Zimogorov_Arseniy_OrdersManager/AddExemplarsForm.cs

using Npgsql;
using System;
using System.Configuration;
using System.Data;
using System.Windows.Forms;

namespace WindowsFormsApp4
{
    public partial class AddExemplarsForm : Form
    {
        private readonly string connStr = ConfigurationManager.ConnectionStrings["PostgreSQL"].ConnectionString;
        private int selectedBookId = 0;

        public AddExemplarsForm()
        {
            InitializeComponent();
        }

        private void AddExemplarsForm_Load(object sender, EventArgs e)
        {
            if (Session.LibraryId == null)
            {
                MessageBox.Show("Ошибка: ваша учётная запись не привязана к библиотеке. Обратитесь к администратору.", "Ошибка");
                this.Close();
                return;
            }
            LoadBooks();
        }

        private void LoadBooks()
        {
            string query = @"
                SELECT b.id, b.title || ' (' || a.name || ' ' || a.lastname || ')' AS book_display
                FROM book b
                JOIN authors a ON b.author_id = a.id
                ORDER BY b.title";
            DataTable dt = new DataTable();
            using (var conn = new NpgsqlConnection(connStr))
            using (var da = new NpgsqlDataAdapter(query, conn))
            {
                da.Fill(dt);
            }
            cmbBook.DisplayMember = "book_display";
            cmbBook.ValueMember = "id";
            cmbBook.DataSource = dt;
            cmbBook.SelectedIndex = -1;
        }

        private void cmbBook_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (cmbBook.SelectedValue == null)
                selectedBookId = 0;
            else
                selectedBookId = (int)cmbBook.SelectedValue;
        }

        private void btnAdd_Click(object sender, EventArgs e)
        {
            if (selectedBookId == 0)
            {
                MessageBox.Show("Выберите книгу.", "Ошибка", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;
            }
            int newCount = (int)numericNewCount.Value;
            if (newCount <= 0)
            {
                MessageBox.Show("Количество должно быть больше нуля.", "Ошибка", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;
            }
            if (Session.LibraryId == null)
            {
                MessageBox.Show("Ошибка: идентификатор библиотеки не определён.", "Ошибка");
                return;
            }
            int libraryId = Session.LibraryId.Value;

            try
            {
                using (var conn = new NpgsqlConnection(connStr))
                {
                    conn.Open();
                    using (var tran = conn.BeginTransaction())
                    {
                        long nextIsbn = 1000000000;
                        string maxIsbnQuery = "SELECT COALESCE(MAX(isbn), 0) FROM book_exemplar";
                        using (var cmd = new NpgsqlCommand(maxIsbnQuery, conn, tran))
                        {
                            object max = cmd.ExecuteScalar();
                            if (max != DBNull.Value && Convert.ToInt64(max) >= nextIsbn)
                                nextIsbn = Convert.ToInt64(max) + 1;
                        }

                        for (int i = 0; i < newCount; i++)
                        {
                            string insertExemplar = @"
                                INSERT INTO book_exemplar (isbn, book_id, status, library_id)
                                VALUES (@isbn, @bookId, 'available', @libId)";
                            using (var cmd = new NpgsqlCommand(insertExemplar, conn, tran))
                            {
                                cmd.Parameters.AddWithValue("isbn", nextIsbn + i);
                                cmd.Parameters.AddWithValue("bookId", selectedBookId);
                                cmd.Parameters.AddWithValue("libId", libraryId);
                                cmd.ExecuteNonQuery();
                            }
                        }

                        string updateBook = "UPDATE book SET count = count + @add WHERE id = @id";
                        using (var cmd = new NpgsqlCommand(updateBook, conn, tran))
                        {
                            cmd.Parameters.AddWithValue("add", newCount);
                            cmd.Parameters.AddWithValue("id", selectedBookId);
                            cmd.ExecuteNonQuery();
                        }

                        tran.Commit();
                        MessageBox.Show($"Успешно добавлено экземпляров: {newCount}.", "Успех", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        this.DialogResult = DialogResult.OK;
                        this.Close();
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show($"Ошибка: {ex.Message}", "Ошибка", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }

        private void btnCancel_Click(object sender, EventArgs e)
        {
            this.DialogResult = DialogResult.Cancel;
            this.Close();
        }
    }
}