Level 61
It is complaining that wrong reference has been provided for the post ID. What are the values for $posts and $tag variables?
Dec 24, 2020
10
Level 9
SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`study6_cms`.`post_tag`, CONSTRAINT `post_tag_post_id_foreign` FOREIGN KEY (`post_id`) REFERENCES `posts` (`id`)) (SQL: insert into `po
SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`study6_cms`.`post_tag`, CONSTRAINT `post_tag_post_id_foreign` FOREIGN KEY (`post_id`) REFERENCES `posts` (`id`)) (SQL: insert into `post_tag` (`post_id`, `tag_id`) values (3, 3))
In my localhost post store with tag is properly working. But in server it throw an errror can anyone please tells me what I did wrong...? StoreMethod
public function store(PostStoreRequest $request)
{
$input = $request->validated();
$posts = auth()->user()->posts()->create($input);
if (request('tags') != '') {
$tags = explode(',', request('tags'));
foreach ($tags as $tag_name) {
$tag = Tag::firstOrCreate(['name' => $tag_name]);
}
$posts->tags()->attach($tag);
}
return redirect(route('posts.index'))->withMessage('post 😊 created successfully');
}
blade file
<input type="text" name="tags" class="form-control"
value="{{ old('tags') }}" />
@error('tags')
<small class="form-text text-red">{{ $message }}</small>
@enderror
Level 75
I would change it to this
public function store(PostStoreRequest $request)
{
$post = auth()->user()->posts()->create($request->except('tags'));
if ($request->tags) {
$ids = [];
foreach (($tags = explode(',', $request->tags)) as $tag) {
$ids[] = Tag::firstOrCreate(['name' => $tag]);
}
$post->tags()->attach($ids);
}
$request->session()->flash('message', 'post 😊 created successfully');
return redirect()->route('posts.index');
}
1 like
Level 9
@michaloravec thank you for this code suggestion, I will use this code also....
Level 73
The error means that you are trying to insert a tag with a post_id that doesn't exist as an id in the posts table.
I'm in the process of writing a guide about SQL error message in Laravel and this is the chapter on this error.
The refusal to add or update AKA ERROR 1452 (23000): Cannot add or update a child row:
This error is a distant cousin to the previous error. In this case the foriegn key is preventing us from inserting a record in the books table with an author_id that does not exist in the authors table.
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails
`laraveldb`.`books`, CONSTRAINT `books_author_id_foreign` FOREIGN KEY (`author_id`) REFERENCES `authors` (`id`) ON DELETE CASCADE)
This error migth not be that common in Laravel but I think it's good to know what causes it and how to solve it.
Take this piece of php code in the store method of our Book Controller.
$book = new Book();
$book->title = 'The Wizards First Rule';
$book->author_id = 2;
$book->save();
So the error above tells us that a foreign key constraint fails. That tells us that there is something with our constraint. If we take a look att our authors table and it's contents we will see this.
mysql> select * from authors;
+----+---------------+------------+------------+
| id | name | created_at | updated_at |
+----+---------------+------------+------------+
| 1 | Robert Jordan | NULL | NULL |
+----+---------------+------------+------------+
1 row in set (0.00 sec)
Now since we are using a foreign key constraint it means that our foreign key must exist as a primary key in our authors table. To solve this issue we need either to change the author_id in our insert or create a new author.
So if we create the author first
$author = Author::create(['Terry Goodkind']);
Then we can create the book.
$book = new Book();
$book->title = 'The Wizards First Rule';
$book->author_id = $author->id;
$book->save();
This error is best avoided by using the exists validation rule before trying to insert a new record.
'author_id' => 'required|exists:authors,id'
2 likes
Level 13
Check your migration order that may caused this problem.
2 likes
Level 73
This have nothing to do with migrations to do, That is another error message.
SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint
1 like
Level 9
Level 73
Of course it does since it resets the counters for the primary keys.
Level 1
awesome boss
Level 2
Had a simmilar issue arise thought id share my solution. Instead of running
php artisan migrate:refresh
Which will recreate the database from scratch, try
php artisan migrate:fresh --seed instead.
This will drop all tables in the database and re run the migrate command, preventing the foreign key constraint.
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