Multi-Select [tags]

The “Multi-select [tags]” attribute creates an m:n relation to another table — either a MetaModels table or any Contao table (e.g. tl_member, tl_page). The link is stored in a dedicated relation table (tl_metamodel_tag_relation), so no own column is created in the MetaModel table for this attribute. Typical use cases:

• Assigning multiple tags to a product

• Linking an article with multiple categories or authors

• Selecting multiple regions, languages, or target audiences

The selection in the backend can be displayed as a checkbox list, checkbox wizard, tree picker, or searchable dropdown.

Note

For relations between two multilingual MetaModels, the monolingual variant “Multi-select” should be used — MetaModels automatically recognizes the language and switches accordingly.

See also

For special cases with their own language column in the referenced table, Translated Multi-Select [tags] is available.

Installation

The attribute is installed via the Contao Manager or Composer:

composer require metamodels/attribute_tags

Settings when Creating the Attribute

In addition to the general attribute settings (name, column name, description, override variants), the attribute offers the following specific options:

Option	Description
Database table	The table from which the selection values are obtained. MetaModels tables as well as all Contao database tables are available.
Table column for label/name	The column of the source table whose content is displayed as the label in the selection list.
Multi-select ID	The column that serves as the unique identifier (stored value). Default: id.
Multi-select alias	The column used as a readable identifier in filter widgets.
Multi-select sorting	Column by which the selection list is sorted.
Sort direction	Ascending (A → Z) or descending (Z → A).
SQL (WHERE condition)	Optional SQL WHERE condition to restrict the selection list. The alias t represents the source table (e.g. t.published = '1'). The condition does not filter when the widget type “Popup picker” is selected.
Filter	Selection of a MetaModels filter set for dynamic restriction of options.
Filter parameters	Default values for the parameters of the selected filter set.

Settings in Render Settings

The multi-select attribute has no specific render settings. In the attribute list of a render setting, the usual options are available:

Option	Description
Template	Selection of a custom template for the output of the linked values.
CSS class	Optional CSS class added to the output element.

Settings in the Input Form

When the attribute is added to an input form, the following options are available:

Display

Option	Description
Backend class	CSS classes for the display of the field in the backend form.
Template for backend	Selection of a custom widget template for the backend form.
Template for frontend	Selection of a custom widget template for frontend editing (only available if the “Frontend Editing” extension is installed).
Select display type	Display type of the multiple selection: Checkbox menu — Classic checkbox list Checkbox wizard — Checkbox list with up/down sorting Popup picker — Selection via a tree picker (for hierarchical source tables such as tl_page or tl_files) Tag list — Searchable dropdown with chosen.js
Lowest level (tree)	For tree picker: records below this level are not selectable (0 = no restriction).
Highest level (tree)	For tree picker: records above this level are not selectable (0 = no restriction).

Functions

Option	Description
Required field	Makes the field a required field.

Overview (backend filter and search)

Option	Description
Filterable	The attribute is available in the backend as a filter criterion.
Searchable	The attribute is available in the backend as a search field.

Filter Rules

The multi-select attribute can be used with the following filter rules:

Filter rule	Note
Multi-select	Filters by one or more selected values from the source table; e.g. all products with a specific tag.
Filter on attribute of model with a relation	Filters MetaModel items based on an attribute value of the linked MetaModel; e.g. all products whose tags have a specific characteristic.

Special Functions

Database storage

The relations are not stored in the MetaModel table, but in the dedicated junction table tl_metamodel_tag_relation with the columns att_id (attribute ID), item_id (item ID), value_id (ID of the linked record), and value_sorting (sort order). This eliminates a column in the MM table and no database migration is needed.

SQL WHERE condition

In the WHERE condition, the alias t represents the source table. Example for filtering on published entries:

t.published = '1'