php - 如何在 Laravel 5.1 迁移中使用外键

Question

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

[Illuminate\Database\QueryException] SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table samples add constraint s amples_supplier_id_foreign foreign key (supplier_id) references suppliers (id))

[PDOException] SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint

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();
        });

我尝试通过新的样本迁移来实现这一点，但没有成功:

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

Answer 1

订单很重要。

在尝试引用该表上的列作为约束之前，您需要确保您的“供应商”表存在。

因此，如果您想在创建表时设置外键约束，请确保先创建“suppliers”迁移，然后再创建“samples”迁移之后:

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

...将模式代码添加到您的迁移文件中。然后:

php artisan migrate

---

如果您不想担心表的创建顺序，那么首先执行您的 create_table 迁移，没有外键约束，然后执行额外的迁移以添加您的外键。

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

...将模式代码添加到您的迁移文件中。然后迁移使用:

php artisan migrate