java - How to read and write data in 2 different child at the same time in Firebase -

i trying develop android app need send data firebase db having it's schema mentioned below:

 {     "usercart": {         "unique_id": {              "book": [                   "book_id1" : {                      "book_title": "abc",                      "book_url": "imageurl",                      "chapters_purchased": [ // multiple chapters                            "chapter_3": {                                "chapter_title":"title3",                                "chapter_page_count":"16"                            },                            "chapter_4": {                                "chapter_title":"title4",                                "chapter_page_count":"18"                            }                                           ]                   },                    "book_id2" : {                      "book_title": "pqr",                      "book_url": "imageurl2",                      "chapters_purchased": [ // multiple chapters                            "chapter_5": {                                "chapter_title":"title3",                                "chapter_page_count":"16"                            },                            "chapter_9": {                                "chapter_title":"title4",                                "chapter_page_count":"18"                            }                                           ]                   }                ]        }  } 

i have bookdetailactivity, in i'm showing chapters in recyclerview. so, can "unique_id" & "book_id" bookdetailactivity. after clicking on chapters' recyclerview, need send values specified in above schema.

also, need retrieve values in activity.

the java code mentioned chapters' recyclerview, present in bookdetailactivity mentioned below:

  firebaserecycleradapter<chapters, chapterholder> chapter_name_adapter = new firebaserecycleradapter<chapters, chapterholder>(             chapters.class,             r.layout.simple_chapters_horizontal_list,             chapterholder.class,             refforbookname.child("chapter")) {         @override         protected void populateviewholder(chapterholder viewholder, final chapters model, final int position) {             viewholder.setchaptername(model.gettitle());             viewholder.buy_or_view_botton.setonclicklistener(new view.onclicklistener() {                 @override                 public void onclick(view v) {                      databasereference refforcart = firebasedatabase.getinstance().getreference().child("usercart").child(uniqueid + "").child("book");                      calendar c = calendar.getinstance();                     system.out.println("current time => " + c.gettime());                     simpledateformat df = new simpledateformat("dd-mm-yyyy hh:mm:ss");                      string formatteddate = df.format(c.gettime());                     bookcartofchapters bookcartofchapters = new bookcartofchapters();                     bookcartofchapters.setbookurl(bookimageurl);                     bookcartofchapters.setbooktitle(booktitle);                     chapters_purchased chapters = new chapters_purchased();                     chapters.setchapter_title(model.gettitle());                     chapters.setdatetime(formatteddate);                     chapters.setpage_count(model.getpage_count());                     chapters.setprice(model.getprice());                     chapters_purchased.add(chapters);                     bookcartofchapters.setchapters_purchased(chapters_purchased);                      //refforcart.child(bookid+"").setvalue(book);                     refforcart.child(bookid + "").setvalue(bookcartofchapters);                 }             });              viewholder.chapterslayout.setonclicklistener(new view.onclicklistener() {                 @override                 public void onclick(view v) {                     intent tochaptersactivity = new intent(bookdetailactivity.this, folioactivity.class);                     tochaptersactivity.putextra(folioactivity.intent_epub_source_type, folioactivity.epubsourcetype.assets);                     tochaptersactivity.putextra(folioactivity.intent_epub_source_path, "epub/one amazing thing - chitra banerjee divakaruni.mobi");                     startactivity(tochaptersactivity);                 }             });          }     }; 

help me in achieving same.