NHibernate eager loaded tree hits the database when walked by Automapper - nhibernate

Question

I ran into a strange NHibernate and Automapper problem. I am not sure which one is to blame but I am struggling for a whole day now and I can't seem to find out why.
Here is my Nhibernate mapping files:
Navigation.hbm.xml
<id name="ID" column="NavigationID">
<generator class="identity"></generator>
</id>
<property name="IsDefault"/>
<property name="RoleType" column="RoleTypeID" />
<bag name="Items" cascade="save-update" inverse="true" lazy="false" fetch="join">
<key column="NavigationID"/>
<one-to-many class="NavigationItem"/>
</bag>
NavigationItem.hbm.xml
<class name="NavigationItem" table="NavigationItem">
<id name="ID" column="NavigationItemID">
<generator class="identity"></generator>
</id>
<property name="ShowInMenu"/>
<property name="Order" column="[Order]" />
<many-to-one name="Page" column="PageID" lazy="false" fetch="join" />
<many-to-one name="Navigation" column="NavigationID" />
<many-to-one name="Parent" column="ParentNavigationItemID" />
<bag name="Items" cascade="save-update" inverse="true">
<key column="ParentNavigationItemID"/>
<one-to-many class="NavigationItem"/>
</bag>
This is how I fill up a Navigation object:
ISession session = SessionProvider.Instance.CurrentSession;
using (transaction = session.BeginTransaction())
{
var navigation = session.QueryOver<Navigation>()
.Where(x => x.IsDefault && x.RoleType == null)
.TransformUsing(new NHibernate.Transform.RootEntityResultTransformer())
.SingleOrDefault();
transaction.Commit();
return navigation;
}
Since the Items bag on the Navigation object is set to lazy="false", I get only one query to the database to get the Navigation object and a left join to get all the Navigation items as well.
All is perfect until now.
I did a test to iterate through all the items and the sub-items recursive and no more hits to the database.
Then, I have an UI model that I map with Automapper.
Here are the UI models:
public class NavigationModel
{
public List<NavigationItemModel> Items { get; set; }
public NavigationModel()
{
Items = new List<NavigationItemModel>();
}
}
public class NavigationItemModel
{
public string PageName { get; set; }
public string Url { get; set; }
public bool Selected { get; set; }
public NavigationItemModel Parent { get; set; }
public List<NavigationItemModel> Items { get; set; }
}
And the automapper mappings:
AutoMapper.Mapper
.CreateMap<NavigationItem, NavigationItemModel>()
// IF I REMOVE THE NEXT LINE, IT HITS THE DATABASE FOR EACH SUB-ITEM of the NavigationItem.Items
.ForMember(m => m.Items, o => o.Ignore());
AutoMapper.Mapper
.CreateMap<Navigation, NavigationModel>();
Ok, now the behavior is like this:
If I ignore the NavigationItem.Items member in the mapping, all goes well, but only the Navigation and it's items are mapped. No sub-items collection of the navigation's Items are mapped. BUT the database is not hit anymore. But I want the other items mapped as well...
If I remove the line under the comment, the database is hit for each of the Navigation.Items, querying for it's sub-items (where ParentID = Item.ID).
Any idea what am I doing wrong?
Sorry for the wall of text, but I thought better to describe it in more detail, I spent the whole day on this one and I tried all kind of queries with Future and JoinQueryOver, etc. The problem does not seem to be with NHibernate since that loads fine and I can iterate without any more calls to the database.
I forgot to include the SQL that is being generated:
First there is this query:
SELECT this_.NavigationID as Navigati1_7_2_,
this_.IsDefault as IsDefault7_2_,
this_.RoleTypeID as RoleTypeID7_2_,
items2_.NavigationID as Navigati5_4_,
items2_.NavigationItemID as Navigati1_4_,
items2_.NavigationItemID as Navigati1_4_0_,
items2_.ShowInMenu as ShowInMenu4_0_,
items2_.[Order] as column3_4_0_,
items2_.PageID as PageID4_0_,
items2_.NavigationID as Navigati5_4_0_,
items2_.ParentNavigationItemID as ParentNa6_4_0_,
page3_.PageID as PageID8_1_,
page3_.Name as Name8_1_,
page3_.Title as Title8_1_,
page3_.Description as Descript4_8_1_,
page3_.URL as URL8_1_
FROM Navigation this_
left outer join NavigationItem items2_
on this_.NavigationID = items2_.NavigationID
left outer join Page page3_
on items2_.PageID = page3_.PageID
WHERE (this_.IsDefault = 1 /* #p0 */
and this_.RoleTypeID is null)
Then, when Automapper comes into play, a list of these queries are being generated, only the p0 parameter differs (from 1 to 12 ... the number of items without parents )
SELECT items0_.ParentNavigationItemID as ParentNa6_2_,
items0_.NavigationItemID as Navigati1_2_,
items0_.NavigationItemID as Navigati1_4_1_,
items0_.ShowInMenu as ShowInMenu4_1_,
items0_.[Order] as column3_4_1_,
items0_.PageID as PageID4_1_,
items0_.NavigationID as Navigati5_4_1_,
items0_.ParentNavigationItemID as ParentNa6_4_1_,
page1_.PageID as PageID8_0_,
page1_.Name as Name8_0_,
page1_.Title as Title8_0_,
page1_.Description as Descript4_8_0_,
page1_.URL as URL8_0_
FROM NavigationItem items0_
left outer join Page page1_
on items0_.PageID = page1_.PageID
WHERE items0_.ParentNavigationItemID = 1 /* #p0 */
This is taken from the NHProf application, hope it helps.
Thank you,
Cosmin

Answer 1

I think AutoMapper is mapping your classes recursively. If this is the case, than you can specifiy the max depth for your mappings using
Mapper.CreateMap<TSource, TDestination>().MaxDepth(2); // or 1, or 3, or whatever