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POBidirectional one to many (or many to one) cascade delete behaviour. It works, but why?
 

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    <p>I have two Nhibernate mappings for two classes, Category and Product. My Category class has two properties that are collections. The Children property is a collection of type Category which represents child categories (represents a category menu, typical parent child scenario). The second property on the Category class is a Products collection which represents all the products under a category.</p> <p>What I am trying achieve is when I delete a category I want the category to deleted but not the product. So I want the product to be orphaned. i.e have its foreign key (CategoryId) in the Product table set to null. I don't want to delete a product just because I have deleted a category. I want to be able to reassign in at a later time to another category. My mappings representing the mentioned scenario are below.</p> <pre><code>&lt;?xml version="1.0" encoding="utf-8" ?&gt; &lt;hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="naakud.domain" namespace="naakud.domain"&gt; &lt;class name="Category"&gt; &lt;id name="Id"&gt; &lt;generator class="hilo" /&gt; &lt;/id&gt; &lt;version name="Version"/&gt; &lt;property name="Name" not-null="true" unique="true" /&gt; &lt;set name="Products" cascade="save-update" inverse="true" access="field.camelcase-underscore"&gt; &lt;key column="CategoryId" foreign-key="fk_Category_Product" /&gt; &lt;one-to-many class="Product" /&gt; &lt;/set&gt; &lt;many-to-one name="Parent" class="Category" column="ParentId" /&gt; &lt;set name="Children" collection-type="naakud.domain.Mappings.Collections.TreeCategoriesCollectionType, naakud.domain" cascade="all-delete-orphan" inverse="true" access="field.camelcase-underscore"&gt; &lt;key column="ParentId" foreign-key="fk_Category_ParentCategory" /&gt; &lt;one-to-many class="Category"/&gt; &lt;/set&gt; &lt;/class&gt; &lt;/hibernate-mapping&gt; &lt;?xml version="1.0" encoding="utf-8" ?&gt; &lt;hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="naakud.domain" namespace="naakud.domain"&gt; &lt;class name="Product"&gt; &lt;id name="Id"&gt; &lt;generator class="hilo" /&gt; &lt;/id&gt; &lt;version name="Version" /&gt; &lt;property name="Name" not-null="true" unique="true" /&gt; &lt;property name="Description" not-null="true" /&gt; &lt;property name="UnitPrice" not-null="true" type="Currency" /&gt; &lt;many-to-one name="Category" column="CategoryId" /&gt; &lt;/class&gt; &lt;/hibernate-mapping&gt; </code></pre> <p>With this mapping, when I delete a category which has products associated with it I get the following constraint error.</p> <p>The DELETE statement conflicted with the REFERENCE constraint "fk_Category_Product". The conflict occurred in database "naakud", table "dbo.Product", column 'CategoryId'. The statement has been terminated.</p> <p>However, when I remove the inverse=true attribute on the Products collection in the Category mapping then it works fine. My CategoryId foreign key in the products table is set to null and thus disassociating a product with a category. Which is what I want.</p> <p>I have read about the inverse attribute and I understand it signifies the owning side of a relationship and updates/inserts/deletes are done in a different order which is why I think it solves my problem. So my question is, am I solving my problem in the correct way? How does this affect performance? (not much I suspect). Would it be better to have a uni-directional relationship without the many to one side and have the inverse attribute set to true to get better performance? Or am I going crazy and completely missing the point? </p>
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