Improve data seeding for the single-layer startup template.

Resolve #11384

```cs
dotnet run --migrate-database
dotnet .\MyCompanyName.MyProjectName.dll --migrate-database
```

templates/app-nolayers/MyCompanyName.MyProjectName/Data/DataSeederMiddleware.cs

@@ -1,48 +0,0 @@
-using Volo.Abp.Data;
-using Volo.Abp.DependencyInjection;
-using Volo.Abp.Identity;
-
-namespace MyCompanyName.MyProjectName.Data;
-
-public class DataSeederMiddleware : IMiddleware, ISingletonDependency
-{
-    private bool _hostSeeded;
-
-    private readonly ILogger<DataSeederMiddleware> _logger;
-    private readonly IDataSeeder _dataSeeder;
-
-    public DataSeederMiddleware(
-        ILogger<DataSeederMiddleware> logger,
-        IDataSeeder dataSeeder)
-    {
-        _logger = logger;
-        _dataSeeder = dataSeeder;
-    }
-
-    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
-    {
-        /* This logic is not safe if you are running multiple instances of your
-         * application in parallel. In that case, a distributed lock usage is suggested,
-         * or you can create another application for database migration/seed.
-         */
-        if (!_hostSeeded)
-        {
-            await SeedHostDataAsync();
-            _hostSeeded = true;
-        }
-
-        await next(context);
-    }
-
-    private Task SeedHostDataAsync()
-    {
-        _logger.LogInformation($"Executing database seed...");
-
-        return _dataSeeder.SeedAsync(new DataSeedContext()
-            .WithProperty(IdentityDataSeedContributor.AdminEmailPropertyName,
-                IdentityDataSeedContributor.AdminEmailDefaultValue)
-            .WithProperty(IdentityDataSeedContributor.AdminPasswordPropertyName,
-                IdentityDataSeedContributor.AdminPasswordDefaultValue)
-        );
-    }
-}

templates/app-nolayers/MyCompanyName.MyProjectName/Data/MyProjectNameDbMigrationService.cs

@@ -0,0 +1,88 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using Volo.Abp.Data;
+using Volo.Abp.DependencyInjection;
+using Volo.Abp.Identity;
+using Volo.Abp.MultiTenancy;
+using Volo.Abp.TenantManagement;
+
+namespace MyCompanyName.MyProjectName.Data;
+
+public class MyProjectNameDbMigrationService : ITransientDependency
+{
+    public ILogger<MyProjectNameDbMigrationService> Logger { get; set; }
+
+    private readonly IDataSeeder _dataSeeder;
+    private readonly MyProjectNameEFCoreDbSchemaMigrator _dbSchemaMigrator;
+    private readonly ITenantRepository _tenantRepository;
+    private readonly ICurrentTenant _currentTenant;
+
+    public MyProjectNameDbMigrationService(
+        IDataSeeder dataSeeder,
+        MyProjectNameEFCoreDbSchemaMigrator dbSchemaMigrator,
+        ITenantRepository tenantRepository,
+        ICurrentTenant currentTenant)
+    {
+        _dataSeeder = dataSeeder;
+        _dbSchemaMigrator = dbSchemaMigrator;
+        _tenantRepository = tenantRepository;
+        _currentTenant = currentTenant;
+
+        Logger = NullLogger<MyProjectNameDbMigrationService>.Instance;
+    }
+
+    public async Task MigrateAsync()
+    {
+        Logger.LogInformation("Started database migrations...");
+
+        await MigrateDatabaseSchemaAsync();
+        await SeedDataAsync();
+
+        Logger.LogInformation($"Successfully completed host database migrations.");
+
+        var tenants = await _tenantRepository.GetListAsync(includeDetails: true);
+
+        var migratedDatabaseSchemas = new HashSet<string>();
+        foreach (var tenant in tenants)
+        {
+            using (_currentTenant.Change(tenant.Id))
+            {
+                if (tenant.ConnectionStrings.Any())
+                {
+                    var tenantConnectionStrings = tenant.ConnectionStrings
+                        .Select(x => x.Value)
+                        .ToList();
+
+                    if (!migratedDatabaseSchemas.IsSupersetOf(tenantConnectionStrings))
+                    {
+                        await MigrateDatabaseSchemaAsync(tenant);
+
+                        migratedDatabaseSchemas.AddIfNotContains(tenantConnectionStrings);
+                    }
+                }
+
+                await SeedDataAsync(tenant);
+            }
+
+            Logger.LogInformation($"Successfully completed {tenant.Name} tenant database migrations.");
+        }
+
+        Logger.LogInformation("Successfully completed all database migrations.");
+        Logger.LogInformation("You can safely end this process...");
+    }
+
+    private async Task MigrateDatabaseSchemaAsync(Tenant tenant = null)
+    {
+        Logger.LogInformation($"Migrating schema for {(tenant == null ? "host" : tenant.Name + " tenant")} database...");
+        await _dbSchemaMigrator.MigrateAsync();
+    }
+
+    private async Task SeedDataAsync(Tenant tenant = null)
+    {
+        Logger.LogInformation($"Executing {(tenant == null ? "host" : tenant.Name + " tenant")} database seed...");
+
+        await _dataSeeder.SeedAsync(new DataSeedContext(tenant?.Id)
+            .WithProperty(IdentityDataSeedContributor.AdminEmailPropertyName, IdentityDataSeedContributor.AdminEmailDefaultValue)
+            .WithProperty(IdentityDataSeedContributor.AdminPasswordPropertyName, IdentityDataSeedContributor.AdminPasswordDefaultValue)
+        );
+    }
+}

templates/app-nolayers/MyCompanyName.MyProjectName/Data/MyProjectNameEFCoreDbSchemaMigrator.cs

@@ -0,0 +1,29 @@
+using Microsoft.EntityFrameworkCore;
+using Volo.Abp.DependencyInjection;
+
+namespace MyCompanyName.MyProjectName.Data;
+
+public class MyProjectNameEFCoreDbSchemaMigrator : ITransientDependency
+{
+    private readonly IServiceProvider _serviceProvider;
+
+    public MyProjectNameEFCoreDbSchemaMigrator(
+        IServiceProvider serviceProvider)
+    {
+        _serviceProvider = serviceProvider;
+    }
+
+    public async Task MigrateAsync()
+    {
+        /* We intentionally resolving the MyProjectNameDbContext
+         * from IServiceProvider (instead of directly injecting it)
+         * to properly get the connection string of the current tenant in the
+         * current scope.
+         */
+
+        await _serviceProvider
+            .GetRequiredService<MyProjectNameDbContext>()
+            .Database
+            .MigrateAsync();
+    }
+}

templates/app-nolayers/MyCompanyName.MyProjectName/MyCompanyName.MyProjectName.csproj

@@ -102,8 +102,4 @@
     </None>
   </ItemGroup>
 
-  <ItemGroup>
-    <Folder Include="Entities" />
-    <Folder Include="Services\Dtos" />
-  </ItemGroup>
 </Project>

templates/app-nolayers/MyCompanyName.MyProjectName/MyProjectNameModule.cs

@@ -286,7 +286,6 @@ public class MyProjectNameModule : AbpModule
             app.UseErrorPage();
         }
 
-        app.UseMiddleware<DataSeederMiddleware>();
         app.UseCorrelationId();
         app.UseStaticFiles();
         app.UseRouting();

templates/app-nolayers/MyCompanyName.MyProjectName/Program.cs

@@ -1,26 +1,35 @@
+using MyCompanyName.MyProjectName.Data;
 using Serilog;
 using Serilog.Events;
 
+
 namespace MyCompanyName.MyProjectName;
 
 public class Program
 {
     public async static Task<int> Main(string[] args)
     {
-        Log.Logger = new LoggerConfiguration()
+        var loggerConfiguration = new LoggerConfiguration()
 #if DEBUG
-        .MinimumLevel.Debug()
+            .MinimumLevel.Debug()
 #else
-        .MinimumLevel.Information()
+            .MinimumLevel.Information()
 #endif
-        .MinimumLevel.Override("Microsoft", LogEventLevel.Information)
+            .MinimumLevel.Override("Microsoft", LogEventLevel.Information)
-        .MinimumLevel.Override("Microsoft.EntityFrameworkCore", LogEventLevel.Warning)
+            .MinimumLevel.Override("Microsoft.EntityFrameworkCore", LogEventLevel.Warning)
-        .Enrich.FromLogContext()
+            .Enrich.FromLogContext()
-        .WriteTo.Async(c => c.File("Logs/logs.txt"))
+            .WriteTo.Async(c => c.File("Logs/logs.txt"))
 #if DEBUG
-        .WriteTo.Async(c => c.Console())
+            .WriteTo.Async(c => c.Console());
 #endif
-        .CreateLogger();
+        if (IsMigrateDatabase(args))
+        {
+            loggerConfiguration.MinimumLevel.Override("Volo.Abp", LogEventLevel.Warning);
+            loggerConfiguration.MinimumLevel.Override("Microsoft", LogEventLevel.Warning);
+            loggerConfiguration.MinimumLevel.Override("IdentityServer4.Startup", LogEventLevel.Warning);
+        }
+
+        Log.Logger = loggerConfiguration.CreateLogger();
 
         try
         {
@@ -32,6 +41,12 @@ public class Program
             var app = builder.Build();
             await app.InitializeApplicationAsync();
 
+            if (IsMigrateDatabase(args))
+            {
+                await app.Services.GetRequiredService<MyProjectNameDbMigrationService>().MigrateAsync();
+                return 0;
+            }
+
             Log.Information("Starting MyCompanyName.MyProjectName.");
             await app.RunAsync();
             return 0;
@@ -51,4 +66,9 @@ public class Program
             Log.CloseAndFlush();
         }
     }
+
+    private static bool IsMigrateDatabase(string[] args)
+    {
+        return args.Any(x => x.Contains("--migrate-database", StringComparison.OrdinalIgnoreCase));
+    }
 }