Sınıflara ait dersleri atama işlemini ve CRUD işlemlerini gerçekleştirebiliriz. Aşağıda DersAra için gerekli adımlar ve dosya yapısı yer alıyor.

Controllers/Admin/DersAraController.cs dosyasını oluşturarak CRUD işlemlerini gerçekleştirelim.

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using SchoolManagement.Data;
using SchoolManagement.Models;

namespace SchoolManagement.Controllers.Admin
{
    //[Area("Admin")]
    [Authorize(Roles = "Admin")] // Sadece admin kullanıcıları erişebilecek
    public class DersAraController : Controller
    {
        private readonly ApplicationDbContext _context;

        public DersAraController(ApplicationDbContext context)
        {
            _context = context;
        }

        // GET: Admin/DersAra
        public async Task<IActionResult> Index()
        {
            var dersAra = await _context.DersAralar
                .Include(d => d.Ders)
                .Include(d => d.Sinif)
                .ToListAsync();

            return View("~/Views/Admin/DersAra/Index.cshtml", dersAra);
        }

        // GET: Admin/DersAra/Details/5
        public async Task<IActionResult> Details(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var dersAra = await _context.DersAralar
                .Include(d => d.Ders)
                .Include(d => d.Sinif)
                .FirstOrDefaultAsync(m => m.Id == id);

            if (dersAra == null)
            {
                return NotFound();
            }

            return View("~/Views/Admin/DersAra/Details.cshtml",dersAra);
        }

        // GET: Admin/DersAra/Create
        public IActionResult Create()
        {
            ViewData["DersId"] = new SelectList(_context.Dersler, "Id", "DersAdi");
            ViewData["SinifId"] = new SelectList(_context.Siniflar, "Id", "SinifAdi");
            return View("~/Views/Admin/DersAra/Create.cshtml");
        }

        // POST: Admin/DersAra/Create
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create([Bind("Id,DersId,SinifId")] DersAra dersAra)
        {
            if (!ModelState.IsValid)
            {
                // Check if this course is already assigned to this class
                var exists = await _context.DersAralar
                    .AnyAsync(d => d.DersId == dersAra.DersId && d.SinifId == dersAra.SinifId);

                if (exists)
                {
                    ModelState.AddModelError("", "Bu ders zaten bu sınıfa atanmış.");
                    ViewData["DersId"] = new SelectList(_context.Dersler, "Id", "DersAdi", dersAra.DersId);
                    ViewData["SinifId"] = new SelectList(_context.Siniflar, "Id", "SinifAdi", dersAra.SinifId);
                    return View("~/Views/Admin/DersAra/Create.cshtml", dersAra);
                }

                _context.Add(dersAra);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }

            ViewData["DersId"] = new SelectList(_context.Dersler, "Id", "DersAdi", dersAra.DersId);
            ViewData["SinifId"] = new SelectList(_context.Siniflar, "Id", "SinifAdi", dersAra.SinifId);
            return View("~/Views/Admin/DersAra/Create.cshtml",dersAra);
        }

        // GET: Admin/DersAra/Edit/5
        public async Task<IActionResult> Edit(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var dersAra = await _context.DersAralar.FindAsync(id);
            if (dersAra == null)
            {
                return NotFound();
            }

            ViewData["DersId"] = new SelectList(_context.Dersler, "Id", "DersAdi", dersAra.DersId);
            ViewData["SinifId"] = new SelectList(_context.Siniflar, "Id", "SinifAdi", dersAra.SinifId);
            return View("~/Views/Admin/DersAra/Edit.cshtml",dersAra);
        }

        // POST: Admin/DersAra/Edit/5
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Edit(int id, [Bind("Id,DersId,SinifId")] DersAra dersAra)
        {
            if (id != dersAra.Id)
            {
                return NotFound();
            }

            if (ModelState.IsValid)
            {
                try
                {
                    // Check if this course is already assigned to this class (excluding the current record)
                    var exists = await _context.DersAralar
                        .AnyAsync(d => d.DersId == dersAra.DersId &&
                                   d.SinifId == dersAra.SinifId &&
                                   d.Id != dersAra.Id);

                    if (exists)
                    {
                        ModelState.AddModelError("", "Bu ders zaten bu sınıfa atanmış.");
                        ViewData["DersId"] = new SelectList(_context.Dersler, "Id", "DersAdi", dersAra.DersId);
                        ViewData["SinifId"] = new SelectList(_context.Siniflar, "Id", "SinifAdi", dersAra.SinifId);
                        return View(dersAra);
                    }

                    _context.Update(dersAra);
                    await _context.SaveChangesAsync();
                }
                catch (DbUpdateConcurrencyException)
                {
                    if (!DersAraExists(dersAra.Id))
                    {
                        return NotFound();
                    }
                    else
                    {
                        throw;
                    }
                }
                return RedirectToAction(nameof(Index));
            }

            ViewData["DersId"] = new SelectList(_context.Dersler, "Id", "DersAdi", dersAra.DersId);
            ViewData["SinifId"] = new SelectList(_context.Siniflar, "Id", "SinifAdi", dersAra.SinifId);
            return View("~/Views/Admin/DersAra/Edit.cshtml", dersAra);
        }

        // GET: Admin/DersAra/Delete/5
        public async Task<IActionResult> Delete(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var dersAra = await _context.DersAralar
                .Include(d => d.Ders)
                .Include(d => d.Sinif)
                .FirstOrDefaultAsync(m => m.Id == id);

            if (dersAra == null)
            {
                return NotFound();
            }

            return View("~/Views/Admin/DersAra/Delete.cshtml", dersAra);
        }

        // POST: Admin/DersAra/Delete/5
        [HttpPost, ActionName("Delete")]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> DeleteConfirmed(int id)
        {
            var dersAra = await _context.DersAralar.FindAsync(id);
            _context.DersAralar.Remove(dersAra);
            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }

        private bool DersAraExists(int id)
        {
            return _context.DersAralar.Any(e => e.Id == id);
        }
    }
}

Menüde, Sınıflar ve Dersler için yeni bir buton ekleyelim. Bu buton, DersAraController'ın Index action'ına yönlendirecek.

<!-- Atama İşlemleri Dropdown Menüsü -->
<li class="nav-item dropdown">
    <a class="nav-link dropdown-toggle" href="#" id="atamaDropdown" role="button" data-bs-toggle="dropdown" aria-expanded="false">
        Atama İşlemleri
    </a>
    <ul class="dropdown-menu" aria-labelledby="atamaDropdown">
        <li><a class="dropdown-item" asp-controller="DersAra" asp-action="Index">Sınıf ve Dersler</a></li>
    </ul>
</li>

Sınıf ve derslerin listeleneceği ana sayfayı Views/Admin/DersAra/Index.cshtml dosyasına ekleyelim.

@model IEnumerable<SchoolManagement.Models.DersAra>

@{
    ViewData["Title"] = "Sınıf-Ders Atamaları";
}

<h1>Sınıf-Ders Atamaları</h1>

<p>
    <a asp-action="Create" class="btn btn-primary">Yeni Atama</a>
</p>
<table class="table table-striped table-bordered">
    <thead>
        <tr>
            <th>
                Sınıf
            </th>
            <th>
                Ders
            </th>
            <th>İşlemler</th>
        </tr>
    </thead>
    <tbody>
        @foreach (var item in Model)
        {
            <tr>
                <td>
                    @Html.DisplayFor(modelItem => item.Sinif.SinifAdi)
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.Ders.DersAdi)
                </td>
                <td>
                    <a asp-action="Edit" asp-route-id="@item.Id" class="btn btn-sm btn-warning">Düzenle</a> |
                    <a asp-action="Details" asp-route-id="@item.Id" class="btn btn-sm btn-info">Detaylar</a> |
                    <a asp-action="Delete" asp-route-id="@item.Id" class="btn btn-sm btn-danger">Sil</a>
                </td>
            </tr>
        }
    </tbody>
</table>

Sınıfa yeni Ders eklemek için Views/Admin/DersAra/Create.cshtml dosyasını oluşturacağız.

@model SchoolManagement.Models.DersAra

@{
    ViewData["Title"] = "Yeni Ders Atama";
}

<h1>Yeni Ders Atama</h1>

<hr />
<div class="row">
    <div class="col-md-6">
        <form asp-action="Create">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group mb-3">
                <label asp-for="SinifId" class="control-label">Sınıf</label>
                <select asp-for="SinifId" class="form-control" asp-items="ViewBag.SinifId"></select>
                <span asp-validation-for="SinifId" class="text-danger"></span>
            </div>
            <div class="form-group mb-3">
                <label asp-for="DersId" class="control-label">Ders</label>
                <select asp-for="DersId" class="form-control" asp-items="ViewBag.DersId"></select>
                <span asp-validation-for="DersId" class="text-danger"></span>
            </div>
            <div class="form-group">
                <input type="submit" value="Kaydet" class="btn btn-primary" />
                <a asp-action="Index" class="btn btn-secondary">Listeye Dön</a>
            </div>
        </form>
    </div>
</div>

Eklenen dersi düzenleme işlemi için Views/Admin/DersAra/Edit.cshtml dosyasını ekleyelim.

@model SchoolManagement.Models.DersAra

@{
    ViewData["Title"] = "Ders Atama Düzenle";
}

<h1>Ders Atama Düzenle</h1>

<hr />
<div class="row">
    <div class="col-md-6">
        <form asp-action="Edit">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Id" />
            <div class="form-group mb-3">
                <label asp-for="SinifId" class="control-label">Sınıf</label>
                <select asp-for="SinifId" class="form-control" asp-items="ViewBag.SinifId"></select>
                <span asp-validation-for="SinifId" class="text-danger"></span>
            </div>
            <div class="form-group mb-3">
                <label asp-for="DersId" class="control-label">Ders</label>
                <select asp-for="DersId" class="form-control" asp-items="ViewBag.DersId"></select>
                <span asp-validation-for="DersId" class="text-danger"></span>
            </div>
            <div class="form-group">
                <input type="submit" value="Kaydet" class="btn btn-primary" />
                <a asp-action="Index" class="btn btn-secondary">Listeye Dön</a>
            </div>
        </form>
    </div>
</div>

Sınıfa atanan dersi silme işlemi için Views/Admin/DersAra/Delete.cshtml dosyasını oluşturalım.

@model SchoolManagement.Models.DersAra

@{
    ViewData["Title"] = "Ders Atama Sil";
}

<h1>Ders Atama Sil</h1>

<h3>Bu ders atamasını silmek istediğinize emin misiniz?</h3>
<div>
    <hr />
    <dl class="row">
        <dt class="col-sm-3">Sınıf:</dt>
        <dd class="col-sm-9">@Html.DisplayFor(model => model.Sinif.SinifAdi)</dd>

        <dt class="col-sm-3">Ders:</dt>
        <dd class="col-sm-9">@Html.DisplayFor(model => model.Ders.DersAdi)</dd>
    </dl>

    <form asp-action="Delete">
        <input type="hidden" asp-for="Id" />
        <input type="submit" value="Sil" class="btn btn-danger" /> |
        <a asp-action="Index" class="btn btn-secondary">Listeye Dön</a>
    </form>
</div>