Mk4tcl is an extension that allows operations on Metakit databases from Tcl scripts. The homepage, containing full documentation, is located at http://www.equi4.com/metakit/tcl.html. We do not intend to duplicate it, we will just review the most important Tcl commands introduced by this extension.

If you are using the prepared Tcl distribution, there is a good chance that the extension is already a part of it. Otherwise, you will have to download the extension from its homepage and install it. To start using the extension, you have to load it in your script using:

package require Mk4tcl

To operate on data files, use the mk::file command with the appropriate arguments. Mk4tcl introduces the concept of a tag—that is, an identifier for an opened data file.

To create or open an existing Metakit file, use mk::file open, for example:

mk::file open myTag myDatabase.mk

Here the tag is named myTag and the data file myDatabase.mk. Note that unless you use the option nocommit, all pending changes will be saved to file when it is closed.

Other uses of mk::file include:

To specify a view or a row with in a view, you can use a path. The way to construct a path can be easily described using the following examples:

To operate on a view, use the mk::view command. In the following commands, myTag.myView is an example of the path denoting the view, and it will sometimes be referred to by using path to make the syntax more readable:

Once you have opened the data file and defined the view, it is time to operate on the data. You can start operating on rows with the mk::row command:

To get values from the row, use the mk::get path command. It returns a list of column names and values.

To set values in an already existing row, you can use the mk::set path command like this:

mk::set path name "George S." birthYear 1978

The path must denote the row number (in the myTag.myView!R format). If that row does not exist, it will be created. If you use a value higher than the index of the last row, the gap will be filled in with rows of empty values.

Knowing all this, lets consider the following example code:

package require Mk4tcl
proc printRows {path rows} {
foreach i $rows {
puts [mk::get $path!$i]
}
}
mk::file open myTag myDatabase.mk
mk::view layout myTag.people {name birthYear:I}
mk::row append myTag.people name "George S." birthYear 1978
mk::row append myTag.people name "John Gray" birthYear 1973 sex male
mk::row append myTag.people name "Jeniffer Snake" birthYear 1982 sex female
mk::row append myTag.people name "Judith Brow" birthYear 1987 sex female
mk::set myTag.people!9 name "Johnny B." birthYear 1977 sex male

This set of instructions will create a database stored in the myDatabase.mk file and put inside it a total of 10 rows.

For easy selection of rows, use the mk::select path ?options? command. The command returns a list of row numbers that matched the selection criteria, which was specified in the options arguments. By default, the command will select all rows:

set rows [mk::select myTag.people]
printRows myTag.people $rows

The previous command will result in the following output:

name {George S.} birthYear 1978 sex {}

name {John Gray} birthYear 1973 sex male

name {Jeniffer Snake} birthYear 1982 sex female

name {Judith Brow} birthYear 1987 sex female

name {} birthYear 0 sex {}

name {} birthYear 0 sex {}

name {} birthYear 0 sex {}

name {} birthYear 0 sex {}

name {} birthYear 0 sex {}

name {Johnny B.} birthYear 1977 sex male

There is no point in doubling the documentation and describing all options of mk::select. Instead, we will show an example of the usage of some of them: