php - LARAVEL:MYSQL:违反完整性约束:1452 无法添加或更新子行:外键约束失败

Question

我正在尝试将外键应用于列 user_id，与表 users 的 ID 相关

我已经尝试通过迁移和工作台来完成，但这个错误不断出现:

Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails

这是mysql:

ALTER TABLE `dh_booky`.`books` 

ADD CONSTRAINT `books_user_id_foreign`

  FOREIGN KEY (`user_id`)

  REFERENCES `dh_booky`.`users` (`id`)

  ON DELETE NO ACTION

  ON UPDATE NO ACTION;

第一次迁移书籍:

 public function up()
    {
        Schema::create('books', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->bigInteger('title_id')->unsigned();
            $table->foreign('title_id')->references('id')->on('titles');
            $table->bigInteger('author_id')->unsigned();
            $table->foreign('author_id')->references('id')->on('authors');
            $table->string('image')->nullable();

        });
    }

更新迁移书籍:

class UpdateBooksTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::table('users', function (Blueprint $table) {
        $table->bigInteger('user_id')->unsigned();
        $table->foreign('user_id')->references('id')->on('users');
        //php artisan make:migration update_votes_table



});

用户迁移:

public function up()
    {
        Schema::create('users', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->timestamps();
            $table->string('name');
            $table->string('email')->unique();
            $table->string('password');
            $table->rememberToken();
        });
    }

Answer 1

似乎您正在更新 users 表而不是 UpdateBooksTable 迁移中的 books 表。

您可能已经在 books 表中有了数据。因此，现有书籍未引用 user_id，这是导致错误的原因。

您可以将 nullable() 添加到 user_id，以便现有图书的 user_id 为空。

class UpdateBooksTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        //Seem you are updating books table. change users to books 
        Schema::table('users', function (Blueprint $table) {
            $table->bigInteger('user_id')->unsigned()->nullable();
            $table->foreign('user_id')->references('id')->on('users');
        });
    }
}