Hi,


using NHibernate with C#.

Stupid, I still can't figure out the use of "lazy".

Just take my class, Document, as example.
An Document instance can be parent of many Document instances; similarly, it can children of many parents. In short, it is self-referencing.
Document class has id field called docId.
It uses ISet to define the parentDocs, childDocs collections.

To support the many-to-many structure, I've used a table named DocInDocuments to store the parent-child relationship.

Problem:

How do I retrieve the child (parent) document instances of a given document in code? I have difficulty writing the HQL (IQuery) statement to fetch appropriately. Anybody can guide me the proper syntax? Let say, I want to retrieve all childDocs of a Document instance where its docId is 1?


Pls find below my Document.hbm.xml on childDocs and parentDocs set:

<set name="childDocs"
inverse="true"
lazy="true"
cascade="all-delete-orphan" table="DocInDocuments">
<key column="parentDoc" foreign-key="fkChildDocs" />
<many-to-many class="Business.Document, Business" outer-join="auto">
<column name="childDoc"/>
</many-to-many>
</set>
<set name="parentDocs"
inverse="false"
cascade="all-delete-orphan" table="DocInDocuments">
<key column="childDoc" foreign-key="fkParentDocs" />
<many-to-many class="Business.Document, Business" outer-join="auto">
<column name="parentDoc"/>
</many-to-many>
</set>


thanks in advance!
jackLing

I'm not very versed with HQL, but what about:



..something like that.

EDIT: re-reading your post made me think of this:



and lazy doesn't really matter here. Your collection will by hydrated if necessary (you can specify "inner join fetch", for example)

Hi,


Thanks for the reply!
But I still in misery....

If I were to use:
" from Document parent inner join fetch parent.childDocs children where parent.docId = 2"

it seems that the returned object is from the parent. But in fact, I want to retrieve all children documents (not the parent's info)


If I use HQL with "select chidren" in front (i.e. "select children from Document parent inner join fetch parent.childDocs children where parent.docId = 2";), I have problem getting the object array result (note: system prompts that need to use object array, Object[] in the following code). But then I find that the object array has zero length (i.e. objs[0] is invalid array index)...

Hope someone can give insights...! Thanks in advance!


sQuery = "select children from Document parent inner join fetch parent.childDocs children where parent.docId = 2";
IQuery q = sess.CreateQuery(sQuery);


for (IEnumerator ie = q.List().GetEnumerator(); ie.MoveNext(); )
{
Object[] objs = (Object[])ie.Current;
doc = (Document)objs[0];
System.Windows.Forms.MessageBox.Show(doc.name);

alResult.Add(doc);
}

i was reading in HIA today that if you structure your query WITHOUT the fetch, the query will actually return a 2-element array, the 0th index being your first Entity in the HQL query, and the 1st index being the 2nd....

(I may be mistaking this for the left join queries... where the first element might not have any of the 2nd element... thus a zero length array.... anyway if you have HIA it will really help here. )