I have a question - sorry of it is too application specific:

I am implementing some meta-data kind of thing in my application. Say I have one domain object D which canbe defined by a number of attribute groups, which in turn consists of a number of attributes.

so D <one-to-many> attribute groups <one-to-many> attributes

an attribute group simply has (name) and
an attribute has (name, value)

So here is the mappings:

domain object
----------------
<class name="D" ...>
......
<set name="attributeGroups" lazy="true" cascade="all-delete-orphan">
<key column="D_ID"/>
<one-to-many class="AttributeGroup"/>
</set>

</class>

attribute group
----------------
<class name="AttributeGroup" ...>
......
<set name="attributes" cascade="all-delete-orphan" lazy="true">
<key column="ATTRIBUTEGROUP_ID"/>
<one-to-many class="Attribute"/>
</set>

</class>

attribute
----------
<class name="Attribute" ...>
......
<property name="name" type="string" not-null="true" column="NAME"/>
<property name="value" type="string" not-null="false" column="VALUE"/>

</class>


So now I want to get a list of objects D with certain creteria. for example, when attribute.name=".." and attribute.value="...".

How can I use join to do this?

I can do this:
<b>
select d from D d join d.attributeGroups ag where ag.name="ag1"
</b>
this will return a list of Ds if there is an attributeGroup called 'ag1'.

but how to go down to the next level (attribute level) ?

this gives me error:
<b>
select d from D d join d.attributeGroups.attributes a where a.name="..."
</b>
thanks
li xin chu

the error that I am getting by running the second sql statement is:

1 errors occurred while listing (and calling getPathNames).
net.sf.hibernate.QueryException: expecting 'elements' or 'indices' after: attributes [select org from Org as org join org.attributeGroups.attributes attribute]

I can query with one condition now:

select d from D as d join d.attributeGroups as attributeGroup join attributeGroup.attributes as attribute where attribute.name="a2" and attribute.value="a2"

but what do I need to do so that I can check multiple conditions ? For example, to get the Ds if two attributes exists, one with name a1, value v1 and another with name a2, and value v2 ?

seems that i need to work on the attributes table directly....

I can only think of using intersect (hence native sql) to handle multiple conditions like this.

any better idea ?