添加 2 个外键时 Laravel 迁移错误

Question

我正在使用 Laravel 迁移来创建我的 MySQL 数据库，并且有两个表论文和答案，并且需要使用外键连接两个表。 我有paper_id以及question_no作为外键。 但是在添加外键时出现错误。 我的纸表和答案表的迁移

Schema::create('exampapers', function (Blueprint $table) {
        $table->engine = 'InnoDB';
        $table->increments('id');
        $table->integer('paper_id');
        $table->integer('question_no');
        $table->text('question');
        $table->string('answer1');
        $table->string('answer2');
        $table->string('answer3');
        $table->string('answer4');
        $table->integer('answerC');
        $table->string('knowarea');
        $table->timestamps();
        $table->index(['paper_id','question_no']);

});

Schema::create('answers', function (Blueprint $table) {
        $table->engine = 'InnoDB';
        $table->increments('id');
        $table->integer('paper')->unsigned();
        $table->integer('question')->unsigned();
        $table->integer('answers');
        $table->timestamps();
});

这是我创建外键的代码，

Schema::table('answers',function($table){
        $table->foreign('paper')->references('paper_id')->on('exampapers');
        $table->foreign('question')->references('question_no')->on('exampapers');
});

我通过 php artisan 得到的错误是，

Illuminate\\Database\\QueryException : SQLSTATE[HY000]: General error: 1005 Can't create table exam_paper 。 #sql-b88_630 (errno: 150 "外键约束#sql-b88_630不正确") (SQL: alter table answers添加约束answers_paper_foreign外键 ( paper ) 参考exampapers ( paper_id ))

我参考了其他大部分帖子，并且已经尝试过unsignedInteger()数据类型，在创建外键之前运行表创建。

我的代码做错了什么？

Answer 1

您需要添加->unsigned()->nullable()->index(); 在两列中（即在paper_id和exampapers表中的question ）。

尝试在exampapers表中添加如下exampapers ：

$table->integer('paper_id')->unsigned()->nullable()->index();
$table->integer('question_no')->unsigned()->nullable()->index();

现在运行php artisan migrate并修复问题！

希望这对你有帮助！

Answer 2

您还需要使exampapers表中的密钥未签名：

$table->integer('paper_id')->unsigned();

或者：

$table->insignedInteger('paper_id');

或者从外键定义中删除unsigned()方法：

$table->integer('paper');

Answer 3

我对您的迁移代码进行了一些编辑。 希望这会奏效

Schema::create('exampapers', function (Blueprint $table) {
        $table->engine = 'InnoDB';
        $table->increments('id');
        $table->integer('paper_id')->unsigned()->index();
        $table->integer('question_no')->unsigned()->index();
        $table->text('question');
        $table->string('answer1');
        $table->string('answer2');
        $table->string('answer3');
        $table->string('answer4');
        $table->integer('answerC');
        $table->string('knowarea');
        $table->timestamps();
        //$table->index(['paper_id','question_no']);

    });

Schema::create('answers', function (Blueprint $table) {
        $table->engine = 'InnoDB';
        $table->increments('id');
        $table->integer('paper')->unsigned()->index();
        $table->integer('question')->unsigned()->index();
        $table->integer('answers');
        $table->timestamps();
    });


Schema::table('answers',function($table){
        $table->foreign('paper')->references('paper_id')->on('exampapers');
        $table->foreign('question')->references('question_no')->on('exampapers');
    });