Class DbConnection

src/main/java/com/shop/database/DbConnection.java:35–1591

public class DbConnection {
    private Connection con;
    private static DbConnection dbc;

    public void createTablesIfNotExists() {
        String createUsersTable = "CREATE TABLE IF NOT EXISTS users (" +
                "username TEXT PRIMARY KEY NOT NULL, " +
                "email TEXT NOT NULL, " +
                "first_name TEXT NOT NULL, " +
                "last_name TEXT NOT NULL, " +
                "password TEXT NOT NULL, " +
                "role VARCHAR(25) NOT NULL DEFAULT 'user', " +
                "created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP" +
                ");";

        String createProcessorsTable = "CREATE TABLE IF NOT EXISTS processors (" +
                "id SERIAL PRIMARY KEY, " +
                "name TEXT NOT NULL, " +
                "brand TEXT NOT NULL, " +
                "cores INT NOT NULL, " +
                "threads INT NOT NULL, " +
                "base_clock DECIMAL(5,2) NOT NULL, " +
                "boost_clock DECIMAL(5,2) NOT NULL, " +
                "link TEXT NOT NULL" +
                ");";

        String createGraphicsCardsTable = "CREATE TABLE IF NOT EXISTS graphic_cards (" +
                "id SERIAL PRIMARY KEY, " +
                "name TEXT NOT NULL, " +
                "brand TEXT NOT NULL, " +
                "memory_size INT NOT NULL, " +
                "memory_type TEXT NOT NULL, " +
                "link TEXT NOT NULL" +
                ");";

        String createPowerSuppliesTable = "CREATE TABLE IF NOT EXISTS power_supplies (" +
                "id SERIAL PRIMARY KEY, " +
                "name TEXT NOT NULL, " +
                "brand TEXT NOT NULL, " +
                "wattage INT NOT NULL, " +
                "efficiency_rating TEXT NOT NULL, " +
                "link TEXT NOT NULL" +
                ");";

        String createMotherboardsTable = "CREATE TABLE IF NOT EXISTS motherboards (" +
                "id SERIAL PRIMARY KEY, " +
                "name TEXT NOT NULL, " +
                "brand TEXT NOT NULL, " +
                "socket_type TEXT NOT NULL, " +
                "form_factor TEXT NOT NULL, " +
                "max_memory INT NOT NULL, " +
                "link TEXT NOT NULL" +
                ");";

        String createCoolersTable =  "CREATE TABLE IF NOT EXISTS coolers (" + 
                "id SERIAL PRIMARY KEY, "+ 
                "name TEXT NOT NULL," + 
                "brand TEXT NOT NULL," +