Writing MySQL-Based Programs - MySQL - page 34

The require statement tells Ruby to load the DBI module. It's unnecessary to load the
MySQL driver module explicitly. DBI does that itself when the script connects to the
database server.
To establish the connection, pass a data source name (DSN) and the MySQL username
and password to the connect() method. The DSN is required. The other arguments are
optional, although usually it's necessary to supply a username and password.
The DSN specifies which database driver to use and other options that indicate where
to connect. For MySQL programs, the DSN typically has one of these formats:
DBI : Mysql : db_name : host_name
DBI : Mysql : name = value ; name = value . . .
As with Perl DBI, the second colon in the DSN is required even if you specify no fol‐
lowing options.
Use the DSN components as follows:
• The first component is always DBI or dbi .
• The second component tells DBI which database driver to use. For MySQL, the
name is Mysql .
• The third component, if present, is either a database name and hostname separated
by a colon, or a semicolon-separated list of name = value pairs that specify additional
connection options, in any order. For our purposes, the two most relevant options
are host and database , to specify the hostname where the MySQL server is running
and the default database.
Based on that information, the DSN for connecting to the cookbook database on the
local host localhost looks like this:
DBI : Mysql : host = localhost ; database = cookbook
If you omit the host option, its default value is localhost . These two DSNs are equiv‐
alent:
DBI : Mysql : host = localhost ; database = cookbook
DBI : Mysql : database = cookbook
To select no default database, omit the database option.
Assuming that connect() succeeds, it returns a database handle that contains infor‐
mation about the state of the connection. Ruby DBI scripts in this topic conventionally
use dbh to signify a database handle.
If the connect() method fails, DBI raises an exception. To handle exceptions, put the
statements that might fail inside a begin block, and use a rescue clause that contains
the error-handling code. Exceptions that occur at the top level of a script (that is, outside