我在Laravel模型上有一个雄辩的关系,它是动态的——也就是说,特定数据库字段的值决定了哪个模型将被加载。当我第一次实例化模型实例并引用关系时,我能够很好地加载这种关系,但是当我渴望加载这种关系时,它就不起作用了。
具体来说,我有一个Products
模型。该产品可能是也可能不是另一个产品的父产品。如果产品的parent_id
设置为0
,则该产品被视为父部分(无论是否有子部分)。如果parent_id
设置为不同产品的id,则该产品是子产品。我需要能够访问产品::('父')
,并知道父
关系将返回其本身(是的,重复的数据)或不同的产品,如果它是一个孩子。
以下是我到目前为止的关系:
public function parent()
{
if ($this->parent_id > 0) {
return $this->belongsTo('App\Product', 'parent_id', 'id');
} else {
return $this->belongsTo('App\Product', 'id', 'id');
}
}
当我急于加载时,$this-
在加载关系之前,有没有办法访问模型的属性?在返回关系之前,我考虑过使用一个单独的查询,但我意识到我甚至无法访问产品的id来运行该查询。
如果这是不可能的,有什么其他方法来解决这类问题?这似乎不能通过传统的多态关系来解决。我只有两个可能的想法:
belongsTo
关系中添加某种约束,在该关系中动态确定外键李> 老实说,我不知道如何实现这两个目标。我这样做对吗?有什么是我忽略的吗?
经过深入思考后,我认为最简单的问题是:有没有办法在运行时为关系本身内部的关系动态选择外键?当我调用关系时,我的用例不允许我使用急切的加载约束——约束需要应用于关系本身。
由于急切加载的工作方式,您无法对正在运行的SQL执行任何操作来完成所需的操作。
当您使用('父')执行产品::时-
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,以获取急切加载的父级:
select * from `products` where `products`.`id` in (?, ?, ?)
参数的数量(?
)对应于第一次查询的结果数量。检索到第二组模型后,将使用match()
函数将对象彼此关联起来。
为了做你想做的事情,你必须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特性。
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,需要更新模型以使用此自定义关系。在模型上创建一个新方法,该方法将使用新的CustomBelongsTo
关系,并更新parent()
关系方法以使用此新方法,而不是基本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);
}
}
公平的警告,这些都没有经过测试。