Laravel不能急切加载MorphOne的特定字段

Question

我有一个分配模型，它包含一个MorphOne到一个MessageThread模型。

class Assignment extends Model
{
/**
* @return MorphOne<AppMessageThread>
*/
public function messageThread(): MorphOne
{
return $this->morphOne("AppMessageThread", "messageable");
}
}

class MessageThread extends Model
{
/**
* The attributes that are mass assignable.
*
* @var string[]
*/
protected $fillable = [
"messageable_id",
"messageable_type",
"status",
"account_id",
"public",
"title",
"direct",
];
public function users(): BelongsToMany
{
return $this->belongsToMany(
"AppUser",
"message_thread_user",
)->withPivot("read");
}
public function messages(): HasMany
{
return $this->hasMany("AppMessage");
}
public function messageable(): MorphTo
{
return $this->morphTo();
}
}

下面的代码为每个赋值加载MessageThread关系

$assignments = AppAssignment::where("account_id", $account_id)
->with("messageThread")
->withCount(["logs", "messages"])
->paginate(30);

List of objects: [
{
"id": 378065,
...,
"message_thread": {
"id": 159809,
...,
"messageable_type": "App\Assignment",
"created_at": "2022-08-26T20:36:38.000000Z",
"updated_at": "2022-08-26T20:36:38.000000Z",
}
}
]

然而，我只想加载消息线程的id。我不需要加载整个模型。当我搜索如何做到这一点时，看起来我需要用query来替换:

$assignments = AppAssignment::where("account_id", $account_id)
->with("messageThread:id")
->withCount(["logs", "messages"])
->paginate(30);

我还尝试过做一个查询选择器，据我所知，这是做messageThread:id的更详细的方法。

$assignments = AppAssignment::where("account_id", $account_id)
->with(["messageThread" => function ($query) {
$query->select("id");
}])->withCount(["logs", "messages"])
->paginate(30);

问题是，我最终与JSON响应中的message_thread的空值:

[
{
"id": 378065,
...,
"message_thread": null
},
]

我知道问题不在于MessageThread不存在，因为如果我不指定列，它加载完全没问题。

我试着搜索这类错误，但是一无所获。

Answer 1

messageable_id需要包含在select中，以便匹配Assignment和MessageThread模型

$assignments = AppAssignment::where("account_id", $account_id)
->with(["messageThread" => function ($query) {
$query->select("message_thread.id, message_thread.messageable_id");
}])
->withCount(["logs", "messages"])
->paginate(30);

演职表:https://laracasts.com/discuss/channels/eloquent/select-columns-on-relationship-tables?page=1&replyId=755706