在列表中使用Where和列表

var cities = from country in countrList
             from city in country.Cities
             where city.Name.Contains("New")
             select city;

或:

var cities = countrList
    .SelectMany(country => country.Cities)
    .Where(city => city.Name.Contains("New"));

尝试 countriesList.FirstOrDefault( x => x.Cities.Any( y => y.Name.Contains("New"));

var cities = countryList.SelectMany(country => country.Cities)
                        .Where(city => city.Name.Contains("New"))
                        .ToList();

countrList.Where(x=>x.Cities.Any(y=>y.Name.Contains("New")));