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<p style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; -webkit-line-clamp: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;" data-pasted="true">ログイン後に自動的にユーザー専用のデータベースを作成する仕組み。 これはマルチテナント（ユーザーごとにDBを分ける）に近い構成で、Identity の認証後に EF Core を使って動的に DB を生成する流れになります。<p style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; -webkit-line-clamp: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">以下は実装の考え方とサンプルコードです。<p style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; -webkit-line-clamp: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">1. 基本の流れ<ol style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">ユーザーがログイン成功</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">ログインしたユーザーの <code style="border: 1px solid rgb(221, 221, 221); border-radius: 4px; padding: 1px 4px; background: rgb(255, 255, 255); font: 14px / 20px monospace;">Id</code> または <code style="border: 1px solid rgb(221, 221, 221); border-radius: 4px; padding: 1px 4px; background: rgb(255, 255, 255); font: 14px / 20px monospace;">UserName</code> を取得</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">そのユーザー専用の接続文字列を生成</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">EF Core の <code style="border: 1px solid rgb(221, 221, 221); border-radius: 4px; padding: 1px 4px; background: rgb(255, 255, 255); font: 14px / 20px monospace;">DbContext</code> を使って <code style="border: 1px solid rgb(221, 221, 221); border-radius: 4px; padding: 1px 4px; background: rgb(255, 255, 255); font: 14px / 20px monospace;">Database.EnsureCreated()</code> または <code style="border: 1px solid rgb(221, 221, 221); border-radius: 4px; padding: 1px 4px; background: rgb(255, 255, 255); font: 14px / 20px monospace;">Migrate()</code> を実行</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">必要なら初期データ投入</li></ol><p style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; -webkit-line-clamp: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">2. サンプル実装（概念コード）<pre data-priority="2" style="color: rgb(17, 17, 17); font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><code style="border: 1px solid rgb(221, 221, 221); border-radius: 8px; padding: 12px 20px; background: rgb(255, 255, 255); font: 14px / 20px monospace; display: block; white-space: pre-wrap; margin-right: 20px;">public class UserSpecificDbContext : DbContext
{
 private readonly string _connectionString;

 public UserSpecificDbContext(string connectionString)
 {
 _connectionString = connectionString;
 }

 protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
 {
 optionsBuilder.UseSqlServer(_connectionString);
 }

 public DbSet&lt;UserData&gt; UserData { get; set; }
}

public class UserDatabaseService
{
 private readonly UserManager&lt;IdentityUser&gt; _userManager;
 private readonly IConfiguration _config;

 public UserDatabaseService(UserManager&lt;IdentityUser&gt; userManager, IConfiguration config)
 {
 _userManager = userManager;
 _config = config;
 }

 public async Task CreateUserDatabaseAsync(IdentityUser user)
 {
 var baseConn = _config.GetConnectionString(&quot;BaseTemplate&quot;);
 var userDbName = $&quot;UserDB_{user.Id}&quot;;
 var connStr = baseConn.Replace(&quot;{DB_NAME}&quot;, userDbName);

 using var db = new UserSpecificDbContext(connStr);
 await db.Database.EnsureCreatedAsync();
 }
}
</code></pre><p style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; -webkit-line-clamp: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">3. ログイン後に呼び出す例<pre data-priority="2" style="color: rgb(17, 17, 17); font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><code style="border: 1px solid rgb(221, 221, 221); border-radius: 8px; padding: 12px 20px; background: rgb(255, 255, 255); font: 14px / 20px monospace; display: block; white-space: pre-wrap; margin-right: 20px;">public class AccountController : Controller
{
 private readonly SignInManager&lt;IdentityUser&gt; _signInManager;
 private readonly UserManager&lt;IdentityUser&gt; _userManager;
 private readonly UserDatabaseService _dbService;

 public AccountController(
 SignInManager&lt;IdentityUser&gt; signInManager,
 UserManager&lt;IdentityUser&gt; userManager,
 UserDatabaseService dbService)
 {
 _signInManager = signInManager;
 _userManager = userManager;
 _dbService = dbService;
 }

 [HttpPost]
 public async Task&lt;IActionResult&gt; Login(LoginViewModel model)
 {
 var result = await _signInManager.PasswordSignInAsync(model.Email, model.Password, false, false);
 if (result.Succeeded)
 {
 var user = await _userManager.FindByEmailAsync(model.Email);
 await _dbService.CreateUserDatabaseAsync(user);
 return RedirectToAction(&quot;Index&quot;, &quot;Home&quot;);
 }
 return View(model);
 }
}
</code></pre><p style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; -webkit-line-clamp: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">4. 注意点<ul style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">DB数が増えると管理コストが高くなる（バックアップ・マイグレーション・接続プールなど）</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">実運用では「ユーザーごとにスキーマを分ける」か「テーブルでユーザーIDをキーにする」方が一般的</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">Azure SQL や PostgreSQL などでは動的DB作成に権限設定が必要</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">マイグレーションを適用する場合は <code style="border: 1px solid rgb(221, 221, 221); border-radius: 4px; padding: 1px 4px; background: rgb(255, 255, 255); font: 14px / 20px monospace;">Migrate()</code> を使うと便利</li></ul><p style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; -webkit-line-clamp: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">もし希望があれば、この仕組みを&nbsp;「ユーザーごとに別スキーマを作る」方式 に書き換えたコード例も作れます。 そちらの方がスケーラブルで運用しやすいですよ。<p style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; -webkit-line-clamp: revert; color: rgb(17, 17, 17); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(249, 249, 249); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">作りますか？Powered by <a href="https://www.froala.com/wysiwyg-editor?pb=1" title="Froala Editor">Froala Editor</a>

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