Linq - Joining through a dictionary where the KeyValuePair.Value is a collection itself

trying to get my head round what the joins should look like for the example below. Any help determining if it is poss开发者_开发技巧ible to write linq for the following would be greatly apprieciated!

        List<string> col1;
        Dictionary<string, List<string>> join2;

I wish to select all keys from the dictionary where the items in col1 exist in the Value List collection of the dictionary.

        IEnumerable<string> query = from c1 in col1
                                    join kvp in join2 on c1 equals kvp.Value
                                    where c1 == "foo"
                                    orderby kvp.Key
                                    select kvp.Key;

Obviously the above fails as kvp.Value is a List and not a string to equate to c1 - any pointers?

I am not sure why the join is needed... if you are select on "foo" then the following would yield the same result:

        IEnumerable<string> query = from kvp in join2
                                where kvp.Value.Contains ("foo")
                                orderby kvp.Key
                                select kvp.Key;

Alternatively with the join

        IEnumerable<string> query = from c1 in col1 where c1 == "foo" from kvp in join2 
                                where kvp.Value.Contains (c1) 
                                orderby kvp.Key
                                select kvp.Key;

from kvp in dict
from e in kvp.Value
... // join on e here

var result = from c1 in col1.Keys
             from c2 in col1.Values
             where c1 == c2
             select c1;