Firebase：检索实现Map< K，V>的类的值 [英] Firebase: retrieve value of class that implements Map<K, V>

问题描述

假设我有数据类：

$ $ p $ class MyDataClass {
...
public Map<字符串，对象> properties = HashMap（）
}

//稍后
MyDataClass data = snapshot.getValue（MyDataClass.class）;


运行此代码后，data.properties包含所有存在于属性键在给定的快照。

出于某种原因，我想改变类型的属性字段到我的自定义Map实现：

  class MyMap实现Map< String，Object> {...} 
 $ b $ class MyDataClass {
 ... 
 public MyMap properties = MyMap（）
} 
 
 // later 
 MyDataClass data = snapshot.getValue（MyDataClass.class）; 
  

运行此代码后，data.properties中没有数据。
$ b $我不知道是否有可能检索数据到自定义地图实现？

UPD：JSON我试图阅读

  {
 items：{
id：{
name：name，
properties ：{
simpleProp1：value1，
simpleProp2：value2，
simpleProp3：value3，
complexProp1：{
subPop1：subVal1
 ... 
} 
} 
} 
} 
} 
   
      不要以为Firebase将能够直接使用您的自定义 Map 实现。因此，您可以考虑添加一个简单的数据类： 
 
 
  class MyDataJSON {
 public MyDataJSON（）{} 
公共字符串名称; 
 public Map< String，Object>性能; 
} 
 
 class MyDataClass {
 MyDataClass（MyDataJSON json）{...} 
 ... 
} 
  MyDataClass 对象：$ b $ 
 
 
 $ b 
 b 
 
  MyDataJSON json = snapshot.getValue（MyDataJSON.class）; 
 MyDataClass data = MyDataClass（json）; 
  
我知道，远非完美，但至少您可以完全控制数据库 unmarshalling 进程（和相应的属性类型）。  
Assume I have data class:
class MyDataClass {
    ...
    public Map<String, Object> properties = HashMap()
}

// later
MyDataClass data = snapshot.getValue(MyDataClass.class);
After running this code data.properties contains all the data that exists under the properties key in the given snapshot.

For some reason I want to change type of properties field to my custom Map implementation:
class MyMap implements Map<String, Object> { ... }

class MyDataClass {
    ...
    public MyMap properties = MyMap()
}

// later
MyDataClass data = snapshot.getValue(MyDataClass.class);
After running this code data.properties no data.

I wonder if it is even possible to retrieve data to custom map implementation?

UPD: JSON i try to read
{
  items: {
    "id": {
      "name": "name",
      "properties": {
        "simpleProp1": "value1",
        "simpleProp2": "value2",
        "simpleProp3": "value3",
        "complexProp1": {
          "subPop1": "subVal1"
          ...
        }
      }
    }
  }
}
Thanks!
解决方案
I don't think Firebase will be able to work with your custom Map implementation directly. As such, you might consider adding a simple data class instead:
class MyDataJSON {
    public MyDataJSON() { }
    public String name;
    public Map<String, Object> properties;
}

class MyDataClass {
    MyDataClass(MyDataJSON json) { ... }
    ...
}
then use it to construct your MyDataClass object:
MyDataJSON json = snapshot.getValue(MyDataJSON.class);
MyDataClass data = MyDataClass(json);
I know, far from perfect, but at least you gain complete control over the database unmarshalling process (and corresponding properties types). 

                        
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