Section: Tcl Database Connectivity (n)
Updated: 8.6
Page Index



tdbc::odbc - TDBC-ODBC bridge  


package require tdbc::odbc 1.0

tdbc::odbc::connection create db connectionString ?-option value...?
tdbc::odbc::connection new connectionString ?-option value...?

tdbc::odbc::datasources ?-system|-user?


tdbc::odbc::datasource command driverName ?keyword-value?...



The tdbc::odbc driver provides a database interface that conforms to Tcl DataBase Connectivity (TDBC) and allows a Tcl script to connect to any SQL database presenting an ODBC interface. It is also provided as a worked example of how to write a database driver in C, so that driver authors have a starting point for further development.

Connection to an ODBC database is established by invoking tdbc::odbc::connection create, passing it the name to be used as a connection handle, followed by a standard ODBC connection string. As an alternative, tdbc::odbc::connection new may be used to create a database connection with an automatically assigned name. The return value from tdbc::odbc::connection new is the name that was chosen for the connection handle.

The connection string will include at least a DRIVER or DSN keyword, and may include others that are defined by a particular ODBC driver. (If the local ODBC system supports a graphical user interface, the -parent option (see below) may allow calling tdbc::odbc::connection create with an empty connection string.)

The side effect of tdbc::odbc::connection create is to create a new database connection.. See tdbc::connection(n) for the details of how to use the connection to manipulate a database.

In addition to a standard TDBC interface, tdbc::odbc supports three additional ccommands. The first of these, tdbc::odbc::datasources, which returns a Tcl list enumerating the named data sources available to the program (for connection with the DSN keyword in the connection string). The result of tdbc::odbc::datasources may be constrained to only system data sources or only user data sources by including the -system or -user options, respectively.

The tdbc::odbc::drivers command returns a dictionary whose keys are the names of drivers available for the DRIVER keyword in the connection string, and whose values are descriptions of the drivers.

The tdbc::odbc::datasource command allows configuration of named data sources on those systems that support the ODBC Installer application programming interface. It accepts a command, which specifies the operation to be performed, the name of a driver for the database in question, and a set of keyword-value pairs that are interpreted by the given driver. The command must be one of the following:

Adds a user data source. The keyword-value pairs must include at least a DSN option naming the data source
Adds a system data source. The keyword-value pairs must include at least a DSN option naming the data source
Configures a user data source. The keyword-value pairs will usually include a DSN option naming the data source. Some drivers will support other options, such as the CREATE_DB option to the Microsoft Access driver on Windows.
Configures a system data source.
Removes a user data source. The keyword-value pairs must include a DSN option specifying the data source to remove.
Removes a system data source. The keyword-value pairs must include a DSN option specifying the data source to remove.


The tdbc::odbc::connection create object command supports the -encoding, -isolation, -readonly and -timeout options common to all TDBC drivers. The -encoding option will succeed only if the requested encoding is the same as the system encoding; tdbc::odbc does not attempt to specify alternative encodings to an ODBC driver. (Some drivers accept encoding specifications in the connection string.)

In addition, if Tk is present in the requesting interpreter, and the local system's ODBC driver manager supports a graphical user interface, the tdbc::odbc::connection create object command supports a -parent option, whose value is the path name of a Tk window. If this option is specified, and a connection string does not specify all the information needed to connect to an interface, the ODBC driver manager will display a dialog box to request whatever additional information is required. The requesting interpreter will block until the user dismisses the dialog, at which point the connection is made.  


Sincs ODBC connection strings are driver specific, it is often difficult to find the documentation needed to compose them. The following examples are known to work on most Windows systems and provide at least a few useful things that a program can do.

tdbc::odbc::connection create db \

Connects to a named data source "PAYROLL", providing "aladdin" as a user name and "Sesame" as a password. Uses db as the name of the connection.

set connString {DRIVER={Microsoft Access Driver (*.mdb)};}
append connString {FIL={MS Access}\;}
append connString {DBQ=} \
    [file nativename [file normalize $fileName]]
tdbc::odbc::connection create db2 -readonly 1 $connString

Opens a connection to a Microsoft Access database file whose name is in $fileName. The database is opened in read-only mode. The resulting connection is called "db2".

tdbc::odbc::connection create db3 \

Opens a connection to a SQLite3 database whose name is in "$fileName".

tdbc::odbc::datasource add \
    {Microsoft Access Driver (*.mdb)} \
    DSN=MyTestDatabase \
    DBQ=[file native [file normalize $fileName]]

Creates a new user data source with the name, "MyTestDatabase" bound to a Microsoft Access file whose path name is in "$fileName". No connection is made to the data source until the program calls tdbc::odbc::connection create.

tdbc::odbc::datasource configure \
    {Microsoft Access Driver (*.mdb)} \
    CREATE_DB=[file native [file normalize $fileName]] \

Creates a new, empty Microsoft Access database in the file identified by "$fileName". No connection is made to the database until the program calls tdbc::odbc::connection create.  


tdbc(n), tdbc::connection(n), tdbc::resultset(n), tdbc::statement(n)  


TDBC, SQL, ODBC, database, connectivity, connection  


Copyright (c) 2008 by Kevin B. Kenny.



LinuxReviews : manual page archive : mann