尝试在Firebase数据库中保存对象时出现错误“失败的绑定交易”

Question

问题出在setValue（loanedBooks）。在添加此行之前，它工作得很好。 我已经标记了有问题的行。

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if(requestCode == RC_SIGN_IN){
        if(resultCode == RESULT_OK){
            //user logged in
            Log.d("AUTH",auth.getCurrentUser().getEmail());
            UserInfo user = auth.getCurrentUser();
            database.child("users").child(user.getUid()).child("name").setValue(user.getDisplayName());

            LoanedBooks loanedBooks = new LoanedBooks();
            **database.child("users").child(user.getUid()).child("loaned books").setValue(loanedBooks);** //this is the problem

            startActivity(intent_registered);

        }
        else{
            //user not authenticated
            Log.d("AUTH","NOT AUTHENTICATED");
        }
    }

}

LoanedBooks.java类：

public class LoanedBooks {
   public ArrayList<AddBook> loanedBooks_list;
   DatabaseReference database;

   public LoanedBooks(){
       loanedBooks_list = new ArrayList<AddBook>();
       database = FirebaseDatabase.getInstance().getReference();;
   }

   public ArrayList<AddBook> getLoanedBooksList(){
       return loanedBooks_list;
   }

   public void addBook(AddBook book){
       loanedBooks_list.add(book);
   }
}

错误：

E/JavaBinder: !!! FAILED BINDER TRANSACTION !!!
E/AndroidRuntime: Error reporting crash
                  android.os.TransactionTooLargeException

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