领域或更新的领域顺序

Question

我正在使用Realm来持久化Android项目的对象.问题是我有许多类和内部字段的组合作为类和列表.就像是

class A extends RealmObject{
   @PrimaryKey long id;
   B b;
} 

class B extends RealmObject{
   @PrimaryKey long id;
   RealmList<C> cList;
}

class C extends RealmObject{
  @PrimaryKey long id;
  Date date;
  String value;
  //other fields....
}

问题是,我想更新一些领域的ç或插入新ç在B的RealmList.我应该以什么顺序这样做以保持关系？谁能举一个真实的例子？此外,Realm不支持ID的自动增量,目前我在启动时将它们设置为currentTimeInMillis.还有更好的选择吗？

Answer 1

让您的模型类成为

class A extends RealmObject{
   @PrimaryKey
   private long id;
   private B b;

   public A(){
       //required empty constructor
   }

   public A(long id){
       this.id = id;
   }

   public B getB(){
       return b;
   }

   public void setB(B b){
       this.b = b;
   }
} 

class B extends RealmObject{
   @PrimaryKey
   private long id;
   private RealmList<C> cList = new RealmList<>();

   public B(){
       //required empty constructor
   }

   public B(long id){
   this.id = id;
   }

   public RealmList<C> getCList(){
       return cList;
   }

   public void setCList(RealmList<C> cList){
       this.cList = cList;
   }
}

class C extends RealmObject{
  @PrimaryKey 
  private long id;
  private Date date;
  private String value;
  //other fields....

  public C(){
      //required empty constructor
  }

  public C(long id){
      this.id = id;
  }
}

示例-1：创建新对象并根据层次结构进行分配

    Realm realm = Realm.getDefaultInstance();
    realm.beginTransaction();

    C c = new C(id);
    realm.insertOrUpdate(c);

    B b = new B(id);
    RealmList<C> list = b.getcList();
    list.add(c);
    realm.insertOrUpdate(b);

    A a = new A(id);
    a.setB(b);
    realm.insertOrUpdate(a);
    realm.commitTransaction();

示例-2：更新数据库中的现有条目

    C c = realm.where(C.class).equalTo("id", id).findFirst();
    realm.beginTransaction();
    c.setValue("New Value"); //setter method for value
    c.insertOrUpdate();
    //while updating the existing entry in the database, you need not worry about the hierarchy, Realm will maintain the same hierarchy for updates
    //If you want to copy the existing entry from one object to another, you can use combination of method-1 and method-2
    realm.commitTransaction();