Firebase查询 - 访问Firebase Android中的嵌套对象

Question

I have a firebase object that looks like this

posts: {
  -Kc6CT_CF--kVYApIhD9: {
    -comments: {
       -Kc6CkgQ8-5OztuqHqdS {
         text: "Text here",
         timestamp: 1486179732382,
         user: {
              "username": "user1",
              "email": "some@email.com"
         }
       }
    },
    "lat": "37.8136",
    "lng": "144.9631"
  }
}

And I have a POJO that looks like this:

public class Post {

    private Comment comments;
    private double lat;
    private double lng;
    private String text;
    private String timestamp;
    private Motorist user;


    public Post() {  }

    public Comment getComments() {
        return comments;
    }

    public void setComments(Comment comments) {
        this.comments = comments;
    }

    public double getLat() {
        return lat;
    }

    public void setLat(double lat) {
        this.lat = lat;
    }

    public double getLng() {
        return lng;
    }

    public void setLng(double lng) {
        this.lng = lng;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public String getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(String timestamp) {
        this.timestamp = timestamp;
    }

    public Motorist getUser() {
        return user;
    }

    public void setUser(Motorist user) {
        this.user = user;
    }

    public static class Comment {

        String text;
        String timestamp;
        Motorist user;

        public String getText() {
            return text;
        }

        public void setText(String text) {
            this.text = text;
        }

        public String getTimestamp() {
            return timestamp;
        }

        public void setTimestamp(String timestamp) {
            this.timestamp = timestamp;
        }

        public Motorist getUser() {
            return user;
        }

        public void setUser(Motorist user) {
            this.user = user;
        }
    }
}

Here's the code where I loop in my posts object:

Map<String, Post> td = new HashMap<String, Post>();
    for(DataSnapshot postSnapshot : dataSnapshot.getChildren()){

        Post post = postSnapshot.getValue(Post.class);

        //for (DataSnapshot commentSnapshot : postSnapshot.child("comments").getChildren()) {
        //    System.out.println(commentSnapshot.getValue());
        //}

        td.put(postSnapshot.getKey(), post);
        Toast.makeText(MapsActivity.this, postSnapshot.getValue().toString(), Toast.LENGTH_SHORT).show();
    }

I am using the addValueEventListener . Now, my problem is I cant get the data in comments object. When I run the debugger my comments object is null . What am I missing? Or is there something wrong with my POJO?

Answer 1

There are a few problems in your code and data structure:

-comments: {
   -Kc6CkgQ8-5OztuqHqdS {
     text: "Text here",
     timestamp: 1486179732382,
     user: {
          "username": "user1",
          "email": "some@email.com"
     }
   }

If that - is indeed in front of comments , please remove it. The node should just be called comments and adding a - prefix just makes it more difficult to handle correctly.

Next up is a problem in your code: under (now) comments you have a list of comments, keyed by a push ID (the keys starting with -K . In your code you've only modeled a single comment:

public class Post {
    private Comment comments;

There is no way that the Firebase Database client can map all child nodes of comments into that single Comment , so it skips it when it reads the JSON. The correct mapping of your JSON structure is:

public class Post {
    public Map<String,Comment> comments;

If you then only want to handle the values of the comments, you can get them with post.comments.values() .