subscribeToDbChanges.java

private void subscribeToDbChanges() {
        // как преобразовать LiveData
        // входная сигнатура - List<LoanWithUserAndBook>
        // выходная - String
        LiveData<List<LoanWithUserAndBook>> loans
                = mDb.loanModel().findLoansByNameAfter("Alexander", getYesterdayDate());

        // Instead of exposing the list of Loans, we can apply a transformation and expose Strings.
        mLoansResult = Transformations.map(loans,
                new Function<List<LoanWithUserAndBook>, String>() {
                    @Override
                    public String apply(List<LoanWithUserAndBook> loansWithUserAndBook) {
                        StringBuilder sb = new StringBuilder();
                        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm",
                                Locale.US);

                        for (LoanWithUserAndBook loan : loansWithUserAndBook) {
                            sb.append(String.format("%s\n  (Returned: %s)\n",
                                    loan.bookTitle,
                                    simpleDateFormat.format(loan.endTime)));
                        }
                        return sb.toString();
                    }
                });
    }