framework/db/ActiveQueryTrait.php
public function findWith($with, &$models)
    {
        $primaryModel = reset($models);
        if (!$primaryModel instanceof ActiveRecordInterface) {
            /* @var $modelClass ActiveRecordInterface */
            $modelClass = $this->modelClass;
            $primaryModel = $modelClass::instance();
        }
        $relations = $this->normalizeRelations($primaryModel, $with);
        /* @var $relation ActiveQuery */
        foreach ($relations as $name => $relation) {
            if ($relation->asArray === null) {
                // inherit asArray from primary query
                $relation->asArray($this->asArray);
            }
            $relation->populateRelation($name, $models);
        }
    }
public function findWith($with, &$models)
    {
        $primaryModel = reset($models);
        if (!$primaryModel instanceof ActiveRecordInterface) {
            /* @var $modelClass ActiveRecordInterface */
            $modelClass = $this->modelClass;
            $primaryModel = $modelClass::instance();
        }
        $relations = $this->normalizeRelations($primaryModel, $with);
        /* @var $relation ActiveQuery */
        foreach ($relations as $name => $relation) {
            if ($relation->asArray === null) {
                // inherit asArray from primary query
                $relation->asArray($this->asArray);
            }
            $relation->populateRelation($name, $models);
        }
    }
Finds records corresponding to one or multiple relations and populates them into the primary models.
@param array $with a list of relations that this query should be performed with. Please
refer to [[with()]] for details about specifying this parameter.
@param array|ActiveRecord[] $models the primary models (can be either AR instances or arrays)