ex_extractor.c

Shows how to extend WiredTiger with a more complex custom extractor.

/*-
 * Public Domain 2008-2014 WiredTiger, Inc.
 *
 * This is free and unencumbered software released into the public domain.
 *
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 *
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * ex_extractor.c
 *      Example of how to use a WiredTiger custom index extractor extension.
 */

#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <wiredtiger.h>

int add_extractor(WT_CONNECTION *conn);

static const char *home;

struct president_data {
        int             id;
        const char      *last_name;
        const char      *first_name;
        uint16_t        term_start;
        uint16_t        term_end;
};

static const struct president_data example_data[] = {
        { 0, "Obama", "Barack", 2009, 2014 },
        { 1, "Bush", "George W", 2001, 2009 },
        { 2, "Clinton", "Bill", 1993, 2001 },
        { 3, "Bush", "George H", 1989, 1993 },
        { 4, "Reagan", "Ronald", 1981, 1989 },
        { 0, NULL, NULL, 0, 0 }
};
/*
 * Number of years this data spans
 */
#define YEAR_BASE       1981
#define YEAR_SPAN       (2014-1981)

/*
 * A custom index extractor function that adds an index entry for each year of
 * the given president's term.
 */
static int
my_extract(WT_EXTRACTOR *extractor, WT_SESSION *session,
    const WT_ITEM *key, const WT_ITEM *value, WT_CURSOR *result_cursor)
{
        char *last_name, *first_name;
        uint16_t term_end, term_start, year;
        int ret;

        /* Unused parameters */
        (void)extractor;
        (void)key;

        /* Unpack the value. */
        if ((ret = wiredtiger_struct_unpack(
            session, value->data, value->size, "SSHH",
            &last_name, &first_name, &term_start, &term_end)) != 0)
                return (ret);

        /*
         * We have overlapping years, so multiple records may share the same
         * index key.
         */
        for (year = term_start; year <= term_end; ++year) {
                /*
                 * Note that the extract callback is called for all operations
                 * that update the table, not just inserts.  The user sets the
                 * key and uses the cursor->insert() method to return the index
                 * key(s).  WiredTiger will perform the required operation
                 * (such as a remove()).
                 */
                fprintf(stderr, "EXTRACTOR: index op for year %d: %s %s\n",
                    year, first_name, last_name);
                result_cursor->set_key(result_cursor, year);
                if ((ret = result_cursor->insert(result_cursor)) != 0) {
                        fprintf(stderr, "EXTRACTOR: op year %d: error %d\n",
                            year, ret);
                        return (ret);
                }
        }
        return (0);
}

/*
 * The terminate method is called to release any allocated resources when the
 * table is closed.  In this example, no cleanup is required.
 */
static int
my_extract_terminate(WT_EXTRACTOR *extractor, WT_SESSION *session)
{
        (void)extractor;
        (void)session;

        return (0);
}

int
add_extractor(WT_CONNECTION *conn)
{
        int ret;

        static WT_EXTRACTOR my_extractor = {
            my_extract, NULL, my_extract_terminate
        };
        ret = conn->add_extractor(conn, "my_extractor", &my_extractor, NULL);

        return (ret);
}

/*
 * Read the index by year and print out who was in office that year.
 */
static int
read_index(WT_SESSION *session)
{
        WT_CURSOR *cursor;
        int i, ret;
        char *first_name, *last_name;
        uint16_t term_end, term_start, year;

        srandom((unsigned int)getpid());
        ret = session->open_cursor(
            session, "index:presidents:term", NULL, NULL, &cursor);
        /*
         * Pick 10 random years and read the data.
         */
        for (i = 0; i < 10; i++) {
                year = (uint16_t)((random() % YEAR_SPAN) + YEAR_BASE);
                cursor->set_key(cursor, year);
                if ((ret = cursor->search(cursor)) == 0) {
                        if ((ret = cursor->get_value(cursor, &last_name,
                            &first_name, &term_start, &term_end)) != 0)
                                break;
                        printf("Year %d: %s %s\n", year, first_name, last_name);
                        continue;
                }

                fprintf(stderr, "Error %d for year %d\n", ret, year);
                break;
        }
        ret = cursor->close(cursor);
        return (ret);
}

/*
 * Remove some items from the primary table.
 */
static int
remove_items(WT_SESSION *session)
{
        WT_CURSOR *cursor;
        struct president_data p;
        int i, ret;

        /*
         * Removing items from the primary table will call the extractor
         * for the index and allow our custom extractor code to handle
         * each custom key.
         */
        ret = session->open_cursor(
            session, "table:presidents", NULL, NULL, &cursor);
        /*
         * Just remove the first few items.
         */
        for (i = 0; example_data[i].last_name != NULL && i < 2; i++) {
                p = example_data[i];
                cursor->set_key(cursor, p.id);
                ret = cursor->remove(cursor);
        }
        return (ret);
}

/*
 * Set up the table and index of the data.
 */
static int
setup_table(WT_SESSION *session)
{
        WT_CURSOR *cursor;
        struct president_data p;
        int i, ret;

        /* Create the primary table. It has a key of the unique ID. */
        ret = session->create(session, "table:presidents",
            "key_format=I,value_format=SSHH,"
            "columns=(ID,last_name,first_name,term_begin,term_end)");

        /*
         * Create the index that is generated with an extractor. The index
         * will generate an entry in the index for each year a president
         * was in office.
         */
        ret = session->create(session, "index:presidents:term",
            "key_format=H,columns=(term),extractor=my_extractor");

        ret = session->open_cursor(
            session, "table:presidents", NULL, NULL, &cursor);
        for (i = 0; example_data[i].last_name != NULL; i++) {
                p = example_data[i];
                cursor->set_key(cursor, p.id);
                cursor->set_value(cursor,
                    p.last_name, p.first_name, p.term_start, p.term_end);
                fprintf(stderr, "SETUP: table insert %d-%d: %s %s\n",
                    p.term_start, p.term_end,
                    p.first_name, p.last_name);
                ret = cursor->insert(cursor);
        }
        return (ret);
}

int
main(void)
{
        WT_CONNECTION *conn;
        WT_SESSION *session;
        int ret;

        /*
         * Create a clean test directory for this run of the test program if the
         * environment variable isn't already set (as is done by make check).
         */
        if (getenv("WIREDTIGER_HOME") == NULL) {
                home = "WT_HOME";
                ret = system("rm -rf WT_HOME && mkdir WT_HOME");
        } else
                home = NULL;

        ret = wiredtiger_open(home, NULL, "create,cache_size=500M", &conn);
        ret = add_extractor(conn);
        ret = conn->open_session(conn, NULL, NULL, &session);

        ret = setup_table(session);
        ret = read_index(session);
        ret = remove_items(session);

        ret = conn->close(conn, NULL);

        return (ret);
}