Routing and Controllers

1[ApiController]
2[Route("api/[controller]")]  // api/products
3public class ProductsController : ControllerBase
4{
5    // GET api/products
6    [HttpGet]
7    public IActionResult GetAll() => Ok(products);
8
9    // GET api/products/5
10    [HttpGet("{id}")]
11    public IActionResult GetById(int id) => Ok(product);
12
13    // GET api/products/5/reviews
14    [HttpGet("{id}/reviews")]
15    public IActionResult GetReviews(int id) => Ok(reviews);
16
17    // POST api/products
18    [HttpPost]
19    public IActionResult Create([FromBody] ProductDto dto) => Created(...);
20
21    // PUT api/products/5
22    [HttpPut("{id}")]
23    public IActionResult Update(int id, [FromBody] ProductDto dto) => Ok(updated);
24
25    // DELETE api/products/5
26    [HttpDelete("{id}")]
27    public IActionResult Delete(int id) => NoContent();
28}
29
30// Route constraints
31[HttpGet("{id:int}")]              // Only integers
32[HttpGet("{name:alpha}")]          // Only letters
33[HttpGet("{slug:regex(^[a-z]+$)}")] // Regex match
34[HttpGet("{date:datetime}")]       // Valid DateTime
35[HttpGet("{id:min(1):max(100)}")]  // Range constraint

1[ApiController]
2[Route("api/[controller]")]
3[Produces("application/json")]
4public class UsersController : ControllerBase
5{
6    private readonly IUserService _userService;
7    private readonly ILogger<UsersController> _logger;
8
9    public UsersController(IUserService userService, ILogger<UsersController> logger)
10    {
11        _userService = userService;
12        _logger = logger;
13    }
14
15    [HttpGet]
16    [ProducesResponseType(typeof(IEnumerable<UserDto>), 200)]
17    public async Task<IActionResult> GetAll([FromQuery] int page = 1, [FromQuery] int pageSize = 10)
18    {
19        var users = await _userService.GetAllAsync(page, pageSize);
20        return Ok(users);
21    }
22
23    [HttpGet("{id}")]
24    [ProducesResponseType(typeof(UserDto), 200)]
25    [ProducesResponseType(404)]
26    public async Task<IActionResult> GetById(int id)
27    {
28        var user = await _userService.GetByIdAsync(id);
29        if (user == null) return NotFound();
30        return Ok(user);
31    }
32
33    [HttpPost]
34    [ProducesResponseType(typeof(UserDto), 201)]
35    [ProducesResponseType(400)]
36    public async Task<IActionResult> Create([FromBody] CreateUserDto dto)
37    {
38        var user = await _userService.CreateAsync(dto);
39        return CreatedAtAction(nameof(GetById), new { id = user.Id }, user);
40    }
41}

1// Model binding sources
2[HttpGet("{id}")]
3public IActionResult Get(
4    [FromRoute] int id,           // From URL path
5    [FromQuery] string filter,    // From query string
6    [FromHeader] string apiKey,   // From request headers
7    [FromBody] RequestDto body,   // From request body
8    [FromServices] IMyService svc // From DI container
9) { }
10
11// Example: GET /api/products/5?category=electronics
12// Header: X-Api-Key: abc123
13[HttpGet("{id}")]
14public IActionResult GetProduct(
15    [FromRoute] int id,
16    [FromQuery] string category,
17    [FromHeader(Name = "X-Api-Key")] string apiKey)
18{
19    // id = 5
20    // category = "electronics"
21    // apiKey = "abc123"
22}
23
24// Complex query parameters
25public record ProductQuery(
26    string? Search,
27    string? Category,
28    decimal? MinPrice,
29    decimal? MaxPrice,
30    int Page = 1,
31    int PageSize = 20
32);
33
34[HttpGet]
35public IActionResult Search([FromQuery] ProductQuery query)
36{
37    // Automatically binds all query params to record
38}
39
40// Custom model binder
41public class CommaSeparatedModelBinder : IModelBinder
42{
43    public Task BindModelAsync(ModelBindingContext context)
44    {
45        var value = context.ValueProvider.GetValue(context.ModelName).FirstValue;
46        var result = value?.Split(',').Select(int.Parse).ToList();
47        context.Result = ModelBindingResult.Success(result);
48        return Task.CompletedTask;
49    }
50}

1// Common action results
2[HttpGet]
3public IActionResult GetExample()
4{
5    // Success responses
6    return Ok(data);                    // 200 OK with body
7    return Created("/url", data);       // 201 Created
8    return CreatedAtAction("Get", new { id = 1 }, data);
9    return NoContent();                 // 204 No Content
10    return Accepted();                  // 202 Accepted
11
12    // Client error responses
13    return BadRequest("Invalid input"); // 400 Bad Request
14    return BadRequest(ModelState);      // 400 with validation errors
15    return Unauthorized();              // 401 Unauthorized
16    return Forbid();                    // 403 Forbidden
17    return NotFound();                  // 404 Not Found
18    return Conflict("Already exists");  // 409 Conflict
19
20    // Server errors
21    return StatusCode(500, "Error");    // 500 Internal Error
22
23    // Redirects
24    return RedirectToAction("Index");
25    return RedirectToRoute("routeName");
26
27    // Files
28    return File(bytes, "application/pdf", "file.pdf");
29    return PhysicalFile("/path/file.pdf", "application/pdf");
30}
31
32// Typed results with ActionResult<T>
33[HttpGet("{id}")]
34public async Task<ActionResult<ProductDto>> GetById(int id)
35{
36    var product = await _repo.GetByIdAsync(id);
37    if (product == null) return NotFound();
38    return product;  // Implicitly Ok(product)
39}