Controllers and Routing

Level: Intermediate

ℹ️ What You'll Learn

• Controller purpose: Organize related endpoints (StudentsController for student endpoints, TeachersController for teacher endpoints)
• [ApiController] attribute: Auto-validates input, returns 400 Bad Request if validation fails, returns problem details on error
• ControllerBase: Base class for API controllers (JSON responses, no View support)
• [Route("api/[controller]")]: Base route for all actions in controller (StudentsController → api/students)
• [HttpGet]: Handle GET requests (read data, safe, idempotent)
• [HttpPost]: Handle POST requests (create new resource)
• HttpPut: Handle PUT requests (update entire resource by ID)
• HttpDelete: Handle DELETE requests (delete resource by ID)
• Route parameters: HttpGet captures id from URL path for resource identification
• Route constraints: Constrain parameters to specific types (int, guid) for validation
• [FromRoute]: Explicit binding from URL parameter (usually not needed, inferred from parameter name)
• [FromQuery]: Binding from query string (?className=10A → className parameter)
• [FromBody]: Binding from request body (POST/PUT with JSON → Student object)
• API versioning: [Route("api/v1/[controller]")] for version 1, api/v2/[controller] for version 2
• School Management controller structure: StudentsController, TeachersController, ExamsController, FeesController, AttendanceController
• Action naming: GetStudents (GET all), GetStudent (GET by ID), CreateStudent (POST), UpdateStudent (PUT), DeleteStudent (DELETE)

Controller Basics

File: Controllers/StudentsController.cs

[ApiController]
[Route("api/[controller]")]
public class StudentsController : ControllerBase
{
    // Actions here
}

[ApiController] = automatic model validation, problem details response. [Route("api/[controller]")] = base route /api/students

Route Definition

[HttpGet]                    // GET /api/students
public async Task<ActionResult<List<Student>>> GetStudents()

[HttpGet("{id}")]            // GET /api/students/101
public async Task<ActionResult<Student>> GetStudent(int id)

[HttpPost]                   // POST /api/students
public async Task<ActionResult<Student>> CreateStudent([FromBody] Student student)

[HttpPut("{id}")]            // PUT /api/students/101
public async Task<ActionResult> UpdateStudent(int id, [FromBody] Student student)

[HttpDelete("{id}")]         // DELETE /api/students/101
public async Task<ActionResult> DeleteStudent(int id)

Route Constraints

[HttpGet("{id:int}")]        // id must be integer
[HttpGet("{id:guid}")]       // id must be GUID
[HttpGet("{id:min(1)}")]     // id >= 1
[HttpGet("search/{query}")]  // exact match

Multiple Controllers

SMS API structure:

// StudentsController
[Route("api/[controller]")]
public class StudentsController : ControllerBase

// ExamsController
[Route("api/[controller]")]
public class ExamsController : ControllerBase

// FeesController
[Route("api/[controller]")]
public class FeesController : ControllerBase

Routes:

• /api/students
• /api/exams
• /api/fees

Custom Routes

[Route("api/student")]
public class StudentController : ControllerBase
{
    [HttpGet("active")]
    public async Task<ActionResult<List<Student>>> GetActiveStudents()
    {
        // GET /api/student/active
    }

    [HttpGet("class/{className}")]
    public async Task<ActionResult<List<Student>>> GetByClass(string className)
    {
        // GET /api/student/class/10-A
    }
}

Route Order

Routes evaluated top-to-bottom:

[HttpGet("{id:int}")]        // Specific routes first
public async Task<ActionResult<Student>> GetStudent(int id)

[HttpGet("{name}")]          // General routes last
public async Task<ActionResult<Student>> GetStudentByName(string name)

Key Takeaways

• Controller = organize related endpoints
• Route = URL path
• Constraints = validate route parameters
• Attribute routing = flexible, explicit

💡 Routing Tip

Keep routes simple and RESTful. /api/students/{id} not /api/get-student-by-id.

🤖Use AI to Learn Faster

Use ChatGPT, Claude, or Copilot to go deeper on Controllers and Routing. Try these prompts:

• "What's the purpose of [ApiController]?"
• "How do I use route constraints?"
• "When should I create new controllers?"
• "Quiz me on routing"

💡 Tip: After reading this article, paste your own code into AI and ask "What could go wrong here and why?" — fastest way to find edge cases and deepen understanding.