evaluationenginehierarchies.html

---
layout: documentation 
title: EvaluationEngine 
teaser: Decouple business logic from control flow
navigation:
   - name: Overview
     link: evaluationengine.html
   - name: Tutorial
     link: evaluationenginetutorial.html	
   - name: Modules
     link: evaluationenginemodules.html
   - name: Hierarchical Evaluation Engines
     link: evaluationenginehierarchies.html
   - name: Aggregators
     link: evaluationengineaggregators.html
   - name: Expressions
     link: evaluationengineexpressions.html
   - name: Strategies
     link: evaluationenginestrategies.html
   - name: Validation
     link: evaluationenginevalidation.html
   - name: Logging
     link: evaluationenginelogging.html
   - name: Tips and Tricks
     link: evaluationenginetipsandtricks.html
   - name: Specifications
     link: evaluationenginespecifications.html		 
---
<h2>Hierarchical Evaluation Engines</h2>
<p>
An evaluation engine can have a parent evaluation engine:
</p>
<script type="syntaxhighlighter" class="brush: csharp"><![CDATA[
var parentEngine = new EvaluationEngine();
var childEngine = new EvaluationEngine(parentEngine);
]]></script>
<p>
When you ask the child engine a question, it will use all the expressions of the parent and the child.
When you ask the parent engine, it will only use the expressions known to the parent.
</p>
<p>
If the child engine defines an aggregator, the child aggregator will be used when asking a question on the child. Thus overriding the parent aggregator.
</p>