Question

我想修改数据库中某行的记录，但是不知何故出现了database is locked错误

void Bookshop::modifyBookRecords () {
    std::cout << "You want to modify a book" << std::endl;
    std::cout << "Title/ISBN: ";
    std::string input;
    std::getline (std::cin, input);
    bool isAvailable = database.checkAvailability (input);
    database.closeDb ();
    if (isAvailable) {
        std::cout << "Title: ";
        std::string title;
        std::getline (std::cin, title);
        std::cout << "Author: ";
        std::string author;
        std::getline (std::cin, author);
        std::cout << "Pages: ";
        int pages;
        std::cin >> pages;
        std::cin.ignore (std::numeric_limits<std::streamsize>::max (), '\n');
        std::cout << "Genre: ";
        std::string genre;
        std::getline (std::cin, genre);
        std::cout << "Publisher: ";
        std::string publisher;
        std::getline (std::cin, publisher);
        std::cout << "ISBN: ";
        std::string isbn;
        std::getline (std::cin, isbn);
        std::cout << "Number of Copies: ";
        int numberOfCopies;
        std::cin >> numberOfCopies;
        std::cin.ignore (std::numeric_limits<std::streamsize>::max (), '\n');
        database.updateRecord (input, title, author, pages, genre, publisher, isbn, numberOfCopies);
     }
     else {
         std::cout << "The book was not found" << std::endl;
     }
}

CheckAvailability方法

bool Database::checkAvailability (std::string& input) {
    openDb (dir);
    sqlite3_stmt* stmt;
    rc = sqlite3_prepare_v2 (db, "SELECT * FROM Books WHERE Title = ? OR Isbn = ?", -1, &stmt, NULL);
    if (rc != SQLITE_OK) {
        std::cout << sqlite3_errmsg (db);
        closeDb ();
        return false;
    }
    sqlite3_bind_text (stmt, 1, input.c_str (), input.length (), NULL);
    sqlite3_bind_text (stmt, 2, input.c_str (), input.length (), NULL);

    if (sqlite3_step (stmt) == SQLITE_ROW) {
        return true;
        sqlite3_finalize (stmt);
        sqlite3_close (db);
    }    
    else {
        return false;
        sqlite3_finalize (stmt);
        sqlite3_close (db);
    }
}

updateRecords方法

// Method updates the whole row with the values from the parameter list
void Database::updateRecord (const std::string& input,
                         const std::string& title,
                         const std::string& author,
                         const int& pages,
                         const std::string& genre,
                         const std::string& publisher,
                         const std::string& isbn,
                         const int& numberOfCopies) {
    openDb (dir);
    sqlite3_stmt* stmt;
    rc = sqlite3_prepare_v2 (db, "UPDATE Books SET Title = ?, Author = ?, Pages = ?, Genre = ?, Publisher = ?, Isbn = ?, Copies = ? WHERE Title = ? OR Isbn = ?", -1, &stmt, NULL);
    if (rc != SQLITE_OK) {
        std::cerr << sqlite3_errmsg (db);
        closeDb ();
    }
    sqlite3_bind_text (stmt, 1, title.c_str (), title.length (), NULL);
    sqlite3_bind_text (stmt, 2, author.c_str (), author.length (), NULL);
    sqlite3_bind_int (stmt, 3, pages);
    sqlite3_bind_text (stmt, 4, genre.c_str (), genre.length (), NULL);
    sqlite3_bind_text (stmt, 5, publisher.c_str (), publisher.length (), NULL);
    sqlite3_bind_text (stmt, 6, isbn.c_str (), isbn.length (), NULL);
    sqlite3_bind_int (stmt, 7, numberOfCopies);
    sqlite3_bind_text (stmt, 8, input.c_str (), input.length (), NULL);
    sqlite3_bind_text (stmt, 9, input.c_str (), input.length (), NULL);
    rc = sqlite3_step (stmt);
    if (rc != SQLITE_OK) {
        std::cerr << sqlite3_errmsg (db);
    }
    else {
        std::cout << "books was updated successfully" << std::endl;
    }
    sqlite3_finalize (stmt);
    closeDb ();
}

该错误在checkAvailability方法中的某处，因为当我删除它时，一切正常。有人告诉我，数据库在某处打开，因此以后不允许在该方法中打开它。但是我在checkAvailability（）结尾时关闭了数据库，所以我不知道问题所在。

Answer 1

要从checkAvailability返回，然后再关闭数据库。从函数返回后，不会执行return语句之后的语句。控制流返回到函数的调用者。

bool Database::checkAvailability (std::string& input) {
    openDb (dir);
    sqlite3_stmt* stmt;
    rc = sqlite3_prepare_v2 (db, "SELECT * FROM Books WHERE Title = ? OR Isbn = ?", -1, &stmt, NULL);
    if (rc != SQLITE_OK) {
        std::cout << sqlite3_errmsg (db);
        closeDb ();
        return false;
    }
    sqlite3_bind_text (stmt, 1, input.c_str (), input.length (), NULL);
    sqlite3_bind_text (stmt, 2, input.c_str (), input.length (), NULL);

    if (sqlite3_step (stmt) == SQLITE_ROW) {
        sqlite3_finalize (stmt);
        sqlite3_close (db);
        return true;
    }    
    else {
        sqlite3_finalize (stmt);
        sqlite3_close (db);
        return false;
    }
}

SQLite3 C ++数据库已锁定

1 个答案: