private void SaveButton_Click(object sender, EventArgs e) { if (string.IsNullOrWhiteSpace(StudentComboBox.Text) || string.IsNullOrWhiteSpace(BookComboBox.Text)) { MessageBox.Show(@"Inputs are empty!", @"Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } else { var borrowingStudent = _students.ReadStudent(StudentComboBox.Text); var borrowedBook = _books.ReadBook(BookComboBox.Text); var dateOfBorrow = BorrowDatePicker.Value; var available = borrowedBook.NumberOfBooks; var alreadyRented = 0; foreach (var borrow in _borrows.GetBorrowsList().Where(borrow => borrow.ReturnDate == null)) { if (borrow.BookId == borrowedBook.BookId) { available--; } if (borrow.StudentId == borrowingStudent.StudentId) { alreadyRented++; } } if (alreadyRented > 2) { MessageBox.Show(@"Student passed book limit!", @"Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } else if (available < 1) { MessageBox.Show(@"No books available!", @"Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } else { _borrows.CreateBorrow(borrowingStudent, borrowedBook, dateOfBorrow); Close(); } } }