Index with two collections - ravendb

Question

I am struggling creating an simple index with ravendb.
Given are two document collections:
User (34000 docs) and
BlogEntries (1.5 million docs)
1) How can I create an index that shows the count of blog entries for each user?
The collections relationship is as following:
User.LastName + "," + User.FirstName = Blog.CreatedBy
Important is the fact that BlogEntries contains old entries that are not related to the user collection. I want to filter those entries out, so that they are not appear in the index. That's why I need the user collection here.
Sample Data:
User Collection:
User U1
User U2
BlogEntry Collection:
BlogEntry B1 -> U1
BlogEntry B2 -> U1
BlogEntry B3 -> U2
BlogEntry B4 -> XYZ1
BlogEntry B5 -> XYZ2
BlogEntry B6 -> U1
I want to filter out the B4 and B5 entries, cause they are not related to a user in the user collection.
2) Do I have to use a multimap index for that?
3) I already tried the following via the management studio, but the index does not work.
Seems I cannot use two document collections in a single map block.
Map:
from user in docs.Users
from blog in docs.Blogs
where blog.CreatedBy = user.LastName + "," + user.FirstName
select new { UserName = user.LastName ..., Count = 1 }
Reduce:
from result in results group by result.UserName
into g
select new { User = g.Key, g.Sum( x => x.Count) }
Thanks,
Marius

Answer 1

With the changed requirement I guess you need a multi map index:
AddMap<User>(users => from user in users
select new
{
UserName = user.LastName + "," + user.FirstName,
HasUser = true,
Count = 0
});
AddMap<BlogEntry>(blogEntries => from blogEntry in blogEntries
select new
{
UserName = blogEntry.CreatedBy,
HasUser = false,
Count = 1
});
Reduce = results => from result in results
group result by result.UserName
into g
select new
{
UserName = g.Key,
HasUser = g.Any(x => x.HasUser),
Count = g.Sum(x => x.Count)
};
You can filter the index by the HasUser property.