Stop doing 1+N queries when using summary fields with relations (e.g. GridFieldDataColumns or GridFieldExportButton)

beMoreEfficient.php

<?php

use SilverStripe\ORM\DataList;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLSelect;

function alterListToSummaryFields(DataList $list): SQLSelect
{
    $model = $list->dataClass();
    $instance = $model::create();
    $schema = DataObject::getSchema();
    $summaryFields = $instance->summaryFields();
    $dataQuery = $list->dataQuery();

    foreach ($summaryFields as $description => $alias) {
        $references = explode('.', $description);
        $field = array_pop($references);
        $fieldModel = $model;
        if (!empty($references)) {
            $fieldModel = $dataQuery->applyRelation($references);
        }
        $selectedFields[$alias] = $schema->sqlColumnForField(
            $fieldModel,
            $field,
            $dataQuery->applyRelationPrefix($references)
        );
    }
    $sqlQuery = $dataQuery->getFinalisedQuery();
    $sqlQuery->setSelect($selectedFields);

    return $sqlQuery;
}