..  include:: /Includes.rst.txt
..  _columns-select-properties-mm:

==
MM
==

..  versionadded:: 11.4
    TCA table column fields that define :php:`['config']['MM']` can omit the
    specification of the intermediate MM table layout in
    :ref:`ext_tables.sql <t3coreapi:ext_tables-sql>`. The TYPO3 database
    analyzer takes care of proper schema definition.

    Extensions are strongly encouraged to drop :sql:`CREATE TABLE` definitions
    from the :file:`ext_tables.sql` file for those intermediate tables
    referenced by TCA table columns. Dropping these definitions allows the Core
    to adapt and migrate definitions if needed.

..  confval:: MM
    :name: select-mm
    :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']
    :type: string (table name)
    :Scope: Proc.

    This value contains the name of the table in which to store a MM relation.
    It is used together with
    :ref:`foreign_table <columns-select-properties-foreign-table>`.

    The database field with a MM property only stores the number of records
    in the relation.

    Please have a look into the additional information
    in the :ref:`MM common property description <tca_property_MM>`.


Examples
========

..  _tca_example_select_single_15:

Select field with foreign table via MM table
--------------------------------------------

..  include:: /Images/Rst/SelectSingle15.rst.txt

..  include:: /CodeSnippets/SelectSingle15.rst.txt


Related configurations
======================

..  confval:: MM_hasUidField (type => select)

    :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']
    :type: boolean
    :Scope: Proc.

    If the :ref:`multiple <tca_property_multiple>` property is set with MM
    relations you **must** set this value to :php:`true` and include a UID field.
    Otherwise, sorting and removing relations will be buggy.


..  confval:: MM_insert_fields (type => select)

    ..  deprecated:: 12.4
        As there is no API to retrieve these values again, having a static value
        in an additional column is useless. Therefore, this setting is removed
        in TYPO3 v13. :ref:`More details <ext_core:deprecation-100335-1679998903>`

    :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']
    :type: array
    :Scope: Proc.

    Array of field => value pairs to insert when writing new MM relations.

..  _columns-select-properties-mm-match-fields:
..  confval:: MM_match_fields
    :name: select-mm-match-fields
    :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']
    :type: array
    :Scope: Display / Proc.

    Array of field => value pairs to both insert and match against when
    writing/reading MM relations.


..  confval:: MM_opposite_field
    :name: select-mm-opposite-field
    :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']
    :type: string (field name)
    :Scope: Proc.

    If you want to make a MM relation editable from the foreign side
    (bidirectional) of the relation as well, you need to set
    :php:`MM_opposite_field` on the foreign side to the field name on
    the local side.

    For example, if the field :sql:`companies.employees` is your local side and
    you want to make the same relation editable from the foreign side of the
    relation in a field called :sql:`persons.employers`, you would need to set
    the :php:`MM_opposite_field` value of the TCA configuration of the
    :sql:`persons.employers` field to the string "employees".

    ..  note::
        Bidirectional references only get registered once on the native side in
        :sql:`sys_refindex`.


..  confval:: MM_oppositeUsage
    :name: select-mm-oppositeUsage
    :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']
    :type: array
    :Scope: Proc.

    In a MM bidirectional relation using
    :ref:`group match fields <columns-group-properties-mm-match-fields>`
    the opposite side needs to know about the match fields for certain operations
    (for example, when a copy is created in a
    :doc:`workspace <ext_workspaces:Index>`) so that relations are carried over
    with the correct information.

    :php:`MM_oppositeUsage` is an array which references which fields contain
    the references to the opposite side, so that they can be queried for match
    field configuration.


..  confval:: MM_table_where
    :name: select-mm-table-where
    :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']
    :type: string (SQL WHERE)
    :Scope: Proc.

    Additional where clause used when reading MM relations.

    Example:

    ..  code-block:: text

        {#uid_local} = ###THIS_UID###

    The above example uses the special field quoting syntax :php:`{#...}`
    around identifiers to be as :ref:`DBAL <t3coreapi:database>`-compatible as
    possible.