Problem/Motivation
Views supports a minimal set of aggregate functions that are hard coded into the default query plugin. It would be useful to have a way to add support for the full range of SQL aggregates available in MySQL & PostgreSQL (GROUP_CONCT/STRING_AGG, VARIANCE, ...), as well as providing a means of supporting the extended set of OGC spatial aggregates supported by PostgreSQL (ST_Union, ST_ClusterWithin, ...), and allowing any other user-defined aggregates that may be available.
Proposed resolution
Provide a plugin for defining new aggregates.
Use Annotation-based methods to expose plugin API, but maintain the current array format of aggregate type definition (see "Implementation Example" at bottom of issue for existing aggregate definition array format)..
Adding a new aggregate will be achieved by simply providing a properly formatted annotation and an empty sub-class of AggregatePluginBase(see Code 1).
The proposed implementation supports the existing aggregate definition array structure, and also how to provide backwards compatibility with a Drupal 7 approach
Code 1: Annotation block and empty class for VAR_POP plugin. This example will work inside a contrib module, if located in "modules/my_module_name/src/Plugin/views/aggregate/Var_Pop.php", or in Views core as "core/modules/views/src/Plugin/views/aggregate/Var_Pop.php".
<?php
namespace Drupal\views\Plugin\views\aggregate;
use Drupal\views\Plugin\views\PluginBase;
/**
* Aggregate plugin for SQL VAR_POP function.
*
* @ViewsAggregate(
* id = "var_pop",
* function = "var_pop",
* title = @Translation("Variance (pop)"),
* method = "aggregationMethodSimple",
* handler = {
* "argument" = "groupby_numeric",
* "field" = "numeric",
* "filter" = "groupby_numeric",
* "sort" = "groupby_numeric"
* },
* help = @Translation("Population Variance."),
* )
*/
class Var_Pop extends AggregatePluginBase {
// Class methods…
}
For further details, see "Implementation Example", and for further details a related issue with patch for implementation in D7 "
Support Plugins for Views Aggregate in D7 →
").
Remaining tasks
- Test
User interface changes
None.
API changes
Add Annotation-based plugin support for ViewsAggregate
Data model changes
None.
Implementation Example
Code 2: Plugin definition array excerpt.
return array(
...
'count' => array(
'title' => $this->t('Count'),
'method' => 'aggregationMethodSimple',
'handler' => array(
'argument' => 'groupby_numeric',
'field' => 'numeric',
'filter' => 'groupby_numeric',
'sort' => 'groupby_numeric',
),
),
Code 3: Sample implementation of VAR_SAMP in Drupal 7 using Ctools plugin.
function views_views_plugins() {
return array(
'query_aggregate' => array(
'var_samp' => array(
'title' => t('Sample Variance'),
'method' => 'views_query_default_aggregation_method_simple',
'handler' => array(
'argument' => 'views_handler_argument_group_by_numeric',
'filter' => 'views_handler_filter_group_by_numeric',
'sort' => 'views_handler_sort_group_by_numeric',
),
),
...
