Library Version 18.1.40

Replacing Records Using Cursors
Prev | Chapter 4. Using Cursors | Next

## Replacing Records Using Cursors

You replace the data for a database record by using `Dbc::put()` with the `DB_CURRENT` flag.

    #include <db_cxx.h>
    #include <string.h>

    ...

    Db my_database(NULL, 0);
    Dbc *cursorp;

    int ret;
    char *key1str = "My first string";
    char *replacement_data = "replace me";

    try {
        // Database open omitted

        // Get the cursor
        my_database.cursor(NULL, &cursorp, 0);

        // Set up our DBTs
        Dbt key(key1str, strlen(key1str) + 1);
        Dbt data;

        // Position the cursor */
        ret = cursorp->get(&key, &data, DB_SET);
        if (ret == 0) {
            data.set_data(replacement_data);
            data.set_size(strlen(replacement_data) + 1);
            cursorp->put(&key, &data, DB_CURRENT);
        }
    } catch(DbException &e) {
            my_database.err(e.get_errno(), "Error!");
    } catch(std::exception &e) {
            my_database.errx("Error! %s", e.what());
    }

    // Cursors must be closed
    if (cursorp != NULL)
        cursorp->close();

    my_database.close(0);

Note that you cannot change a record's key using this method; the key parameter is always ignored when you replace a record.

When replacing the data portion of a record, if you are replacing a record that is a member of a sorted duplicates set, then the replacement will be successful only if the new record sorts identically to the old record. This means that if you are replacing a record that is a member of a sorted duplicates set, and if you are using the default lexicographic sort, then the replacement will fail due to violating the sort order. However, if you provide a custom sort routine that, for example, sorts based on just a few bytes out of the data item, then potentially you can perform a direct replacement and still not violate the restrictions described here.

Under these circumstances, if you want to replace the data contained by a duplicate record, and you are not using a custom sort routine, then delete the record and create a new record with the desired key and data.

Prev | Up | Next
Deleting Records Using Cursors | Home | Cursor Example