Laravel種子：完整性約束違規：1452不能添加或更新子行：外鍵約束

Question

我的Twitter構建克隆應用程序中使用Laravel5.4和While referring to this

現在我想播種數據庫測試數據失敗

在我端子輸入php artisan db:seed --class=TweetsTableSeeder 遇到錯誤

Integrity constraint violation: 1452 Cannot add 
    or update a child row: a foreign key constraint fails (`twitter`. 
    `tweets`, CONSTRAINT `tweets_user_id_foreign` FOREIGN KEY (`user_ 
    id`) REFERENCES `users` (`id`) ON DELETE CASCADE) 

我讀了錯誤，並試圖瞭解，但我沒有很好的效果。 我正在查看官方文檔，但因爲初學者而無法理解。

所以請幫我

2017_07_09_create_tweets_table

<?php 

use Illuminate\Support\Facades\Schema; 
use Illuminate\Database\Schema\Blueprint; 
use Illuminate\Database\Migrations\Migration; 

class CreateTweetsTable extends Migration 
{ 
    /** 
    * Run the migrations. 
    * 
    * @return void 
    */ 
    public function up() 
    { 
     Schema::create('tweets', function (Blueprint $table) { 
      $table->increments('id'); 
      $table->integer('user_id')->unsigned()->index(); 
      $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade'); 
      $table->string('body', 140); 
      $table->timestamps(); 
     }); 
    } 

    /** 
    * Reverse the migrations. 
    * 
    * @return void 
    */ 
    public function down() 
    { 
     Schema::dropIfExists('tweets'); 
    } 
} 

Tweet.php

<?php 

namespace App; 

use Illuminate\Database\Eloquent\Model; 

class Tweet extends Model 
{ 
    protected $fillable = [ 
     'user_id', 'body', 
    ]; 
} 

TweetsTableSeeder

<?php 

use App\Tweet; 
use Illuminate\Database\Seeder; 

class TweetsTableSeeder extends Seeder 
{ 
    /** 
    * Run the database seeds. 
    * 
    * @return void 
    */ 
    public function run() 
    { 
     factory(Tweet::class, 10)->create([ 
     'user_id' => 2 
     ]); 
    } 
} 

ModelFactory.php

<?php 

/* 
|-------------------------------------------------------------------------- 
| Model Factories 
|-------------------------------------------------------------------------- 
| 
| Here you may define all of your model factories. Model factories give 
| you a convenient way to create models for testing and seeding your 
| database. Just tell the factory how a default model should look. 
| 
*/ 

/** @var \Illuminate\Database\Eloquent\Factory $factory */ 
$factory->define(App\User::class, function (Faker\Generator $faker) { 
    static $password; 

    return [ 
     'name' => $faker->name, 
     'email' => $faker->unique()->safeEmail, 
     'password' => $password ?: $password = bcrypt('secret'), 
     'remember_token' => str_random(10), 
    ]; 
}); 

$factory->define(App\Tweet::class, function (Faker\Generator $faker) { 
    return [ 
     'body' => $faker->realText(140), 
    ]; 
}); 

Answer 1

完整性約束違規：1452不能添加或更新一個孩子 行，外鍵約束失敗（twitter。 tweets，約束 tweets_user_id_foreign外鍵（user_ id）參考文獻users （id）ON DELETE CASCADE）

上述錯誤只是意味着你正在試圖seed（插入）在tweets表中的值並且該值是不可在母公司users表中找到。

通俗地說，當兩個表共享外鍵關係時，只能將該值插入父表中已存在於父表中的值。在你的情況下，你違反了上述規定。