Type:string (table name)

Means that the relation to the records of foreign_table is done with a M-M relation with a third “intermediate” table.

That table typically has three columns:

uid_local, uid_foreign
Storing uids of both sides. If done right, this is reflected in the table name - tx_foo_local_foreign_mm
is a required field used for ordering the items.
further fields
May exist, in particular if MM_match_fields is involved in the set up.

The field which is configured as “inline” is not used for data-storage any more but rather it’s set to the number of records in the relation on each update, so the field should be an integer.


Copying with MM relations will not create a copy of the value. Thus copying the record Org with Org->orgA and Org->orgB as New results in New->orgA and New->orgB instead of New->newA and New->newB. Deleting the relation New->orgA will result in a broken relation Org->orgA.


If the “multiple” feature is used with MM relations you MUST set this value to true and include a UID field! Otherwise sorting and removing relations will be buggy.

Type:string (field name)

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

For example if the field “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 persons.employers, you would need to set the MM_opposite_field value of the TCA configuration of the persons.employers field to the string “employees”.


Bidirectional references only get registered once on the native side in sys_refindex.