Linq - 关于子 object 的 where 子句

Question

Given the following classes:

public class Nation
{
  public string Name { get; set; }
  public IEnumerable<City> Cities { get; private set; }
}

public class City
{
  public string Name { get; set; }
}

Assume Nation is the aggregate root and so I only have a NationRepository and not a CityRepository (thus Nation is the starting point for Linq queries). To clarify, my starting point would be an IQueryable<Nation> object.

How would I write a query which returns a collection of City objects according to the following logic:

Select all City instances whose Name begins with 'M' whose parent Nation 's name is 'UK'?

Answer 1

You would do the following:

var results = NationRepository.Where(n => n.Name == "UK")
                              .SelectMany(n => n.Cities)
                              .Where(c => c.Name.StartsWith("M"));

Answer 2

Like this:

from n in Nation
where n.Name == "UK"
from c in n.Cities
where c.Name.StartsWith("M")
select c

Answer 3

var result = nations.Where(n => n.Name == "UK")
                    .SelectMany(n => n.Cities)
                    .Where(c => c.Name.StartsWith("M"));

EDIT: Since @Justin Niessner beat me... maybe nest the second where clause

var result = nations.Where(n => n.Name == "UK")
                    .SelectMany(n => n.Cities.Where(c => c.Name.StartsWith("M"));