Laravel『Call to a Member Function on String』の原因と対処法

Call to a member function save() on string
Call to a member function format() on string
Call to a member function pluck() on string
Call to a member function first() on string

// 例：$user->save() で落ちるなら
logger()->debug('type', [
    'class' => is_object($user) ? get_class($user) : null,
    'type'  => gettype($user),
    'value' => $user,
]);

// 一時的に止めて確認
dd(gettype($user), is_object($user) ? get_class($user) : null, $user);

// NG: $user は "1" のような文字列
$user = $request->input('user_id');
$user->save(); // Call to a member function save() on string

// OK
$user = \App\Models\User::findOrFail($request->input('user_id'));
$user->name = 'New Name';
$user->save();

// routes/web.php
Route::put('/users/{user}', [UserController::class, 'update']);

// Controller
public function update(\Illuminate\Http\Request $request, \App\Models\User $user)
{
    $user->fill($request->only(['name']))->save();
}

// NG: $query はSQL文字列
$query = "select * from users";
$query->where('id', 1); // Call to a member function where() on string

// OK
$query = \App\Models\User::query();
$users = $query->where('id', 1)->get();

// 例：toSql() はSQL文字列を返す
$sql = \App\Models\User::where('id', 1)->toSql(); // string

// NG: $date は "2025-12-15" のような文字列
$date = $request->input('date');
echo $date->format('Y-m-d'); // Call to a member function format() on string

use Illuminate\Support\Carbon;

$date = Carbon::parse($request->input('date'));
echo $date->format('Y-m-d');

// app/Models/Order.php
protected $casts = [
    'ordered_at' => 'datetime',
];

// NG: $payload はJSON文字列
$payload = $request->input('payload'); // '{"name":"taro"}'
$name = $payload->get('name');         // Call to a member function get() on string

$payload = json_decode($request->input('payload'), true); // 配列化
$name = $payload['name'] ?? null;

// app/Models/Log.php
protected $casts = [
    'payload' => 'array',
];

// NG
$user = \App\Models\User::findOrFail($id); // object
$user = $request->input('user');          // string に上書き
$user->save();                            // Call to a member function save() on string

// OK
$user = \App\Models\User::findOrFail($id);
$userName = $request->input('user');
$user->name = $userName;
$user->save();

// 例：emailは文字列
$email = \App\Models\User::where('id', 1)->pluck('email')->first(); // string
$email->lower(); // Call to a member function lower() on string

use Illuminate\Support\Str;

$email = \App\Models\User::where('id', 1)->value('email'); // string
$lower = Str::lower($email);

$emails = \App\Models\User::whereIn('id', [1,2])->pluck('email'); // Collection

// NG: items が "a,b,c" のような文字列
$items = $request->input('items');
$items->map(...); // Call to a member function map() on string

// 例：items は配列で来る前提
$request->validate([
    'items' => ['required', 'array'],
    'items.*' => ['string'],
]);

$items = collect($request->input('items')); // Collection化

$items = $request->input('items');

if (is_string($items)) {
    $items = array_filter(array_map('trim', explode(',', $items)));
}

$items = collect($items);

$request->validate([
    'user_id' => ['required', 'integer', 'exists:users,id'],
    'date' => ['required', 'date'],
    'payload' => ['nullable', 'json'],
]);

# 1) ID文字列をモデルだと思う
# NG
$user = $request->input('user_id');
$user->save();

# OK
$user = User::findOrFail($request->input('user_id'));
$user->save();


# 2) 日付文字列に format()
# NG
$date = $request->input('date');
$date->format('Y-m-d');

# OK
$date = Carbon::parse($request->input('date'));
$date->format('Y-m-d');


# 3) JSON文字列をオブジェクト扱い
# NG
$payload = $request->input('payload'); // string
$payload->get('name');

# OK
$payload = json_decode($request->input('payload'), true);
$payload['name'] ?? null;


# 4) 変数の上書き
# NG
$user = User::findOrFail($id);
$user = $request->input('user');
$user->save();

# OK
$user = User::findOrFail($id);
$userName = $request->input('user');
$user->name = $userName;
$user->save();