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POSimple NHibernate Eager Loading confusion
 

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  1. POSimple NHibernate Eager Loading confusion
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    <p>I have a very simple master-child model: </p> <p><strong>WorkflowEscalationPolicy&lt;--WorkflowEscalation</strong>. </p> <p>The WorkflowEscalations are accessible from the <code>WorkflowEscalationPolicy.Escalations</code> property.</p> <p>I want to eagerly fetch the escalations when I get the <code>WorkflowEscalationPolicy</code> items.</p> <p>I have a method that gets all escalation policies. I have tried using this:</p> <pre><code>IEnumerable&lt;IWorkflowEscalationPolicy&gt; results = Session .Query&lt;WorkflowEscalationPolicy&gt;() .Fetch(x=&gt;x.Escalations) .Where(q=&gt;q.ApplicationKey==applicationKey); </code></pre> <p>and this:</p> <pre><code>IEnumerable&lt;IWorkflowEscalationPolicy&gt; results = Session .CreateCriteria&lt;WorkflowEscalationPolicy&gt;() .SetFetchMode("Escalations", FetchMode.Eager) .List&lt;WorkflowEscalationPolicy&gt;(); </code></pre> <p>to accomplish this, but neither work - in that the child Escalations collection remains empty. I know that there are <code>WorkflowEscalations</code> in the database.</p> <p>My mapping files:</p> <pre><code>&lt;hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="FB.SimpleWorkflow.NHibernate" namespace="FB.SimpleWorkflow.NHibernate.Model" &gt; &lt;class name="WorkflowEscalationPolicy" table="SW_WorkflowEscalationPolicy" &gt; &lt;id name="Id"&gt; &lt;generator class="native" /&gt; &lt;/id&gt; &lt;property name="ApplicationKey" /&gt; &lt;property name="ActivityKey" /&gt; &lt;property name="InstanceKey" /&gt; &lt;property name="State" /&gt; &lt;property name="EscalateAfterSeconds" /&gt; &lt;property name="MaximumEscalationsPerTransition" /&gt; &lt;set name="Escalations" table="SW_WorkflowEscalation" cascade="all-delete-orphan" inverse="true"&gt; &lt;key column="WorkflowEscalationPolicyId" /&gt; &lt;one-to-many class="WorkflowEscalation" /&gt; &lt;/set&gt; &lt;/class&gt; &lt;/hibernate-mapping&gt; &lt;hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="FB.SimpleWorkflow.NHibernate" namespace="FB.SimpleWorkflow.NHibernate.Model" &gt; &lt;class name="WorkflowEscalation" table="SW_WorkflowEscalation" &gt; &lt;id name="Id"&gt; &lt;generator class="native" /&gt; &lt;/id&gt; &lt;property name="EscalatedTimeStamp" /&gt; &lt;property name="EscalatedByUserName" /&gt; &lt;property name="EscalatedOnHost" /&gt; &lt;many-to-one name="WorkflowEscalationPolicy" column="WorkflowEscalationPolicyID" /&gt; &lt;many-to-one name="WorkflowActivityInstanceTransition" column="WorkflowActivityInstanceTransitionId" /&gt; &lt;/class&gt; &lt;/hibernate-mapping&gt; </code></pre> <p>What is the difference between the two and what am I missing here? I thought that in the first instance NHibernate refers to the mapping files for loading strategies?</p> <p>NHibernate is v3.1</p> <h2><strong>Update: 6 June 2013</strong></h2> <p>Further investigations thanks to @cremor ...</p> <p>I've profiled the generated SQL that the query executes and I get:</p> <pre><code>SELECT this_.Id as Id4_1_, this_.ApplicationKey as Applicat2_4_1_, this_.ActivityKey as Activity3_4_1_, this_.InstanceKey as Instance4_4_1_, this_.State as State4_1_, this_.EscalateAfterSeconds as Escalate6_4_1_, this_.MaximumEscalationsPerTransition as MaximumE7_4_1_, escalation2_.WorkflowEscalationPolicyID as Workflow5_3_, escalation2_.Id as Id3_, escalation2_.Id as Id2_0_, escalation2_.EscalatedTimeStamp as Escalate2_2_0_, escalation2_.EscalatedByUserName as Escalate3_2_0_, escalation2_.EscalatedOnHost as Escalate4_2_0_, escalation2_.WorkflowEscalationPolicyID as Workflow5_2_0_, escalation2_.WorkflowActivityInstanceTransitionID as Workflow6_2_0_ FROM SW_WorkflowEscalationPolicy this_ left outer join SW_WorkflowEscalation escalation2_ on this_.Id=escalation2_.WorkflowEscalationPolicyID </code></pre> <p>Which is what I would expect.</p> <p>This generates the correct SQL, with the single detail Escalation record to the right of the master EscalationPolicy record. Therefore, the database is fine, the T-SQL is fine and therefore there is a misunderstanding within the NHibernate somewhere.</p>
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    1. COWhat exactly does not work? Eager loading only means that the Escalations list is loaded directly after the the WorkflowEscalationPolicy object and does not mean that some join is executed.
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    2. COSorry, have added clarification. The Escalations property (of WorkflowEscalation) is empty even though there are records in the database. Maybe that's what I'm not clear on? However, I have seen this code work before! Something has changed and I accept I've broken it but need to figure out how :)
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