Hi i am new to hibernate

I have three tables.
Table1
Project
ID


POJO
Project
Set<Milestone>
id(int)


Table2
MilestoneType
code

POJO
MilestoneType
set<Milestone>
code(int)

Table 3
Milestone
ID(from Project)
code(from MilestoneType)
desc

POJO
Milestone
object of Project
object of MilestoneType
description(String)

Table1 has one-to-many relation with Table3
Table2 also has one -to-many relation with Table3

i need to write a criteria from Project to check the desc of Milestone table.
I tried createAlias("Milestone","Milestone").createAlias("Milestone.MilestoneType","MilestoneAlias");

then i added the restriction
criteria.add(Restrictions.eq("MilestoneAlias.desc","description"));

but it showed me SQL grammar exception saying "MilestoneAlias12_.desc" invalid identifier

can anyone resolve this..