title: JPA Persist parent and child with one to many relationship
body: <p>I want to persist parent entity with 20 child entities, 
  my code is below</p>
  
  <p>Parent Class</p>
  
  <pre><code>@OneToMany(mappedBy = "parentId")
  private Collection&lt;Child&gt; childCollection;
  </code></pre>
  
  <hr>
  
  <p>Child Class</p>
  
  <pre><code>@JoinColumn(name = "parent_id", referencedColumnName = "parent_id")
  @ManyToOne(optional=false)
  private Parent parent;
  </code></pre>
  
  <hr>
  
  <pre><code>String jsonString = "json string containing parent properties and child  collection" 
  
  ObjectMapper mapper = new ObjectMapper();
  Parent parent = mapper.readValue(jsonString, Parent.class);
  
  public void save(Parent parent) {
      Collection&lt;Child&gt; childCollection = new ArrayList&lt;&gt;() ;
  
      for(Child tha : parent.getChildCollection()) { 
          tha.setParent(parent);
          childCollection.add(tha);
      }
  
      parent.setChildCollection(childCollection);
      getEntityManager().persist(parent);
   }
  </code></pre>
  
  <p>So if there are 20 child tables then I have to set parent reference in each of them for that I have to write 20 for loops?
   Is it feasible? is there any other way or configuration where I can automatically persist parent and child?</p>