拉拉维尔 5.6.26v

通过主键(电子邮件或id)查找现有记录

    $user = DB::table('users')->where('email',$email)->first();

然后

      if(!$user){
             //user is not found 
      }
      if($user){
             // user found 
      }

包括“use DB”和表名user变成复数，使用上面的查询，就像user变成users

if($user->isEmpty()){
    // has no records
}

Eloquent使用集合。 参见以下链接:https://laravel.com/docs/5.4/eloquent-collections

$user = User::where('email', '=', Input::get('email'))->first();
if ($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。

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.');
        }

    }

最简单的方法

    public function update(Request $request, $id)
{


    $coupon = Coupon::where('name','=',$request->name)->first(); 

    if($coupon->id != $id){
        $validatedData = $request->validate([
            'discount' => 'required',   
            'name' => 'required|unique:coupons|max:255',      
        ]);
    }


    $requestData = $request->all();
    $coupon = Coupon::findOrFail($id);
    $coupon->update($requestData);
    return redirect('admin/coupons')->with('flash_message', 'Coupon updated!');
}

我认为下面的方法是达到同样目的的最简单的方法:

    $user = User::where('email', '=', $request->input('email'))->first();
    if ($user) {
       // user exist!
    }else{
       // user does not exist
    }