DevOps/5/Program.cs

using Example.Data;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;

var builder = WebApplication.CreateBuilder(args);

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection")
    ?? throw new InvalidOperationException("Connection string 'DefaultConnection' was not found.");
var configuredProvider = builder.Configuration["Database:Provider"]
    ?? throw new InvalidOperationException("Database provider configuration 'Database:Provider' was not found.");

if (builder.Environment.IsDevelopment())
{
    EnsureProviderMatchesEnvironment(configuredProvider, expectedProvider: "Sqlite", builder.Environment.EnvironmentName);
    ValidateConnectionString(connectionString, configuredProvider);

    builder.Services.AddDbContext<ApplicationDbContext, SqliteApplicationDbContext>(options =>
        options.UseSqlite(connectionString));
}
else
{
    EnsureProviderMatchesEnvironment(configuredProvider, expectedProvider: "Postgres", builder.Environment.EnvironmentName);
    ValidateConnectionString(connectionString, configuredProvider);

    builder.Services.AddDbContext<ApplicationDbContext, PostgresApplicationDbContext>(options =>
        options.UseNpgsql(connectionString));
}

builder.Services.AddDatabaseDeveloperPageExceptionFilter();

var identityBuilder = builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true);
if (builder.Environment.IsDevelopment())
{
    identityBuilder.AddEntityFrameworkStores<SqliteApplicationDbContext>();
}
else
{
    identityBuilder.AddEntityFrameworkStores<PostgresApplicationDbContext>();
}

builder.Services.AddControllersWithViews();

var app = builder.Build();

using (var services = app.Services.CreateScope())
{
    var db = services.ServiceProvider.GetRequiredService<ApplicationDbContext>();
    db.Database.Migrate();

    if (app.Environment.IsDevelopment())
    {
        ApplicationDbInitializer.SeedDevelopmentData(db);
    }
}

if (app.Environment.IsDevelopment())
{
    app.UseMigrationsEndPoint();
}
else
{
    app.UseExceptionHandler("/Home/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthentication();
app.UseAuthorization();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");
app.MapRazorPages();

app.Run();

static void EnsureProviderMatchesEnvironment(string configuredProvider, string expectedProvider, string environmentName)
{
    if (!string.Equals(configuredProvider, expectedProvider, StringComparison.OrdinalIgnoreCase))
    {
        throw new InvalidOperationException(
            $"Environment '{environmentName}' must use the '{expectedProvider}' database provider, but configuration specifies '{configuredProvider}'.");
    }
}

static void ValidateConnectionString(string connectionString, string configuredProvider)
{
    if (string.Equals(configuredProvider, "Sqlite", StringComparison.OrdinalIgnoreCase))
    {
        if ((!connectionString.Contains("Data Source=", StringComparison.OrdinalIgnoreCase) &&
             !connectionString.Contains("DataSource=", StringComparison.OrdinalIgnoreCase)) ||
            connectionString.Contains("Host=", StringComparison.OrdinalIgnoreCase) ||
            connectionString.Contains("Server=", StringComparison.OrdinalIgnoreCase))
        {
            throw new InvalidOperationException("The development connection string does not look like a valid SQLite connection string.");
        }

        return;
    }

    if (string.Equals(configuredProvider, "Postgres", StringComparison.OrdinalIgnoreCase))
    {
        if (!connectionString.Contains("Host=", StringComparison.OrdinalIgnoreCase) ||
            connectionString.Contains("Server=", StringComparison.OrdinalIgnoreCase) ||
            connectionString.Contains("DataSource=", StringComparison.OrdinalIgnoreCase))
        {
            throw new InvalidOperationException("The production connection string does not look like a valid PostgreSQL connection string.");
        }

        return;
    }

    throw new InvalidOperationException($"Unsupported database provider '{configuredProvider}'.");
}