如果用户不存在，如何从用户表中检索用户信息并处理错误？

Question

我在一个传销网站上工作，试图在刀片视图中拉出二叉树中的用户，它适用于前三个用户，因为查询中存在这样的用户ID。但对于没有子代的用户，它会抛出错误。如果用户不存在，我如何从用户表中检索用户信息并处理错误？

我的路线：

Route::get('{id}/genealogy-tree', 'UsersController@show_genealogy')->name('genealogy-tree');

我的控制器：

public function show_genealogy($id)
{
    // $headuser = User::findOrFail($id);
    // $headuser_id = $headuser->id;
    if (User::findOrFail($id)->exists()) {
        $headuser = User::findOrFail($id);
        $headuser_id = $headuser->id;
    } else {
        $headuser = null;
        $headuser_id = null;

    }
    #-------------------------------------------------------
    if (User::where('l_id',  $headuser_id)->exists()) {
        $lfu = User::where('l_id',  $headuser_id)->first();
    } else {
        $lfu = null;
    }
    if (User::where('r_id',  $headuser_id)->exists()) {
        $rfu = User::where('r_id',  $headuser_id)->first();
    } else {
        $rfu = null;
    }

    // return view('users.genealogy-tree', compact('headuser','lfu','rfu'));
    #--------------------------------------------------------
    if (User::where('l_id',  $lfu->id)) {
        $lsu = User::where('l_id',  $lfu->id)->first();
    } else {
        $lsu = null;
    }       
    
    if (User::where('r_id',  $lfu->id)->exists()) {
        $rsu = User::where('r_id', $lfu->id)->first();
    }  else {
        $rsu = null;
    } 

    if (User::where('l_id',  $rfu->id)->exists()) {
        $ltu = User::where('l_id',  $rfu->id)->first();
    } else {
        $ltu = null;
    } 
    if (User::where('r_id',  $rfu->id)->exists()) {
        $rtu = User::where('r_id',  $rfu->id)->first();
    } else {
        $rtu = null;
    } 
    #--------------------------------------------------------

    return view('users.genealogy-tree', compact('headuser','lfu','rfu','lsu','rsu','ltu','rtu'));
    // return $lfu;
}

我的观点是：

<div class="table-responsive">
<table class="table" style="align:center; border:o; text-align:center">
    <tr height="150" >
        <td></td>
        @isset($headuser)
        <td colspan="6"> <a href="{{route('genealogy-tree', $headuser->id)}}"><i class="fa fa-user fa-4x" style="color: #45fc03 !important; font-size: 1000%;"></i>
        <div class="tree_div"> 
        <p>User Name: {{$headuser->name ? $headuser->name : 'No Record'}}</p>
        <p>Network Worth: {{$headuser->network_bonus ? $headuser->network_bonus : 'No Record'}}</p>
        <p>Donations: {{$headuser->donation_sum ? $headuser->donation_sum : 'No Record'}}</p>
        <p>Current Level: {{$headuser->level ? $headuser->level : 'No Record'}}</p>     
        </div></a>
        </td>
        @else
        <td colspan="6"> <a href="#"><i class="fa fa-user fa-4x" style="color: gray !important; font-size: 1000%;"></i>
        <div class="tree_div">
            <br> 
        <p>{{'No User'}}</p>   
        </div></a>
        @endisset
        <td></td>
    </tr>

    <tr height="150">
        @isset($lfu)
        <td colspan="4"> <a href="{{route('genealogy-tree', $lfu->id)}}"><i class="fa fa-user fa-4x" style="color: #b6fc03 !important; font-size: 700%;"></i>
        <div class="tree_div"> 
        <p>User Name: {{$lfu->name ? $lfu->name : 'No Record'}}</p>
        <p>Network Worth: {{$lfu->network_bonus ? $lfu->network_bonus : 'No Record'}}</p>
        <p>Donations: {{$lfu->donation_sum ? $lfu->donation_sum : 'No Record'}}</p>
        <p>Current Level: {{$lfu->level ? $lfu->level : 'No Record'}}</p>     
        </div></a>
        </td>
        @else
        <td colspan="4"> <a href="#"><i class="fa fa-user fa-4x" style="color: gray !important; font-size: 700%;"></i>
        <div class="tree_div">
            <br> 
        <p>{{'No User'}}</p>   
        </div></a>
        @endisset
        @isset($rfu)
        <td colspan="4"> <a href="{{route('genealogy-tree', $rfu->id)}}"><i class="fa fa-user fa-4x" style="color: #b6fc03 !important; font-size: 700%;"></i>
        <div class="tree_div"> 
        <p>User Name: {{$rfu->name ? $rfu->name : 'No Record'}}</p>
        <p>Network Worth: {{$rfu->network_bonus ? $rfu->network_bonus : 'No Record'}}</p>
        <p>Donations: {{$rfu->donation_sum ? $rfu->donation_sum : 'No Record'}}</p>
        <p>Current Level: {{$rfu->level ? $rfu->level : 'No Record'}}</p>     
        </div></a>
        </td>
        @else
        <td colspan="4"> <a href="#"><i class="fa fa-user fa-4x" style="color: gray !important; font-size: 700%;"></i>
        <div class="tree_div">
            <br> 
        <p>{{'No User'}}</p>   
        </div></a>
        @endisset
    </tr>

     <tr height="150" style="color: #f4fc03; font-size: 130%;">
       
        @isset($lsu)
        <td colspan="2"> <a href="{{route('genealogy-tree', $lsu->id)}}"><i class="fa fa-user fa-4x" style="color: #f4fc03 !important;"></i>
        <div class="tree_div"> 
        <p>User Name: {{$lsu->name ? $lsu->name : 'No Record'}}</p>
        <p>Network Worth: {{$lfu->network_bonus ? $lfu->network_bonus : 'No Record'}}</p>
        <p>Donations: {{$lsu->donation_sum ? $lsu->donation_sum : 'No Record'}}</p>
        <p>Current Level: {{$lsu->level ? $lsu->level : 'No Record'}}</p>     
        </div></a>
        </td>
        @else
        <td colspan="2"> <a href="#"><i class="fa fa-user fa-4x" style="color: gray !important; font-size: 700%;"></i>
        <div class="tree_div">
            <br> 
        <p>{{'No User'}}</p>   
        </div></a>
        @endisset
        @isset($rsu)
        <td colspan="2"> <a href="{{route('genealogy-tree', $rsu->id)}}"><i class="fa fa-user fa-4x" style="color: #b6fc03 !important;"></i>
        <div class="tree_div"> 
        <p>User Name: {{$rsu->name ? $rsu->name : 'No Record'}}</p>
        <p>Network Worth: {{$rsu->network_bonus ? $rsu->network_bonus : 'No Record'}}</p>
        <p>Donations: {{$rsu->donation_sum ? $rsu->donation_sum : 'No Record'}}</p>
        <p>Current Level: {{$rsu->level ? $rsu->level : 'No Record'}}</p>     
        </div></a>
        </td>
        @else
        <td colspan="2"> <a href="#"><i class="fa fa-user fa-4x" style="color: gray !important; font-size: 700%;"></i>
        <div class="tree_div">
            <br> 
        <p>{{'No User'}}</p>   
        </div></a>
        @endisset

        @isset($ltu)
        <td colspan="2"> <a href="{{route('genealogy-tree', $ltu->id)}}"><i class="fa fa-user fa-4x" style="color: #f4fc03 !important;"></i>
        <div class="tree_div"> 
        <p>User Name: {{$ltu->name ? $ltu->name : 'No Record'}}</p>
        <p>Network Worth: {{$ltu->network_bonus ? $ltu->network_bonus : 'No Record'}}</p>
        <p>Donations: {{$ltu->donation_sum ? $ltu->donation_sum : 'No Record'}}</p>
        <p>Current Level: {{$ltu->level ? $ltu->level : 'No Record'}}</p>     
        </div></a>
        </td>
        @else
        <td colspan="2"> <a href="#"><i class="fa fa-user fa-4x" style="color: gray !important; font-size: 700%;"></i>
        <div class="tree_div">
            <br> 
        <p>{{'No User'}}</p>   
        </div></a>
        @endisset
        @isset($rtu)
        <td colspan="2"> <a href="{{route('genealogy-tree', $rtu->id)}}"><i class="fa fa-user fa-4x" style="color: #b6fc03 !important;"></i>
        <div class="tree_div"> 
        <p>User Name: {{$rtu->name ? $rtu->name : 'No Record'}}</p>
        <p>Network Worth: {{$rtu->network_bonus ? $rtu->network_bonus : 'No Record'}}</p>
        <p>Donations: {{$rtu->donation_sum ? $rtu->donation_sum : 'No Record'}}</p>
        <p>Current Level: {{$rtu->level ? $rtu->level : 'No Record'}}</p>     
        </div></a>
        </td>
        @else
        <td colspan="2"> <a href="#"><i class="fa fa-user fa-4x" style="color: gray !important; font-size: 700%;"></i>
        <div class="tree_div">
            <br> 
        <p>{{'No User'}}</p>   
        </div></a>
        @endisset

    </tr>
   


    <!-- <tr height="150" style="color: #fcb603; font-size: 100%;">
        <td> <i class="fa fa-user fa-4x"></i></td>
        <td> <i class="fa fa-user fa-4x"></i></td>
        <td> <i class="fa fa-user fa-4x"></i></td>
        <td> <i class="fa fa-user fa-4x"></i></td>
        <td> <i class="fa fa-user fa-4x"></i></td>
        <td> <i class="fa fa-user fa-4x"></i></td>
        <td> <i class="fa fa-user fa-4x"></i></td>
        <td> <i class="fa fa-user fa-4x"></i></td>
    </tr> -->
    

</table>

  enter code here

Answer 1

当找不到记录时，first()返回null，您只需在使用变量之前检查是否为null。

您可以使用optional(..)或null函数访问器$var?->function(…)来避免null问题

控制器中的问题是因为您首先尝试查找将$headuser_id与代码匹配的用户：

if (User::where('l_id',  $headuser_id)->exists()) {
    $lfu = User::where('l_id',  $headuser_id)->first();
} else {
    $lfu = null;

您可以将其简化为：

$lfu = User::where('l_id',  $headuser_id)->first();

As first将返回用户或null (如果它们不存在)。

但是您的错误是由代码尝试使用$lfu->id而引起的，而$lfu可能是null

if (User::where('l_id',  $lfu->id)) { ...
                         ^^^^^^^^

您需要检查empty($lfu)或在if中分配变量，当您找到用户时，您可以使用他们的id来搜索其他用户：

$lsu = null;
$ltu = null;

if ($lfu = User::where('l_id',  $headuser_id)->first()) {
    $lsu = User::where('l_id',  $lfu->id)->first();
    $ltu = User::where('l_id',  $rfu->id)->first();
}