Miguel,

In your database do you have relationships setup. When you create your LINQ
to SQL classes it uses the relationship data to determine the shape of the
objects. I created the 5 tables that you mentioned;

Post
File
Tag
PostTag
FileTag

I then setup the relationships inside if Enterprise manager. Created a LINQ
to SQL class including all of the tables. and then wrote the following
query;

LinqTestDbDataContext db = new LinqTestDbDataContext();

db.Log = Console.Out;

var values = from file in db.Files

select new { file.FileTag.Tag };

foreach (var value in values)

{

Console.WriteLine(value.Tag.TagID.ToString());

}

with the logging on I inspected the SQL that was created for execution

SELECT [t3].[test], [t3].[TagID], [t3].[TagDescription]

FROM [dbo].[File] AS [t0]

LEFT OUTER JOIN [dbo].[FileTag] AS [t1] ON [t1].[FileTagID] = [t0].[FileID]

LEFT OUTER JOIN (

SELECT 1 AS [test], [t2].[TagID], [t2].[TagDescription]

FROM [dbo].[Tag] AS [t2]

) AS [t3] ON [t3].[TagID] = [t1].[TagID]

As you can see it does work with Many-to-Many relationships. Just make sure
that you have relationships defined in the database.

Mark