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Chapter 2. Databases
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## Chapter 2. Databases

In Berkeley DB, a database is a collection of records. Records, in turn, consist of key/data pairings.

Conceptually, you can think of a database as containing a two-column table where column 1 contains a key and column 2 contains data. Both the key and the data are managed using `Dbt` class instances (see Database Records for details on this class ). So, fundamentally, using a DB database involves putting, getting, and deleting database records, which in turns involves efficiently managing information encapsulated by `Dbt` objects. The next several chapters of this book are dedicated to those activities.

## Opening Databases

You open a database by instantiating a `Db` object and then calling its `open()` method.

Note that by default, DB does not create databases if they do not already exist. To override this behavior, specify the `DB_CREATE` flag on the `open()` method.

The following code fragment illustrates a database open:

    #include <db_cxx.h>

    ...

    Db db(NULL, 0);               // Instantiate the Db object

    u_int32_t oFlags = DB_CREATE; // Open flags;

    try {
        // Open the database
        db.open(NULL,                // Transaction pointer
                "my_db.db",          // Database file name
                NULL,                // Optional logical database name
                DB_BTREE,            // Database access method
                oFlags,              // Open flags
                0);                  // File mode (using defaults)
    // DbException is not subclassed from std::exception, so
    // need to catch both of these.
    } catch(DbException &e) {
        // Error handling code goes here
    } catch(std::exception &e) {
        // Error handling code goes here
    }

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