title: JPA @OneToMany is not working when result is list
body: <p>I'm working with JPA, Spring boot.
  Using @OneToMany annotation, when I fetch orders containing cart items.
  My domain codes are below.</p>
  
  <p>Order:</p>
  
  <pre><code>@Data
  @Entity
  @Table(name="\"order\"")
  @ToString
  public class Order {
  
      @Id
      @GeneratedValue
      @Getter @Setter
      private Long id;
  
      @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true)
      @JoinColumn(name="order_id")
      @Getter @Setter
      private List&lt;Cart&gt; carts;
  
      public void addCart(Cart cart) {
          if (this.carts == null) {
              carts = new ArrayList&lt;Cart&gt;();
          }
          carts.add(cart);
      }
  }
  </code></pre>
  
  <p>Cart:</p>
  
  <pre><code>@Data
  @Entity
  @Table(name="cart")
  @ToString
  public class Cart {
  
      @Id
      @GeneratedValue
      @Getter @Setter
      @Column(name="id")
      private Long id;
  
      @Column(name = "order_id")
      @Getter @Setter
      private Long orderId;
  
  }
  </code></pre>
  
  <p>This works very well when I fetch only one order, but doesn't work when I fetch more than two orders. I mean when I fetch only one order, carts field's size is 1 or more, but when I fetch two or more orders, the carts field's size is 0.</p>
  
  <p>How can I solve this problem? Thank you in advance!</p>