title: How to call observable that loads additional contents to a object transforming it in another observable?
body: <p>I have this <code>MyCollectionInteractor</code> that loads all <code>CollectionItemVO</code> from a firebase database:</p>
  
  <pre><code>public interface MyCollectionInteractor extends BaseInteractor{
      Single&lt;List&lt;CollectionItemVO&gt;&gt; load ();
  }
  </code></pre>
  
  <p>CollectionItemVO is:</p>
  
  <pre><code>public class CollectionItemVO {
      String beerId;
      long timestamp;
      int quantity;
  
      public CollectionItemVO() {
      }
  
  
      public CollectionItemVO(String beerId, long timestamp, int quantity) {
          this.beerId = beerId;
          this.timestamp = timestamp;
          this.quantity = quantity;
      }
  }
  </code></pre>
  
  <p>So I have this <code>CollectionItem</code>:</p>
  
  <pre><code>public class CollectionItem {
  
      private final CollectionItemVO itemVOList;
      private final Beer beer;
  
      public CollectionItem(Beer beer, CollectionItemVO itemVOList) {
          this.beer = beer;
          this.itemVOList = itemVOList;
      }
  
  }
  </code></pre>
  
  <p>That has a complete Beer object. To load that object I use this other interactor:</p>
  
  <pre><code>public interface LoadBeerInteractor extends BaseInteractor {
      Flowable&lt;Beer&gt; load(String beerId);
  }
  </code></pre>
  
  <p>I want to transform this <code>CollectionInteractor.load</code> call into an <code>Observable</code> that emits <code>CollectionItem</code> and I want to use <code>LoadBeerInteractor.load(beerId)</code> to delivery CollectionItem with full beer object. </p>
  
  <p>For what I studied, I believe it is possible to do that using flatmap but I have not been able to achieve the desired result yet.</p>