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POOrder by both Parent and then Child using JPA
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  1. POOrder by both Parent and then Child using JPA
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    copied!<p>Is it possible to order a collection of parent objects by both a parent's property and a child's property?</p> <p>Let's say I have an Entity class that has this bit of code:</p> <pre><code>@OrderBy("age") public List&lt;Father&gt; getFathers() { return fathers; } </code></pre> <p>The Father Entity has an age property which we want to order by ascending age (as shown above).</p> <p>A Father can have a Child. A Child would also have an age property. I would like <code>getFathers()</code> to return a Fathers list such that they are ordered by the Fathers' age and then subsequently the Child's age ascending. </p> <p>If I keep the code above as is, the Fathers would be ordered by their own age correctly but a Father (aged 30) with a 10 year old Child could come before a Father (also aged 30) with a 5 year old Child.</p> <p>I tried doing something like this:</p> <pre><code>@OrderBy("age, child.age") public List&lt;Father&gt; getFathers() { return fathers; } </code></pre> <p>But I would get the following exception:</p> <pre><code>org.hibernate.AnnotationException: property from @OrderBy clause not found: Father.child.age </code></pre> <p><b>Edit:</b> Sorry, let me clarify with a bit more code. The <code>getFathers()</code> is not in the Child entity but in another entity. Let's call it Village:</p> <pre><code>@Entity public class Village { ... @OneToMany(mappedBy = "village", targetEntity = Father.class) @OrderBy("age") public List&lt;Father&gt; getFathers() { return fathers; } } </code></pre> <p>So let's say there is a Village and you can obtain the Fathers that live in this Village. For this example's sake, let's say that a Father for some odd Village rule can only have one child each.</p> <p>So Father would look something like this:</p> <pre><code>@Entity public class Father { private Child child; ... @OneToOne(mappedBy = "father") public Child getChild() { return child; } public void setChild(Child child) { this.child = child; } } </code></pre> <p>So now in the original Village class, I want <code>getFathers()</code> to return all the fathers in order of age, plus, if there are any fathers with the same age, I want them to be then ordered by the age of their child.</p> <p><b>Edit 2:</b> I've also found that I can get the effect of what I want however it can't be the most elegant way of doing it:</p> <pre><code>session.createFilter(village.getFathers(), "order by child.age"); </code></pre>
 

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