Fix: prevent school subject deletion if they have homework

WorkManagementTool/Components/Homework/HomeworkDeletion.razor

@@ -0,0 +1,21 @@
+@using Microsoft.AspNetCore.Authorization
+@attribute [Authorize]
+@using WorkManagementTool.Services
+@using WorkManagementTool.Data.Entities
+@inject HomeworkService HomeworkService
+
+<button class="btn btn-danger">-</button>
+
+@code {
+    [Parameter]
+    public int HomeworkId { get; set; }
+
+    [Parameter]
+    public EventCallback<int> OnDeleted { get; set; }
+
+    private async Task Delete(MouseEventArgs e)
+    {
+        await HomeworkService.DeleteHomeworkAsync(HomeworkId);
+        await OnDeleted.InvokeAsync(HomeworkId);
+    }
+}

WorkManagementTool/Components/SchoolSubject/SchoolSubjectDeletion.razor

@@ -5,7 +5,10 @@
 @using WorkManagementTool.Services
 @inject SchoolSubjectService SchoolSubjectService
 
-<button type="button" class="btn btn-danger" @onclick="Delete">-</button>
+@if (!hasHomeworks)
+{
+    <button type="button" class="btn btn-danger" @onclick="Delete">-</button>
+}
 
 @code {
     [Parameter]
@@ -14,6 +17,16 @@
     [Parameter]
     public EventCallback<int> OnDeleted { get; set; }
 
+    private bool hasHomeworks;
+
+    protected override async Task OnInitializedAsync()
+    {
+        var schoolSubject = await SchoolSubjectService.GetSchoolSubjectByIdAsync(Id);
+
+        hasHomeworks = schoolSubject is not null
+            && schoolSubject.Homeworks?.Count > 0;
+    }
+
     private async Task Delete(MouseEventArgs e)
     {
         await SchoolSubjectService.DeleteSchoolSubjectAsync(Id);

WorkManagementTool/Data/Entities/SchoolSubject.cs

@@ -13,5 +13,6 @@ namespace WorkManagementTool.Data.Entities
         public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
         public bool Deleted { get; set; } = false;
         public ApplicationUser CreatedBy { get; set; } = null!;
+        public List<Homework>? Homeworks { get; set; }
     }
 }

WorkManagementTool/Services/SchoolSubjectService.cs

@@ -20,7 +20,10 @@ namespace WorkManagementTool.Services
 
         public async Task<SchoolSubject?> GetSchoolSubjectByIdAsync(int id)
         {
-            return await _context.SchoolSubjects.FindAsync(id);
+            return await _context.SchoolSubjects
+                .Include(i => i.Homeworks)
+                .Where(w => w.Id == id)
+                .FirstOrDefaultAsync();
         }
 
         public async Task AddSchoolSubjectAsync(SchoolSubject subject)