最好的解决方案之一是使用firstOrNew或firstOrCreate方法。文档中有更多关于这两者的详细信息。

$user = User::where('email', '=', Input::get('email'))->first();
if ($user === null) {
   // user doesn't exist
}

可以写成

if (User::where('email', '=', Input::get('email'))->first() === null) {
   // user doesn't exist
}

这将返回true或false，而不分配临时变量，如果这是你在原始语句中使用$user的全部目的。

如果你想插入一个唯一的记录，你可以使用laravel验证:

$validated = $request->validate([
    'title' => 'required|unique:usersTable,emailAddress|max:255',
]);

但是你也可以用这些方法:

1:

if (User::where('email',  $request->email)->exists())
{
  // object exists
} else {
  // object not found
}

2:

$user = User::where('email',  $request->email)->first();

if ($user)
{
  // object exists
} else {
  // object not found
}

3:

$user = User::where('email',  $request->email)->first();

if ($user->isNotEmpty())
{
  // object exists
} else {
  // object not found
}

4:

$user = User::where('email',  $request->email)->firstOrCreate([
      'email' => 'email'
],$request->all());

Laravel 6或顶部:写表名，然后给出where子句条件，例如where('id'， $request->id)

 public function store(Request $request)
    {

        $target = DB:: table('categories')
                ->where('title', $request->name)
                ->get()->first();
        if ($target === null) { // do what ever you need to do
            $cat = new Category();
            $cat->title = $request->input('name');
            $cat->parent_id = $request->input('parent_id');
            $cat->user_id=auth()->user()->id;
            $cat->save();
            return redirect(route('cats.app'))->with('success', 'App created successfully.');

        }else{ // match found 
            return redirect(route('cats.app'))->with('error', 'App already exists.');
        }

    }

if ($u = User::where('email', '=', $value)->first())
{
   // do something with $u
   return 'exists';
} else {
  return 'nope';
}

可以用try/catch吗

->get()仍然返回一个空数组

$email = User::find($request->email);
If($email->count()>0)
<h1>Email exist, please make new email address</h1>
endif