How To Retrieve Correct Subtype From Firebase Android Getvalue()

Hi all I can't think of a better example to illustrate my point so do let me know If my example has some errors. But hopefully this example will get my point through. class A {

Solution 1:

If you use Firebase's default serializer, it simply writes all public properties and fields to the database. Say that you store a single instance of each class, it'd be:

-L1234567890: {
  cATEGORY: "A"
},
-L1234567891: {
  cATEGORY: "B"
},
-L1234567892: {
  cATEGORY: "C"
},

There won't be enough knowledge in the database for the SDK to reinflate the correct sub-class. While you and I can see that the cATEGORY value matches the class name, the Firebase SDK has no such knowledge.

It won't be too hard to write your own custom deserializer for this data though, taking a DataSnapshot with the values above and reinflating the correct class and values.

You could also do a hybrid: detect the class type directly, and then tell Firebase what class to read:

String cat = snapshot.child("cATEGORY").getValue(String.class)
Class clazz = "C".equals(cat) ? C.class : "B".equals(cat) ? B.class : A.clas;
A object = snapshot.getValue(clazz);