RestaurantApp/Database.cs

using System;
using Npgsql;

namespace RestaurantApp.DAL
{
    public static class Database
    {
        private const string Host = "edu-pg.itiscaf.ru";
        private const int Port = 5432;
        private const string DbName = "dbwork";
        private const string User = "shagavaliev_iv";
        private const string Password = "75&n057$380";
        private const string Schema = "shagavaliev_iv";

        public static string ConnectionString =>
            $"Host={Host};Port={Port};Database={DbName};Username={User};Password={Password};Search Path={Schema};";

        public static NpgsqlConnection GetConnection()
        {
            var conn = new NpgsqlConnection(ConnectionString);
            conn.Open();
            return conn;
        }

        public static bool TestConnection(out string error)
        {
            error = "";
            try
            {
                using (var conn = GetConnection()) { }
                return true;
            }
            catch (Exception ex)
            {
                error = ex.Message;
                return false;
            }
        }
    }
}