..  include:: /Includes.rst.txt

..  _columns-none:
..  _columns-none-introduction:

================
The `none` field
================

..  include:: /Images/Rst/None1.rst.txt

There are three columns config types that do similar things but still have subtle differences between them.
These are the :ref:`none type <columns-none>`, the :ref:`passthrough type <columns-passthrough>` and the
:ref:`user type <columns-user>`.

Characteristics of `none`:

*   The :ref:`DataHandler <t3coreapi:datahandler-basics>` discards values send for type `none` and never
    persists or updates them in the database.
*   Type `none` is the only type that does **not** necessarily need a database field.
*   Type `none` fields does have a default `renderType` in FormEngine that displays the value as readonly
    if a database field exists and the value can be formatted.
*   If no database field exists for `none` fields, an empty readonly input field is rendered by default.
*   Type `none` fields are designed to be not rendered at other places in the backend, for instance they can
    not be selected to be displayed in the list module "single table view" if everything has been configured
    correctly.

The `none` field can be useful, if:

*   A "virtual" field that has no database representation is needed. A simple example could be a rendered
    map that receives values from `latitude` and `longitude` fields but that needs to database representation
    itself.
*   A third party feeds the database field with a value and the value should be formatted and displayed
    in FormEngine. However, a :ref:`input type <columns-input>` with :php:`readOnly=true` is usually better
    suited to do that.

Since the formatting part of `none` fields can be done with `input` type as well, most useful usage
of type `none` fields is a "virtual" field that is combined with a custom
:ref:`renderType <t3coreapi:FormEngine-Rendering-NodeExpansion>` by an extension.
The TYPO3 core makes little or no use of `none` fields itself.


..  toctree::
    :titlesonly:

    Examples
    Properties/Index