env3.cpp

Same as env2.c, but written in C++

#include <iostream>
#include <stdlib.h> /* for exit() */
#include <ham/hamsterdb.hpp>

#define MAX_DBS             3

#define DBNAME_CUSTOMER     1
#define DBNAME_ORDER        2
#define DBNAME_C2O          3   /* C2O: Customer To Order */

#define DBIDX_CUSTOMER      0
#define DBIDX_ORDER         1
#define DBIDX_C2O           2

#define MAX_CUSTOMERS       4
#define MAX_ORDERS          8

/* 
 * a structure for the "customer" database
 */
typedef struct
{
    int id;                 /* customer id - will be the key of the 
                               customer table */
    char name[32];          /* customer name */
    /* ... additional information could follow here */
} customer_t;

/* 
 * a structure for the "orders" database
 */
typedef struct
{
    int id;                 /* order id - will be the key of the 
                               order table */
    int customer_id;        /* customer id */
    char assignee[32];      /* assigned to whom? */
    /* ... additional information could follow here */
} order_t;

int 
run_demo(void)
{
    int i;
    ham::env env;           /* hamsterdb environment */
    ham::db db[MAX_DBS];    /* hamsterdb database objects */
    ham::cursor cursor[MAX_DBS]; /* a cursor for each database */
    ham::key key, cust_key, ord_key, c2o_key;
    ham::record record, cust_record, ord_record, c2o_record;

    customer_t customers[MAX_CUSTOMERS]={
        { 1, "Alan Antonov Corp." },
        { 2, "Barry Broke Inc." },
        { 3, "Carl Caesar Lat." },
        { 4, "Doris Dove Brd." }
    };

    order_t orders[MAX_ORDERS]={
        { 1, 1, "Joe" },
        { 2, 1, "Tom" },
        { 3, 3, "Joe" },
        { 4, 4, "Tom" },
        { 5, 3, "Ben" },
        { 6, 3, "Ben" },
        { 7, 4, "Chris" },
        { 8, 1, "Ben" }
    };

    /*
     * create a new database file for the environment
     */
    env.create("test.db");

    /*
     * then create the two databases in this environment; each database
     * has a name - the first is our "customer" database, the second 
     * is for the "orders"; the third manages our 1:n relation and
     * therefore needs to enable duplicate keys
     */
    db[DBIDX_CUSTOMER]=env.create_db(DBNAME_CUSTOMER);
    db[DBIDX_ORDER]   =env.create_db(DBNAME_ORDER);
    db[DBIDX_C2O]     =env.create_db(DBNAME_C2O, HAM_ENABLE_DUPLICATES);

    /* 
     * create a cursor for each database
     */
    for (i=0; i<MAX_DBS; i++) {
        cursor[i].create(&db[i]);
    }

    /*
     * insert the customers in the customer table
     *
     * INSERT INTO customers VALUES (1, "Alan Antonov Corp.");
     * INSERT INTO customers VALUES (2, "Barry Broke Inc.");
     * etc
     */
    for (i=0; i<MAX_CUSTOMERS; i++) {
        key.set_size(sizeof(int));
        key.set_data(&customers[i].id);

        record.set_size(sizeof(customer_t));
        record.set_data(&customers[i]);

        db[0].insert(&key, &record);
    }

    /*
     * and now the orders in the second database; contrary to env1, 
     * we only store the assignee, not the whole structure
     *
     * INSERT INTO orders VALUES (1, "Joe");
     * INSERT INTO orders VALUES (2, "Tom");
     */
    for (i=0; i<MAX_ORDERS; i++) {
        key.set_size(sizeof(int));
        key.set_data(&orders[i].id);

        record.set_size(sizeof(orders[i].assignee));
        record.set_data(orders[i].assignee);

        db[1].insert(&key, &record);
    }

    /*
     * and now the 1:n relationships; the flag HAM_DUPLICATE creates
     * a duplicate key, if the key already exists
     *
     * INSERT INTO c2o VALUES (1, 1);
     * INSERT INTO c2o VALUES (2, 1);
     * etc
     */
    for (i=0; i<MAX_ORDERS; i++) {
        key.set_size(sizeof(int));
        key.set_data(&orders[i].customer_id);

        record.set_size(sizeof(int));
        record.set_data(&orders[i].id);

        db[2].insert(&key, &record, HAM_DUPLICATE);
    }

    /*
     * now start the query - we want to dump each customer with his
     * orders
     *
     * loop over the customer; for each customer, loop over the 1:n table
     * and pick those orders with the customer id. then load the order
     * and print it
     *
     * the outer loop is similar to 
     * SELECT * FROM customers WHERE 1;
     */
    while (1) {
        customer_t *customer;

        try {
            cursor[0].move_next(&cust_key, &cust_record);
        }
        catch (ham::error &e) {
            /* reached end of the database? */
            if (e.get_errno()==HAM_KEY_NOT_FOUND)
                break;
            else {
                std::cerr << "cursor.move_next() failed: " << e.get_string()
                          << std::endl;
                return (-1);
            }
        }

        customer=(customer_t *)cust_record.get_data();

        /* print the customer id and name */
        std::cout << "customer " << customer->id << " ('" 
                  << customer->name << "')" << std::endl;

        /*
         * loop over the 1:n table
         *
         * before we start the loop, we move the cursor to the
         * first duplicate key
         *
         * SELECT * FROM customers, orders, c2o 
         *   WHERE c2o.customer_id=customers.id AND
         *      c2o.order_id=orders.id;
         */
        c2o_key.set_data(&customer->id);
        c2o_key.set_size(sizeof(int));

        try {
            cursor[2].find(&c2o_key);
        }
        catch (ham::error &e) {
            if (e.get_errno()==HAM_KEY_NOT_FOUND)
                continue;
            else {
                std::cerr << "cursor.find() failed: " << e.get_string()
                          << std::endl;
                return (-1);
            }
        }

        /* get the record of this database entry */
        cursor[2].move(0, &c2o_record);

        do {
            int order_id;

            order_id=*(int *)c2o_record.get_data();
            ord_key.set_data(&order_id);
            ord_key.set_size(sizeof(int));

            /* 
             * load the order 
             * SELECT * FROM orders WHERE id = order_id;
             */
            ord_record=db[1].find(&ord_key);

            std::cout << "  order: " << order_id << " (assigned to "
                      << (char *)ord_record.get_data() << ")" << std::endl;

            /*
             * the flag HAM_ONLY_DUPLICATES restricts the cursor
             * movement to the duplicate list.
             */
            try {
                cursor[2].move(&c2o_key, &c2o_record, 
                            HAM_CURSOR_NEXT|HAM_ONLY_DUPLICATES);
            }
            catch (ham::error &e) {
                /* reached end of the database? */
                if (e.get_errno()==HAM_KEY_NOT_FOUND)
                    break;
                else {
                    std::cerr << "cursor.move() failed: " << e.get_string()
                            << std::endl;
                    return (-1);
                }
            }

        } while(1);
    }

    /*
     * we're done! no need to cleanup, the destructors will prevent memory
     * leaks
     */

    std::cout << "success!" << std::endl;
    return (0);
}

int 
main(int argc, char **argv)
{
    try {
        return (run_demo());
    }
    catch (ham::error &e) {
        std::cerr << "run_demo() failed with unexpected error "
                  << e.get_errno() << " ('"
                  << e.get_string() << "')" << std::endl;
        return (-1);
    }
}