Nhibernate multilevel hierarchy save error?

Question

Hi,

I have a database with a 6 level hierarchy and a domain model on top of that. something like this:

Category -SubCategory -Container -DataDescription | Meta data -Data

The mapping I'm using follows the following pattern:

  <class name="Category, Sample" table="Categories">
    <id name="Id" column="Id" type="System.Int32" unsaved-value="0">
      <generator class="native"/>
    </id>    
    <property name="Name" access="property" type="String" column="Name"/>
    <property name="Metadata" access="property" type="String" column="Metadata"/>
    <bag name="SubCategories" 
      cascade="save-update" 
      lazy="true" 
      inverse="true">
      <key column="Id" foreign-key="category_subCategory_fk"/>
      <one-to-many class="SubCategory, Sample" />
    </bag>
  </class>

<class name="SubCategory, Sample" table="SubCategories">
 <id name="Id" column="Id" type="System.Int32" unsaved-value="0">
  <generator class="native"/>
 </id>
 <many-to-one name="Category"
     class="Category, Sample"
     foreign-key="subCat_category_fk"/>

 <property name="Name" access="property" type="String"/>
 <property name="Metadata" access="property" type="String"/>

 <bag name="Containers"
   inverse="true"
   cascade="save-update"
   lazy="true">
  <key column="Id" foreign-key="subCat_container_fk" />
  <one-to-many class="Container, Sample" />
 </bag>
</class>

<class name="Container, Sample" table="Containers">
 <id name="Id" column="Id" type="System.Int32" unsaved-value="0">
  <generator class="assigned"/>
 </id>
 <many-to-one name="SubCategory"
     class="SubCategory,Sample"      
     foreign-key="container_subCat_fk"/> 

 <property name="Name" access="property" type="String" column="Name"/>

 <bag name="DataDescription" cascade="all" lazy="true" inverse="true">
  <key column="Id" foreign-key="container_ DataDescription_fk"/>
  <one-to-many class="DataDescription, Sample" />
 </bag>

 <bag name="MetaData" cascade="all" lazy="true" inverse="true">
  <key column="Id" foreign-key="container_metadata_cat_fk"/>
  <one-to-many class="MetaData, Sample" />
 </bag>
</class>

For some reason when I try to save the category (with the subcategory, container etc. attached) I get a foreign key violation from the database.

The code is something like this (Pseudo).

var category = new Category();
var subCategory = new SubCategory();
var container = new Container();
var dataDescription = new DataDescription();
var metaData = new MetaData();

category.AddSubCategory(subCategory);
subCategory.AddContainer(container);
container.AddDataDescription(dataDescription);
container.AddMetaData(metaData);

Session.Save(category);

Here is the log from this test :

DEBUG NHibernate.SQL - INSERT INTO Categories (Name, Metadata) VALUES (@p0, @p1); select SCOPE_IDENTITY(); @p0 = 'Unit test', @p1 = 'unit test'

DEBUG NHibernate.SQL - INSERT INTO SubCategories (Category, Name, Metadata) VALUES (@p0, @p1, @p2); select SCOPE_IDENTITY(); @p0 = '1', @p1 = 'Unit test', @p2 = 'unit test'

DEBUG NHibernate.SQL - INSERT INTO Containers (SubCategory, Name, Frequency, Scale, Measurement, Currency, Metadata, Id) VALUES (@p0, @p1, @p2, @p3, @p4, @p5, @p6, @p7); @p0 = '1', @p1 = 'Unit test', @p2 = '15', @p3 = '1', @p4 = '1', @p5 = '1', @p6 = 'unit test', @p7 = '0'

ERROR NHibernate.Util.ADOExceptionReporter - The INSERT statement conflicted with the FOREIGN KEY constraint "subCat_container_fk". The conflict occurred in database "Sample", table "dbo.SubCategories", column 'Id'.

The methods for adding items to objects is always as follows:

public void AddSubCategory(ISubCategory subCategory)
{
    subCategory.Category = this;
    SubCategories.Add(subCategory);
}

What am I missing??

Thanks, nisbus

Answer 1

Well I found the error.

I needed to name the columns in the mappings one-to-many and many-to-one something other than Id to make this work correctly.

The correct mapping would look something like this:

 <class name="Category, Sample" table="Categories">
    <id name="Id" column="Id" type="System.Int32" unsaved-value="0">
      <generator class="native"/>
    </id>    
    <property name="Name" access="property" type="String" column="Name"/>
    <property name="Metadata" access="property" type="String" column="Metadata"/>
    <bag name="SubCategories" 
         cascade="save-update" 
         lazy="true" 
         inverse="true">
      <key column="Category_Id" foreign-key="category_subCategory_fk"/>
      <one-to-many class="SubCategory, Sample" />
    </bag>
  </class>

<class name="SubCategory, Sample" table="SubCategories">
        <id name="Id" column="Id" type="System.Int32" unsaved-value="0">
                <generator class="native"/>
        </id>
        <many-to-one name="Category"
                                 class="Category, Sample"
                                 column="Category_Id"
                                 foreign-key="subCat_category_fk"/>

        <property name="Name" access="property" type="String"/>
        <property name="Metadata" access="property" type="String"/>

        <bag name="Containers"
                 inverse="true"
                 cascade="save-update"
                 lazy="true">
                <key column="Container_Id" foreign-key="subCat_container_fk" />
                <one-to-many class="Container, Sample" />
        </bag>
</class>

Everything works great now.

Thanks, nisbus