title: Jackson: Can not handle managed/back reference 'defaultReference' with nested DTOs
body: <p>recently with these two DTO I got this error</p>
  
  <blockquote>
    <p>MappingJackson2HttpMessageConverter:163 - Failed to evaluate Jackson
    deserialization for type [simple type, class seml.dto.PoiDto]:
    java.lang.IllegalArgumentException: Can not handle managed/back
    reference 'defaultReference': back reference type (java.util.Set) not
    compatible with managed type (seml.dto.ConceptDto)</p>
  </blockquote>
  
  <p>As you can see in the code below, I have a Set of ConceptDto objects, that have respectively some sets of broaders/narrowers/relateds ConceptDto object. Surely I was wrong to use @JsonManagedReference/@JsonBackReference but I don't understand how. 
  Can anybody help me with this issue? Thanks to everyone.</p>
  
  <p>PoiDto.java</p>
  
  <pre><code>public class PoiDto extends GenericDto&lt;String&gt;{
  
      private String id;
      private String uri;
      private String title = "";
      private String description = "";
  
      @JsonManagedReference
      private Set&lt;ConceptDto&gt; concepts = new HashSet&lt;ConceptDto&gt;();
  
      @JsonManagedReference
      @JsonBackReference
      private Set&lt;PoiDto&gt; relatedPOIs = new HashSet&lt;PoiDto&gt;();
  
      private Set&lt;ProductOrServiceDto&gt; relatedProductOrServices = new HashSet&lt;ProductOrServiceDto&gt;();
  [...]
  </code></pre>
  
  <p>ConceptDto.java</p>
  
  <pre><code>public class ConceptDto extends GenericDto&lt;String&gt; {
  
      private String prefLabelIt;
      private String prefLabelEn;
      private String code;
      private double rating;
  
  
      @JsonBackReference
      private Set&lt;ConceptDto&gt; broaders = new HashSet&lt;ConceptDto&gt;();
  
      @JsonManagedReference
      private Set&lt;ConceptDto&gt; narrowers = new HashSet&lt;ConceptDto&gt;();
  
      @JsonIgnore
      private Set&lt;ConceptDto&gt; relateds = new HashSet&lt;ConceptDto&gt;();
  
  [...]
  </code></pre>