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