Can indexby be used on associations directly in the query? - cakephp-3.0

Question

I have a number of situations where I need to cross-reference various records by ID, and find it's easiest to do so when the array is indexed by that ID. For example, Divisions hasMany Teams, Divisions hasMany Games, and Games belongTo HomeTeam and AwayTeam. When I want to read all of the teams and games in a division, I do something like this:
$division = $this->Divisions->get($id, [
'contain' => ['Teams', 'Games']
]);
I don't do
$division = $this->Divisions->get($id, [
'contain' => ['Teams', 'Games' => ['HomeTeam', 'AwayTeam']]
]);
because it seems that would increase memory requirements, especially when I'm further containing other models (People, etc.) in the Teams. So, instead I do
$division->teams = collection($division->teams)->indexBy('id')->toArray();
after the get to reindex that array, and then when I'm iterating through $division->games, to get the home team record I use $division->teams[$game->home_team_id]. This is all well and good (except that it sets the teams property as being dirty, a minor inconvenience).
But it seems that the queryBuilder functionality of the ORM is pretty magical, and I know that I can do
$teams = $this->Divisions->Teams->find()
->where(['division_id' => $id])
->indexBy('id')
->toArray();
to get an array of teams indexed how I want, so I'm wondering if there's some way to include indexBy on the associations. I tried
$division = $this->Divisions->get($id, [
'contain' => [
'Teams' => [
'queryBuilder' => function (Query $q) {
return $q->indexBy('id');
},
],
'Games',
]
]);
but, unsurprisingly, this didn't work. Any ideas?

Answer 1

Just for the record, guess you know this already, indexBy() doesn't belong to the query, but to the result set, so being able to call it requires the query to be executed first. It's not possible to use this for an association query builder, as it must return a query, not a result set.
While it would be possible to use result formatters for the associations and modify the result set accordingly, the problem is that the result set will hold all team results for all divisions, and when the team entities are being distributed on the various division entities that they belong to, the arrays will be "reindexed", respectively, the arrays will be populated without respect to the indices of the result set, so long story short, that won't work.
Global result formatter
However, a result formatter for the main query should work fine, and as you probably already figured, you can simply reset the dirty state afterwards in case it causes any problems, something like
$division = $this->Divisions
->find()
->contain([
'Teams'
])
->where([
'Divisions.id' => $id
])
->formatResults(function($results) {
/* #var $results \Cake\Datasource\ResultSetInterface|\Cake\Collection\CollectionInterface */
return $results
->map(function ($row) {
if (isset($row['teams'])) {
$row['teams'] = collection($row['teams'])->indexBy('id')->toArray();
}
if ($row instanceof EntityInterface) {
$row->dirty('teams', false);
}
return $row;
});
})
->firstOrFail();
Custom association and association specific result formatters
Another option would be to use a custom association class, which overrides ExternalAssociationTrait::_buildResultMap(), so that it respects the indices of the result set, as this is where the problem starts.
By default the associated entities are fetched from the result set and appended to a new array, which is later assigned to the respective association property on the entity the results belong to. So this is where the the keys from the possible custom indexed result set are being lost.
Here's an example, the change is really small, but I'm not sure about possible side effects!
src/Model/Association/IndexAwareHasMany.php
namespace App\Model\Association;
use Cake\ORM\Association\HasMany;
class IndexAwareHasMany extends HasMany
{
protected function _buildResultMap($fetchQuery, $options)
{
$resultMap = [];
$key = (array)$options['foreignKey'];
// grab the index here
foreach ($fetchQuery->all() as $index => $result) {
$values = [];
foreach ($key as $k) {
$values[] = $result[$k];
}
// and make use of it here
$resultMap[implode(';', $values)][$index] = $result;
}
return $resultMap;
}
}
Original: https://github.com/cakephp/...ORM/Association/ExternalAssociationTrait.php#L109
Now you must of course make use of the new association, to simplify it for this example, let's just override the table class' default hasMany() method
public function hasMany($associated, array $options = [])
{
$options += ['sourceTable' => $this];
$association = new \App\Model\Association\IndexAwareHasMany($associated, $options);
return $this->_associations->add($association->name(), $association);
}
And now, finally, you could use a result formatter for the association:
$division = $this->Divisions->get($id, [
'contain' => [
'Teams' => [
'queryBuilder' => function (Query $query) {
return $query
->formatResults(function($results) {
/* #var $results \Cake\Datasource\ResultSetInterface|\Cake\Collection\CollectionInterface */
return $results->indexBy('id');
});
}
],
'Games',
]
]);