var vids = from v in versions
		    join a in DbContext.AttributeValues on v.ID equals a.ObjectVersionID
                          join x in attrs on a.AttributeID equals x.id
                          where a.Value == x.value
                          select v;

int res = vids.Count();

Dictionary<string, MyInfo>

var attrs = from d in attributes.AsQueryable()
		                select new {id = d.Value.AttributeID, value = d.Value.Value};

var vids = from v in versions
		    join a in DbContext.AttributeValues on v.ID equals a.ObjectVersionID
                          join x in attrs on a.AttributeID equals x.id
                          where a.Value == x.value
                          select v;

int res = vids.Count();

Dictionary<string, MyInfo>