The very first thing to do before we can begin working with a
database, is actually connect to one. We do this by creating a
connection
object that will serve as our "handle"
on the connection:
connection Conn("dbname=test");
This gives us a connection object called Conn
.
The connection
constructor here takes one argument,
the "connect string." This string may be used to specify which host
on the network runs the database backend we wish to connect to, which
database we're interested in, which user name we'll be using to log
in, etc. Refer to the libpq connect
call for a
complete definition of what may go into the connect string. In this
case we're connecting to a database test
residing
on the local machine. By default the client will try to connect to a
server running on the local machine.
If no connection could be established, the connection
constructor may throw an exception immediately; or it may decide to
retry the connection later in case the problem is only temporary. In
the latter case, an exception may occur at some later point if the
problem turns out not to be so temporary after all.
The connection
can now act as a "service counter"
for our database; your client will use it to perform one or more
transactions related to the database.
Connections cannot be copied or assigned. Any attempt to do so will be met with a compiler error.
As a matter of design, libpqxx™ will not
allow you to perform queries on the connection
directly. You will need to open a transaction instead.
See the section on transactions below.