由于急切加载的工作方式，您无法真正对正在运行的 SQL 执行任何操作来完成您正在寻找的工作。
当您执行Product::with('parent')->get() 时，它会运行两个查询。
首先，它运行查询以获取所有产品：
select * from `products`
接下来，它运行一个查询来获取急切加载的父母：
select * from `products` where `products`.`id` in (?, ?, ?)
参数的数量 (?) 对应于第一个查询的结果数量。检索到第二组模型后，使用 match() 函数将对象相互关联。
为了做你想做的事，你将不得不创建一个新的关系并覆盖match() 方法。这将处理急切加载方面。此外，您需要重写 addConstraints 方法来处理延迟加载方面。
首先，创建一个自定义关系类：
class CustomBelongsTo extends BelongsTo
{
// Override the addConstraints method for the lazy loaded relationship.
// If the foreign key of the model is 0, change the foreign key to the
// model's own key, so it will load itself as the related model.
/**
* Set the base constraints on the relation query.
*
* @return void
*/
public function addConstraints()
{
if (static::$constraints) {
// For belongs to relationships, which are essentially the inverse of has one
// or has many relationships, we need to actually query on the primary key
// of the related models matching on the foreign key that's on a parent.
$table = $this->related->getTable();
$key = $this->parent->{$this->foreignKey} == 0 ? $this->otherKey : $this->foreignKey;
$this->query->where($table.'.'.$this->otherKey, '=', $this->parent->{$key});
}
}
// Override the match method for the eager loaded relationship.
// Most of this is copied from the original method. The custom
// logic is in the elseif.
/**
* Match the eagerly loaded results to their parents.
*
* @param array $models
* @param \Illuminate\Database\Eloquent\Collection $results
* @param string $relation
* @return array
*/
public function match(array $models, Collection $results, $relation)
{
$foreign = $this->foreignKey;
$other = $this->otherKey;
// First we will get to build a dictionary of the child models by their primary
// key of the relationship, then we can easily match the children back onto
// the parents using that dictionary and the primary key of the children.
$dictionary = [];
foreach ($results as $result) {
$dictionary[$result->getAttribute($other)] = $result;
}
// Once we have the dictionary constructed, we can loop through all the parents
// and match back onto their children using these keys of the dictionary and
// the primary key of the children to map them onto the correct instances.
foreach ($models as $model) {
if (isset($dictionary[$model->$foreign])) {
$model->setRelation($relation, $dictionary[$model->$foreign]);
}
// If the foreign key is 0, set the relation to a copy of the model
elseif($model->$foreign == 0) {
// Make a copy of the model.
// You don't want recursion in your relationships.
$copy = clone $model;
// Empty out any existing relationships on the copy to avoid
// any accidental recursion there.
$copy->setRelations([]);
// Set the relation on the model to the copy of itself.
$model->setRelation($relation, $copy);
}
}
return $models;
}
}
创建自定义关系类后，您需要更新模型以使用此自定义关系。在您的模型上创建一个新方法，该方法将使用您的新 CustomBelongsTo 关系，并更新您的 parent() 关系方法以使用此新方法，而不是基本的 belongsTo() 方法。
class Product extends Model
{
// Update the parent() relationship to use the custom belongsto relationship
public function parent()
{
return $this->customBelongsTo('App\Product', 'parent_id', 'id');
}
// Add the method to create the CustomBelongsTo relationship. This is
// basically a copy of the base belongsTo method, but it returns
// a new CustomBelongsTo relationship instead of the original BelongsTo relationship
public function customBelongsTo($related, $foreignKey = null, $otherKey = null, $relation = null)
{
// If no relation name was given, we will use this debug backtrace to extract
// the calling method's name and use that as the relationship name as most
// of the time this will be what we desire to use for the relationships.
if (is_null($relation)) {
list($current, $caller) = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 2);
$relation = $caller['function'];
}
// If no foreign key was supplied, we can use a backtrace to guess the proper
// foreign key name by using the name of the relationship function, which
// when combined with an "_id" should conventionally match the columns.
if (is_null($foreignKey)) {
$foreignKey = Str::snake($relation).'_id';
}
$instance = new $related;
// Once we have the foreign key names, we'll just create a new Eloquent query
// for the related models and returns the relationship instance which will
// actually be responsible for retrieving and hydrating every relations.
$query = $instance->newQuery();
$otherKey = $otherKey ?: $instance->getKeyName();
return new CustomBelongsTo($query, $this, $foreignKey, $otherKey, $relation);
}
}
公平警告，这些都没有经过测试。