title: in ObjectBox, using ToMany vs using my own list of string ids in managing relations?
body: <p>Take the example from the documentation, using ToMany relations:</p>
  <pre><code>@Entity
  public class Customer {
      @Id public long id;
      
      // 'to' is optional if only one relation matches.
      @Backlink(to = &quot;customer&quot;)
      public ToMany&lt;Order&gt; orders;
      
  }
  
  @Entity
  public class Order {
      @Id public long id;
      
      String stringId;
      ...
  }
  </code></pre>
  <p>where stringId in order is a long string like &quot;CS-DE-AA-order1234567890&quot;.</p>
  <p>For the same purpose, if I keep a list of string ids and manage them myself, it would be like:</p>
  <pre><code>@Entity
  public class Customer {
      @Id public long id;
      
      String orderIds;
  }
  </code></pre>
  <p>where orderIds keeps Orders' stringId separated by space, like:
  &quot;CS-DE-AA-order1234567891 CD-DF-AB-order1234567891 CT-SE-BB-order1234567892 ...&quot;</p>
  <p>So I would like to know how the two schemes compare in terms of performance, efficiency and disk storage.</p>