C#.NET - day 10

Day 10: Structuring and Circulating Data (DTO & Read Flow)

From unstructured input to a complete data lifecycle

Introduction

At this stage, the system starts to feel different. Until now, data was created in a somewhat direct way.

With Day 10, the flow becomes explicit and structured:

input → mapping → storage → retrieval

This is the point where the system begins to resemble a real production pipeline, rather than a simple request-response experiment.

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🔄 Updated System Flow

1. Input (Day 10 – DTO): The user submits a structured request (JSON) containing a name and a message.
2. Packaging (Mapping): The system converts the request into a database-ready entity.
3. Storage (DB): The data is persisted in the database.
4. Retrieval (Day 10 – GET): The user requests the full list, and the system returns all stored records.

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1️⃣ Input Model: HelloRequest (DTO)

This class acts as a delivery box. Instead of accepting loose values, the system now requires a defined structure.

namespace HelloFlow.Models
{
    // Data Transfer Object (DTO)
    // Used only for incoming requests from the client.
    public class HelloRequest
    {
        public string Name { get; set; }
        public string Message { get; set; }
    }
}

By introducing a DTO, the server gains control over what input is allowed.

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2️⃣ Controller: Orchestrating Write and Read (Day 10)

The Controller now acts as a logistics center. It accepts incoming packages, stores them, and later retrieves them.

using Microsoft.AspNetCore.Mvc;
using HelloFlow.Data;
using HelloFlow.Models;

namespace HelloFlow.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class HelloController : ControllerBase
    {
        private readonly AppDbContext _context;

        public HelloController(AppDbContext context)
        {
            _context = context;
        }

        // ==========================================
        // Day 10: Read (GET)
        // ==========================================
        [HttpGet]
        public IActionResult GetAllMessages()
        {
            var messages = _context.HelloResponses.ToList();
            return Ok(messages);
        }

        // ==========================================
        // Day 10: Write (POST)
        // ==========================================
        [HttpPost]
        public IActionResult CreateHello([FromBody] HelloRequest request)
        {
            if (request == null || string.IsNullOrEmpty(request.Message))
            {
                return BadRequest("Message content is missing.");
            }

            // Mapping: DTO → Entity
            var newResponse = new HelloResponse
            {
                Message = $"[{request.Name}] {request.Message}",
                CreatedAt = DateTime.UtcNow
            };

            _context.HelloResponses.Add(newResponse);
            _context.SaveChanges();

            return Ok(newResponse);
        }
    }
}

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🚀 Local Testing Guide (Rider)

1️⃣ Writing Data (POST)

Use Swagger and send the following request body:

{
  "name": "Sabin",
  "message": "Now I am sending structured data."
}

Confirm that the response status is 200 OK.

2️⃣ Reading Data (GET)

Call GET /api/Hello and confirm that all previously stored entries are returned as a list.

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🧠 What Changed on Day 10

• Input is no longer free-form; it must follow a defined structure (DTO).
• Data flows in a full cycle: request → database → response.
• The system feels less like a collection of endpoints and more like a coherent pipeline.

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🧠 One-Sentence Summary

Day 10 completes the data loop by introducing structured input and consistent retrieval.

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✍️ My Notes & Reflections

• As more components are added, the system becomes more complex, but it also feels more organized.
• I am starting to understand how a single factory slowly comes together, with data flowing through clearly defined stages.