.. _transformations:

Transformations
===============

.. note::

    You need to have configured the :ref:`linked-tables` for using transformations
    feature.

.. _transformationsintro:

Introduction
++++++++++++

To enable transformations, you have to setup the ``column_info``
table and the proper directives. Please see the :ref:`config` on how to do so.

You can apply different transformations to the contents of each
column. The transformation will take the content of each column and
transform it with certain rules defined in the selected
transformation.

Say you have a column 'filename' which contains a filename. Normally
you would see in phpMyAdmin only this filename. Using transformations
you can transform that filename into a HTML link, so you can click
inside of the phpMyAdmin structure on the column's link and will see
the file displayed in a new browser window. Using transformation
options you can also specify strings to append/prepend to a string or
the format you want the output stored in.

For a general overview of all available transformations and their
options, you can consult your *<www.your-host.com>/<your-install-
dir>/transformation\_overview.php* installation.

For a tutorial on how to effectively use transformations, see our
`Link section <https://www.phpmyadmin.net/docs/>`_ on the
official phpMyAdmin homepage.

.. _transformationshowto:

Usage
+++++

Go to your *tbl\_structure.php* page (i.e. reached through clicking on
the 'Structure' link for a table). There click on "Change" (or change
icon) and there you will see three new fields at the end of the line.
They are called ':term:`Media type`', 'Browser transformation' and
'Transformation options'.

* The field ':term:`Media type`' is a drop-down field. Select the :term:`Media type` that
  corresponds to the column's contents. Please note that transformations
  are inactive as long as no :term:`Media type` is selected.
* The field 'Browser transformation' is a drop-down field. You can
  choose from a hopefully growing amount of pre-defined transformations.
  See below for information on how to build your own transformation.
  There are global transformations and mimetype-bound transformations.
  Global transformations can be used for any mimetype. They will take
  the mimetype, if necessary, into regard. Mimetype-bound
  transformations usually only operate on a certain mimetype. There are
  transformations which operate on the main mimetype (like 'image'),
  which will most likely take the subtype into regard, and those who
  only operate on a specific subtype (like 'image/jpeg'). You can use
  transformations on mimetypes for which the function was not defined
  for. There is no security check for you selected the right
  transformation, so take care of what the output will be like.
* The field 'Transformation options' is a free-type textfield. You have
  to enter transform-function specific options here. Usually the
  transforms can operate with default options, but it is generally a
  good idea to look up the overview to see which options are necessary.
  Much like the ENUM/SET-Fields, you have to split up several options
  using the format 'a','b','c',...(NOTE THE MISSING BLANKS). This is
  because internally the options will be parsed as an array, leaving the
  first value the first element in the array, and so forth. If you want
  to specify a MIME character set you can define it in the
  transformation\_options. You have to put that outside of the pre-
  defined options of the specific mime-transform, as the last value of
  the set. Use the format "'; charset=XXX'". If you use a transform, for
  which you can specify 2 options and you want to append a character
  set, enter "'first parameter','second parameter','charset=us-ascii'".
  You can, however use the defaults for the parameters: "'','','charset
  =us-ascii'". The default options can be configured using
  :config:option:`$cfg['DefaultTransformations']`

.. _transformationsfiles:

File structure
++++++++++++++

All specific transformations for mimetypes are defined through class
files in the directory 'libraries/classes/Plugins/Transformations/'. Each of
them extends a certain transformation abstract class declared in
libraries/classes/Plugins/Transformations/Abs.

They are stored in files to ease up customization and easy adding of
new transformations.

Because the user cannot enter own mimetypes, it is kept sure that
transformations always work. It makes no sense to apply a
transformation to a mimetype the transform-function doesn't know to
handle.

There is a file called ':file:`libraries/classes/Plugins/Transformations.php`' that provides some
basic functions which can be included by any other transform function.

The file name convention is ``[Mimetype]_[Subtype]_[Transformation
Name].php``, while the abstract class that it extends has the
name ``[Transformation Name]TransformationsPlugin``. All of the
methods that have to be implemented by a transformations plug-in are:

#. getMIMEType() and getMIMESubtype() in the main class;
#. getName(), getInfo() and applyTransformation() in the abstract class
   it extends.

The getMIMEType(), getMIMESubtype() and getName() methods return the
name of the MIME type, MIME Subtype and transformation accordingly.
getInfo() returns the transformation's description and possible
options it may receive and applyTransformation() is the method that
does the actual work of the transformation plug-in.

Please see the :file:`libraries/classes/Plugins/Transformations/TEMPLATE` and
:file:`libraries/classes/Plugins/Transformations/TEMPLATE\_ABSTRACT` files for adding
your own transformation plug-in. You can also generate a new
transformation plug-in (with or without the abstract transformation
class), by using
:file:`scripts/transformations_generator_plugin.sh` or
:file:`scripts/transformations_generator_main_class.sh`.

The applyTransformation() method always gets passed three variables:

#. **$buffer** - Contains the text inside of the column. This is the
   text, you want to transform.
#. **$options** - Contains any user-passed options to a transform
   function as an array.
#. **$meta** - Contains an object with information about your column. The
   data is drawn from the output of the `mysql\_fetch\_field()
   <https://www.php.net/mysql_fetch_field>`_ function. This means, all
   object properties described on the `manual page
   <https://www.php.net/mysql_fetch_field>`_ are available in this
   variable and can be used to transform a column accordingly to
   unsigned/zerofill/not\_null/... properties. The $meta->mimetype
   variable contains the original :term:`Media type` of the column (i.e.
   'text/plain', 'image/jpeg' etc.)
