food-market/src/food-market.api/Seed/SystemReferenceSeeder.cs

using foodmarket.Domain.Catalog;
using foodmarket.Infrastructure.Persistence;
using Microsoft.EntityFrameworkCore;

namespace foodmarket.Api.Seed;

// Seeds global reference data (countries, currencies). Runs in all environments.
public class SystemReferenceSeeder : IHostedService
{
    private readonly IServiceProvider _services;

    public SystemReferenceSeeder(IServiceProvider services)
    {
        _services = services;
    }

    public async Task StartAsync(CancellationToken ct)
    {
        using var scope = _services.CreateScope();
        var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();

        await SeedCountriesAsync(db, ct);
        await SeedCurrenciesAsync(db, ct);
        await db.SaveChangesAsync(ct);
    }

    public Task StopAsync(CancellationToken ct) => Task.CompletedTask;

    private static async Task SeedCountriesAsync(AppDbContext db, CancellationToken ct)
    {
        // Kazakhstan first, then common trade partners.
        var wanted = new[]
        {
            new Country { Code = "KZ", Name = "Казахстан", SortOrder = 1 },
            new Country { Code = "RU", Name = "Россия", SortOrder = 2 },
            new Country { Code = "CN", Name = "Китай", SortOrder = 3 },
            new Country { Code = "TR", Name = "Турция", SortOrder = 4 },
            new Country { Code = "BY", Name = "Беларусь", SortOrder = 5 },
            new Country { Code = "UZ", Name = "Узбекистан", SortOrder = 6 },
            new Country { Code = "KG", Name = "Кыргызстан", SortOrder = 7 },
            new Country { Code = "DE", Name = "Германия", SortOrder = 10 },
            new Country { Code = "US", Name = "США", SortOrder = 11 },
            new Country { Code = "KR", Name = "Южная Корея", SortOrder = 12 },
            new Country { Code = "IT", Name = "Италия", SortOrder = 13 },
            new Country { Code = "PL", Name = "Польша", SortOrder = 14 },
        };

        var existingCodes = await db.Countries.Select(c => c.Code).ToListAsync(ct);
        foreach (var c in wanted)
        {
            if (!existingCodes.Contains(c.Code))
            {
                db.Countries.Add(c);
            }
        }
    }

    private static async Task SeedCurrenciesAsync(AppDbContext db, CancellationToken ct)
    {
        var wanted = new[]
        {
            new Currency { Code = "KZT", Name = "Тенге", Symbol = "₸", MinorUnit = 2 },
            new Currency { Code = "RUB", Name = "Российский рубль", Symbol = "₽", MinorUnit = 2 },
            new Currency { Code = "USD", Name = "Доллар США", Symbol = "$", MinorUnit = 2 },
            new Currency { Code = "EUR", Name = "Евро", Symbol = "€", MinorUnit = 2 },
            new Currency { Code = "CNY", Name = "Китайский юань", Symbol = "¥", MinorUnit = 2 },
        };

        var existingCodes = await db.Currencies.Select(c => c.Code).ToListAsync(ct);
        foreach (var c in wanted)
        {
            if (!existingCodes.Contains(c.Code))
            {
                db.Currencies.Add(c);
            }
        }
    }
}