C++ code to interact with the database

Creating the PostgreSQL Database and Tables

Create the PostgreSQL database and the required tables.

Connect to your PostgreSQL instance:
```
psql -U your_username -d your_dbname
```

Create the tables:

CREATE TABLE urls (
    id SERIAL PRIMARY KEY,
    url TEXT NOT NULL,
    last_checked TIMESTAMP NOT NULL
);

CREATE TABLE content (
    id SERIAL PRIMARY KEY,
    url_id INTEGER REFERENCES urls(id),
    content TEXT,
    last_checked TIMESTAMP
);

C++ Code to Interact with PostgreSQL Database

C++ application to perform the necessary tasks. You will need the PostgreSQL client library libpqxx to interact with the database.

Install the libpqxx library:
On Ubuntu:
```
sudo apt-get update
sudo apt-get install libpqxx-dev
```
On other systems, you might need to install it via the package manager or from source.

Create fetch.cpp:

#include <iostream>
#include <pqxx/pqxx>
#include <thread>
#include <chrono>
#include <ctime>

void fetch_and_update(pqxx::connection& C) {
    while (true) {
        try {
            pqxx::work W(C);

            std::string query = "SELECT id, url FROM urls WHERE last_checked < NOW() - INTERVAL '24 hours' LIMIT 1;";
            pqxx::result R = W.exec(query);

            if (R.empty()) {
                std::cout << "No URLs found. Sleeping for 1 minute." << std::endl;
                std::this_thread::sleep_for(std::chrono::minutes(1));
                continue;
            }

            for (auto row: R) {
                int id = row["id"].as<int>();
                std::string url = row["url"].as<std::string>();

                std::cout << "Fetching URL: " << url << std::endl;

                // Placeholder for fetching content
                std::string fetched_content = "<html>Example content</html>";

                std::string content_query = "INSERT INTO content (url_id, content, last_checked) VALUES (" + W.quote(id) + ", " + W.quote(fetched_content) + ", NOW()) ON CONFLICT (url_id) DO UPDATE SET content=EXCLUDED.content, last_checked=NOW();";
                W.exec(content_query);

                std::string update_query = "UPDATE urls SET last_checked = NOW() WHERE id = " + W.quote(id) + ";";
                W.exec(update_query);

                W.commit();
            }
        } catch (const std::exception& e) {
            std::cerr << e.what() << std::endl;
        }
    }
}

int main(int argc, char* argv[]) {
    const std::string connection_str = "dbname=your_dbname user=your_username password=your_password hostaddr=127.0.0.1 port=5432";

    try {
        pqxx::connection C(connection_str);
        if (C.is_open()) {
            std::cout << "Connected to " << C.dbname() << std::endl;
            fetch_and_update(C);
        } else {
            std::cerr << "Can't open database" << std::endl;
            return 1;
        }
    } catch (const std::exception& e) {
        std::cerr << e.what() << std::endl;
        return 1;
    }
    return 0;
}

CMakeLists.txt

Create a CMakeLists.txt file to build the project.

cmake_minimum_required(VERSION 3.10)
project(fetch_service)

set(CMAKE_CXX_STANDARD 11)
find_package(PkgConfig REQUIRED)
pkg_check_modules(PQXX REQUIRED libpqxx)

include_directories(${PQXX_INCLUDE_DIRS})
link_directories(${PQXX_LIBRARY_DIRS})

add_executable(fetch_service fetch.cpp)

target_link_libraries(fetch_service ${PQXX_LIBRARIES})

Building the Project

Create required directories:
```
mkdir build
cd build
```
Run CMake to generate build files:
```
cmake ..
```
Build the project:
```
make
```
Run your application:
```
./fetch_service
```

Remember to replace placeholders for database name, user, and password with real values. The actual fetching of URLs and parsing their content is left as a placeholder, you can use libraries such as libcurl for fetching and gumbo-parser for parsing HTML content if you aim to expand the functionality further.

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Last updated 11 months ago