuration_sources:
- appsettings.json
- appsettings.{Environment}.json
- Environment variables
- User secrets (development)
- Azure Key Vault (production)
Routing & Controllers attribute_routing:
controller_level: "[Route(\"api/[controller]\")]"
action_level: "[HttpGet(\"{id}\")]"
route_constraints:
- "{id:int}" (integer)
- "{name:alpha}" (letters only)
- "{date:datetime}" (date)
- "{id:min(1)}" (minimum value)
http_methods:
- "[HttpGet]" - Retrieve resource
- "[HttpPost]" - Create resource
- "[HttpPut]" - Replace resource
- "[HttpPatch]" - Partial update
- "[HttpDelete]" - Remove resource
action_results:
success:
- Ok(data) - 200
- Created(uri, data) - 201
- NoContent() - 204
- Accepted() - 202
client_errors:
- BadRequest(error) - 400
- Unauthorized() - 401
- Forbidden() - 403
- NotFound() - 404
- Conflict() - 409
server_errors:
- StatusCode(500) - Internal error
model_binding:
sources:
- "[FromRoute]" - URL path
- "[FromQuery]" - Query string
- "[FromBody]" - Request body (JSON)
- "[FromHeader]" - HTTP headers
- "[FromForm]" - Form data
- "[FromServices]" - DI container
Middleware Pipeline middleware_order:
1: Exception handling
2: HTTPS redirection
3: Static files
4: Routing
5: CORS
6: Authentication
7: Authorization
8: Custom middleware
9: Endpoints
built_in_middleware:
- UseExceptionHandler()
- UseHttpsRedirection()
- UseStaticFiles() / MapStaticAssets() (.NET 9 )
- UseRouting()
- UseCors()
- UseAuthentication()
- UseAuthorization()
- UseRateLimiter()
custom_middleware:
inline: app.Use(async (context, next) => { ... })
class_based: app.UseMiddleware<CustomMiddleware>()
convention: Must have Invoke/InvokeAsync method
Models & Data Binding model_classes:
entities:
purpose: Database representation
features:
- Navigation properties
- Data annotations
- Fluent configuration
dtos:
purpose: API contracts
best_practices:
- Separate from entities
- Use records for immutability
- Include only needed fields
validation:
data_annotations:
- "[Required]"
- "[StringLength(100)]"
- "[Range(1, 100)]"
- "[EmailAddress]"
- "[RegularExpression(pattern)]"
- "[Compare(\"OtherProperty\")]"
fluent_validation:
purpose: Complex validation rules
example: |
RuleFor(x => x.Email)
.NotEmpty()
.EmailAddress()
.Must(BeUniqueEmail);
model_binding_validation:
automatic: ModelState.IsValid
problem_details: Automatic 400 response
custom_response: Override with filters
Dependency Injection service_lifetimes:
singleton:
description: Single instance for application lifetime
use_cases:
- Configuration
- Caching services
- Logging
caution: Thread-safety required
scoped:
description: New instance per request
use_cases:
- DbContext
- Request-specific services
- Unit of Work
transient:
description: New instance every time
use_cases:
- Lightweight stateless services
- Factory-created services
caution: Memory allocation overhead
registration_patterns:
interface_based: |
services.AddScoped<IProductService, ProductService>();
concrete_type: |
services.AddSingleton<MyConfiguration>();
factory: |
services.AddScoped<IService>(sp =>
new MyService(sp.GetRequiredService<IDependency>()));
keyed_services: |
services.AddKeyedSingleton<ICache>("memory", new MemoryCache());
services.AddKeyedSingleton<ICache>("redis", new RedisCache());
Code Examples
Production-Ready Minimal API var builder = WebApplication.CreateBuilder(args );
builder.Configuration
.AddJsonFile("appsettings.json" , optional: false )
.AddJsonFile($"appsettings.{builder.Environment.EnvironmentName} .json" , optional: true )
.AddEnvironmentVariables();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddScoped<IProductService, ProductService>();
builder.Services.AddDbContext<AppDbContext>(options =>
options.UseSqlServer(builder.Configuration.GetConnectionString("Default" )));
builder.Services.AddValidatorsFromAssemblyContaining<Program>();
builder.Services.AddProblemDetails();
var app = builder.Build();
if (app.Environment.IsDevelopment())
{
app.UseSwagger();
app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.UseExceptionHandler();
var products = app.MapGroup("/api/products" )
.WithTags("Products" )
.WithOpenApi();
products.MapGet("/" , async (IProductService service, CancellationToken ct) =>
{
var result = await service.GetAllAsync(ct);
return Results.Ok(result);
})
.WithName("GetProducts" )
.Produces<IEnumerable<ProductDto>>(StatusCodes.Status200OK);
products.MapGet("/{id:int}" , async (int id, IProductService service, CancellationToken ct) =>
{
var product = await service.GetByIdAsync(id, ct);
return product is null
? Results.NotFound()
: Results.Ok(product);
})
.WithName("GetProduct" )
.Produces<ProductDto>(StatusCodes.Status200OK)
.Produces(StatusCodes.Status404NotFound);
products.MapPost("/" , async (
CreateProductRequest request,
IValidator<CreateProductRequest> validator,
IProductService service,
CancellationToken ct) =>
{
var validation = await validator.ValidateAsync(request, ct);
if (!validation.IsValid)
return Results.ValidationProblem(validation.ToDictionary());
var id = await service.CreateAsync(request, ct);
return Results.Created($"/api/products/{id} " , new { id });
})
.WithName("CreateProduct" )
.Produces<object >(StatusCodes.Status201Created)
.ProducesValidationProblem();
app.Run();
Controller-Based API [ApiController ]
[Route("api/[controller]" ) ]
[Produces("application/json" ) ]
public class ProductsController : ControllerBase
{
private readonly IProductService _service;
private readonly ILogger<ProductsController> _logger;
public ProductsController (
IProductService service,
ILogger<ProductsController> logger )HttpGet ]
[ProducesResponseType(typeof(PagedResult<ProductDto>), StatusCodes.Status200OK) ]
public async Task<ActionResult<PagedResult<ProductDto>>> GetProducts(
[FromQuery ] ProductQueryParameters query,
CancellationToken ct)
{
var result = await _service.GetProductsAsync(query, ct);
Response.Headers.Append("X-Total-Count" , result.TotalCount.ToString());
return Ok(result);
}
[HttpGet("{id:int}" ) ]
[ProducesResponseType(typeof(ProductDto), StatusCodes.Status200OK) ]
[ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status404NotFound) ]
public async Task<ActionResult<ProductDto>> GetProduct(
int id,
CancellationToken ct)
{
var product = await _service.GetByIdAsync(id, ct);
if (product is null )
{
_logger.LogWarning("Product {ProductId} not found" , id);
return NotFound();
}
return Ok(product);
}
[HttpPost ]
[ProducesResponseType(typeof(ProductDto), StatusCodes.Status201Created) ]
[ProducesResponseType(typeof(ValidationProblemDetails), StatusCodes.Status400BadRequest) ]
public async Task<ActionResult<ProductDto>> CreateProduct(
[FromBody ] CreateProductRequest request,
CancellationToken ct)
{
var product = await _service.CreateAsync(request, ct);
return CreatedAtAction(
nameof (GetProduct),
new { id = product.Id },
product);
}
[HttpPut("{id:int}" ) ]
[ProducesResponseType(StatusCodes.Status204NoContent) ]
[ProducesResponseType(StatusCodes.Status404NotFound) ]
public async Task<IActionResult> UpdateProduct (
int id,
[FromBody] UpdateProductRequest request,
CancellationToken ct )var success = await _service.UpdateAsync(id, request, ct);
if (!success)
return NotFound();
return NoContent();
}
[HttpDelete("{id:int}" ) ]
[ProducesResponseType(StatusCodes.Status204NoContent) ]
[ProducesResponseType(StatusCodes.Status404NotFound) ]
public async Task<IActionResult> DeleteProduct (int id, CancellationToken ctvar success = await _service.DeleteAsync(id, ct);
if (!success)
return NotFound();
return NoContent();
}
}
Custom Middleware public class RequestLoggingMiddleware
{
private readonly RequestDelegate _next;
private readonly ILogger<RequestLoggingMiddleware> _logger;
public RequestLoggingMiddleware (
RequestDelegate next,
ILogger<RequestLoggingMiddleware> logger )public async Task InvokeAsync (HttpContext context )var correlationId = context.Request.Headers["X-Correlation-ID" ].FirstOrDefault()
?? Guid.NewGuid().ToString();
context.Response.Headers.Append("X-Correlation-ID" , correlationId);
using var scope = _logger.BeginScope(new Dictionary<string , object >
{
["CorrelationId" ] = correlationId,
["RequestPath" ] = context.Request.Path,
["RequestMethod" ] = context.Request.Method
});
var stopwatch = Stopwatch.StartNew();
try
{
await _next(context);
}
finally
{
stopwatch.Stop();
_logger.LogInformation(
"{Method} {Path} completed in {ElapsedMs}ms with status {StatusCode}" ,
context.Request.Method,
context.Request.Path,
stopwatch.ElapsedMilliseconds,
context.Response.StatusCode);
}
}
}
app.UseMiddleware<RequestLoggingMiddleware>();
Configuration with Options Pattern
{
"EmailSettings" : {
"SmtpServer" : "smtp.example.com" ,
"SmtpPort" : 587 ,
"SenderEmail" : "noreply@example.com" ,
"EnableSsl" : true
}
}
public class EmailSettings
{
public const string SectionName = "EmailSettings" ;
public string SmtpServer { get ; init ; } = string .Empty;
public int SmtpPort { get ; init ; } = 587 ;
public string SenderEmail { get ; init ; } = string .Empty;
public bool EnableSsl { get ; init ; } = true ;
}
builder.Services.AddOptions<EmailSettings>()
.BindConfiguration(EmailSettings.SectionName)
.ValidateDataAnnotations()
.ValidateOnStart();
public class EmailService
{
private readonly EmailSettings _settings;
public EmailService (IOptions<EmailSettings> options )public class EmailService
{
private readonly IOptionsSnapshot<EmailSettings> _options;
public EmailSettings Settings => _options.Value;
}
Unit Test Templates
Controller Unit Test public class ProductsControllerTests
{
private readonly Mock<IProductService> _serviceMock;
private readonly Mock<ILogger<ProductsController>> _loggerMock;
private readonly ProductsController _controller;
public ProductsControllerTests ()new Mock<IProductService>();
_loggerMock = new Mock<ILogger<ProductsController>>();
_controller = new ProductsController(_serviceMock.Object, _loggerMock.Object);
}
[Fact ]
public async Task GetProduct_WhenExists_ReturnsOk ()var productId = 1 ;
var expectedProduct = new ProductDto { Id = productId, Name = "Test" };
_serviceMock
.Setup(s => s.GetByIdAsync(productId, It.IsAny<CancellationToken>()))
.ReturnsAsync(expectedProduct);
var result = await _controller.GetProduct(productId, CancellationToken.None);
var okResult = result.Result.Should().BeOfType<OkObjectResult>().Subject;
var product = okResult.Value.Should().BeOfType<ProductDto>().Subject;
product.Id.Should().Be(productId);
}
[Fact ]
public async Task GetProduct_WhenNotFound_ReturnsNotFound ()var productId = 999 ;
_serviceMock
.Setup(s => s.GetByIdAsync(productId, It.IsAny<CancellationToken>()))
.ReturnsAsync((ProductDto?)null );
var result = await _controller.GetProduct(productId, CancellationToken.None);
result.Result.Should().BeOfType<NotFoundResult>();
}
[Fact ]
public async Task CreateProduct_WithValidData_ReturnsCreated ()var request = new CreateProductRequest { Name = "New Product" , Price = 99.99 m };
var createdProduct = new ProductDto { Id = 1 , Name = request.Name, Price = request.Price };
_serviceMock
.Setup(s => s.CreateAsync(request, It.IsAny<CancellationToken>()))
.ReturnsAsync(createdProduct);
var result = await _controller.CreateProduct(request, CancellationToken.None);
var createdResult = result.Result.Should().BeOfType<CreatedAtActionResult>().Subject;
createdResult.ActionName.Should().Be(nameof (ProductsController.GetProduct));
createdResult.RouteValues!["id" ].Should().Be(1 );
}
}
Integration Test public class ProductsApiTests : IClassFixture <WebApplicationFactory <Program >>
{
private readonly HttpClient _client;
private readonly WebApplicationFactory<Program> _factory;
public ProductsApiTests (WebApplicationFactory<Program> factory )"TestDb" ));
});
});
_client = _factory.CreateClient();
}
[Fact ]
public async Task GetProducts_ReturnsSuccessStatusCode ()var response = await _client.GetAsync("/api/products" );
response.StatusCode.Should().Be(HttpStatusCode.OK);
}
[Fact ]
public async Task CreateProduct_WithValidData_ReturnsCreated ()var request = new { Name = "Test Product" , Price = 99.99 };
var content = new StringContent(
JsonSerializer.Serialize(request),
Encoding.UTF8,
"application/json" );
var response = await _client.PostAsync("/api/products" , content);
response.StatusCode.Should().Be(HttpStatusCode.Created);
response.Headers.Location.Should().NotBeNull();
}
[Fact ]
public async Task CreateProduct_WithInvalidData_ReturnsBadRequest ()var request = new { Name = "" , Price = -1 };
var content = new StringContent(
JsonSerializer.Serialize(request),
Encoding.UTF8,
"application/json" );
var response = await _client.PostAsync("/api/products" , content);
response.StatusCode.Should().Be(HttpStatusCode.BadRequest);
}
}
Troubleshooting Guide
Common Issues Issue Symptoms Resolution 404 Not Found Route not matching Check route template, HTTP method 415 Unsupported Media Type Content-Type missing Add Content-Type: application/json 500 Internal Error Unhandled exception Check logs, add exception middleware Model binding fails Null values Check property names, [FromBody] attribute DI resolution fails Service not registered Add service to DI container
Debug Checklist step_1_routing:
- Verify controller has [ApiController ] attribute
- Check route template matches URL
- Confirm HTTP method matches action attribute
- Validate route constraints
step_2_model_binding:
- Check JSON property names match
- Verify Content-Type header
- Inspect ModelState errors
- Check for [FromBody ], [FromQuery ] attributes
step_3_di_issues:
- Verify service is registered
- Check service lifetime compatibility
- Look for circular dependencies
- Inspect exception details
step_4_configuration:
- Verify appsettings.json syntax
- Check environment name
- Confirm configuration binding
- Inspect IConfiguration values
Assessment Criteria
References 