【C#、Blazor】Webアプリ開発入門編（6）「Todoアプリ」へユーザ認証・管理機能をつける ～ASP.NET Core Identityの使い方～

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using TodoListApp.Data;

namespace TodoListApp.Models;

public class TodoItem
{
    [Key]
    public int Id { get; set; }
    public string Title { get; set; } = string.Empty;
    [ForeignKey(nameof(ApplicationUser))]
    public string UserId { get; set; } = string.Empty;
}

dotnet ef migrations add AddForeignKeyToTodoItem -o Data\Migrations

dotnet ef database update

using Microsoft.EntityFrameworkCore;
using TodoListApp.Data;
using TodoListApp.Models;

namespace TodoListApp.Services;

public class TodoListService
{
    private readonly ApplicationDbContext _context;

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

    public async Task<List<TodoItem>> GetTodosAsync(string userId)
    {
        var items = await _context.TodoItems.Where(t => t.UserId == userId).ToListAsync();
        return items;
    }

    public async Task UpdateTodoAsync(string userId, TodoItem todoItemInput)
    {
        var existingTodoItem = await _context.TodoItems.FindAsync(todoItemInput.Id);
        if (existingTodoItem != null && existingTodoItem.UserId == userId)
        {
            existingTodoItem.Title = todoItemInput.Title;
            await _context.SaveChangesAsync();
        }
    }

    public async Task DeleteTodoAsync(string userId, int todoId)
    {
        var existingTodoItem = await _context.TodoItems.FindAsync(todoId);
        if (existingTodoItem != null && existingTodoItem.UserId == userId)
        {
            _context.TodoItems.Remove(existingTodoItem);
            await _context.SaveChangesAsync();
        }
    }

    public async Task AddTodoAsync(string userId, TodoItem newTodoItem)
    {
        newTodoItem.UserId = userId;
        _context.TodoItems.Add(newTodoItem);
        await _context.SaveChangesAsync();
    }
}

@page "/todolist"
@rendermode InteractiveServer
@using Microsoft.AspNetCore.Identity
@using TodoListApp.Components.Shared
@using TodoListApp.Data
@using TodoListApp.Models
@using TodoListApp.Services
@inject AuthenticationStateProvider _authenticationStateProvider
@inject UserManager<ApplicationUser> _userManager
@inject TodoListService _todoService

<PageTitle>TodoList</PageTitle>

<h1>Todo List</h1>

@if(IsAuthenticated){
    <p>@_userName (Authenticated)</p>
    <ul>
        @foreach (var todoItem in _todoItems)
        {
            <li>
                <span>Id: @todoItem.Id, @todoItem.Title</span> 
                @if (_editingTodoItem != null && _editingTodoItem.Id == todoItem.Id)
                {
                    <TodoItemEditor TodoItem="_editingTodoItem" OnSubmit="UpdateTodoAsync" Placeholder="Edit title" ButtonText="Save" />
                }
                else
                {
                    <button @onclick="() => EnterEditMode(todoItem)">Edit</button>
                }
                 
                <button @onclick="() => DeleteTodoAsync(todoItem.Id)">Delete</button>
            </li>
        }
    </ul>

    <TodoItemEditor TodoItem="_newTodoItem" OnSubmit="AddTodoAsync" Placeholder="New todo title" ButtonText="Add" />
}
else
{
    <p>Not authenticated</p>
}

@code {
    private List<TodoItem> _todoItems = new();
    private TodoItem? _newTodoItem;
    private TodoItem? _editingTodoItem;
    private string _userId = string.Empty;
    private string _userName = string.Empty;

    private bool IsAuthenticated => !string.IsNullOrEmpty(_userId);

    protected override async Task OnInitializedAsync()
    {
        var authState = await _authenticationStateProvider.GetAuthenticationStateAsync();
        var user = authState.User;

        if (user.Identity?.IsAuthenticated == true)
        {
            _userId = _userManager.GetUserId(user) ?? string.Empty;
            _userName = user.Identity.Name ?? string.Empty;
            if (IsAuthenticated)
            {
                CreateNewTodo();
                await ReloadTodosAsync();
            }
        }
    }

    private void CreateNewTodo()
    {
        _newTodoItem = new TodoItem { UserId = _userId };
    }

    private async Task ReloadTodosAsync()
    {
        _todoItems = await _todoService.GetTodosAsync(_userId);

    }

    private void EnterEditMode(TodoItem todoItem)
    {
        _editingTodoItem = new TodoItem
            {
                Id = todoItem.Id,
                Title = todoItem.Title,
                UserId = todoItem.UserId
            };
    }

    private async Task UpdateTodoAsync()
    {
        if (_editingTodoItem != null)
        {
            await _todoService.UpdateTodoAsync(_userId, _editingTodoItem);
            _editingTodoItem = null;
            await ReloadTodosAsync();
        }
    }

    private async Task DeleteTodoAsync(int todoId)
    {
        await _todoService.DeleteTodoAsync(_userId, todoId);
        await ReloadTodosAsync();
    }

    private async Task AddTodoAsync()
    {
        if(_newTodoItem != null)
        {
            await _todoService.AddTodoAsync(_userId, _newTodoItem);
            CreateNewTodo();
            await ReloadTodosAsync();
        }
    }
}

…
<h1>Todo List</h1>

@* ログインしているユーザのTodo一覧を表示 *@
@if(IsAuthenticated){
    <p>@_userName (Authenticated)</p>
    <ul>
        @foreach (var todoItem in _todoItems)
        …
}
@* ログインしていなければNot authenticatedと表示 *@
else
{
    <p>Not authenticated</p>
}

@code {
    …
    private string _userId = string.Empty;
    private string _userName = string.Empty;

    private bool IsAuthenticated => !string.IsNullOrEmpty(_userId);

    protected override async Task OnInitializedAsync()
    {
        //ログインしていれば、ユーザ情報を取得して_userId、_userNameへ設定
        …
    }
…
//DBへのCRUD操作に対応するメソッド呼び出し(_userIdを使う)など
…