如何在laravel 5.1迁移中使用外键

我需要为我的数据库使用外键但我不能这样做,在命令行中运行migration命令后,我收到此错误:

[Illuminate\Database\QueryException] SQLSTATE [HY000]:常规错误:1215无法添加外键约束(SQL:alter table samplesadd constraint s amples_supplier_id_foreign foreign key(supplier_id)references suppliers(id))

[PDOException] SQLSTATE [HY000]:常规错误:1215无法添加外键约束

样本迁移:

Schema::create('samples', function (Blueprint $table) {
            $table->Increments('id',true);
            $table->string('variety',50);
            $table->integer('supplier_id')->unsigned();
            $table->foreign('supplier_id')->references('id')->on('suppliers');
            $table->string('lot_number');
            $table->date('date');
            $table->integer('amount');
            $table->integer('unit_id')->unsigned();
            $table->foreign('unit_id')->references('id')->on('unit');
            $table->string('technical_fact');
            $table->string('comments');
            $table->string('file_address');
            $table->integer('category_id')->unsigned();
            $table->foreign('category_id')->references('id')->on('category');
            $table->timestamps();
        });

供应商迁移:

Schema::create('suppliers', function (Blueprint $table) {
            $table->Increments('id',true);
            $table->string('supplier',50);
            $table->timestamps();
        });

我尝试使用新的迁移样本,但不成功:

Schema::create('samples', function (Blueprint $table) {
                $table->Increments('id',true);
                $table->string('variety',50);
                $table->integer('supplier_id')->unsigned();
                $table->string('lot_number');
                $table->date('date');
                $table->integer('amount');
                $table->integer('unit_id')->unsigned();
                $table->string('technical_fact');
                $table->string('comments');
                $table->string('file_address');
                $table->integer('category_id')->unsigned();
                $table->timestamps();
        });

        Schema::table('samples', function($table) {
            $table->foreign('supplier_id')->references('id')->on('suppliers');
            $table->foreign('unit_id')->references('id')->on('unit');
            $table->foreign('category_id')->references('id')->on('category');
        });

我尝试将主键的长度固定为10,但再次失败

订单很重要.

在尝试引用该表上的列作为约束之前,您需要确保"供应商"表存在.

因此,如果要在创建表时设置外键约束,请确保先创建" 供应商 "迁移,然后再创建" 样本 "迁移:

php artisan make:migration create_suppliers_table --create=suppliers
php artisan make:migration create_samples_table --create=samples

...将架构代码添加到迁移文件中.然后:

php artisan migrate

如果您不想担心创建表的顺序,请先执行create_table迁移,不要使用外键约束,然后再执行一次迁移以添加外键.

php artisan make:migration create_samples_table --create=samples
php artisan make:migration create_suppliers_table --create=suppliers
php artisan make:migration alter_samples_table --table=samples   <-- add your foreign key constraints to this migration file

...将架构代码添加到迁移文件中.然后使用以下方式迁移

php artisan migrate