[英]Nullable column as foreign key in laravel
I have customers table in the database. 我在数据库中有customer表。 A customer is associated with an industry.
客户与行业相关联。 Because of the requirement,
industry_id
is null when customer is created. 由于要求,在创建客户时,
industry_id
为null。 later it will be updated and correct industry id is added. 稍后它将被更新并添加正确的行业ID。
Now, when I want to add this column as foreign key it shows following error. 现在,当我想将此列添加为外键时,它会显示以下错误。
SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table
customers
add constraintcustomers_industry_id_foreign
foreign key (industry_id
) referencesindustries
SQLSTATE [HY000]:一般错误:1215无法添加外键约束(SQL:alter table
customers
add constraintcustomers_industry_id_foreign
外键(industry_id
)引用industries
(id
))(
id
))
I have following code in customers migration. 我在客户迁移中有以下代码。
<?php
use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;
class CreateCustomersTable extends Migration
{
/**
* Run the migrations.
*
* @return void
*/
public function up()
{
Schema::create('customers', function (Blueprint $table) {
$table->bigIncrements('id')->comment="Customer Identifier";
$table->bigInteger('customer_category_id')->unsigned()->comment="Customer Category Identifier";
$table->bigInteger('industry_id')->unsigned()->nullable()->comment="Industry Identifier";
$table->string('email')->unique()->comment="Customer Email";
$table->timestamps();
$table->foreign('industry_id')->references('id')->on('industries');
$table->foreign('customer_category_id')->references('id')->on('customer_categories');
});
}
/**
* Reverse the migrations.
*
* @return void
*/
public function down()
{
Schema::dropIfExists('customers');
}
}
Here is industries migration. 这是行业迁移。
<?php
use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;
class CreateIndustriesTable extends Migration
{
/**
* Run the migrations.
*
* @return void
*/
public function up()
{
Schema::create('industries', function (Blueprint $table) {
$table->bigIncrements('id')->comment="Industry Indetifier";
$table->string('name')->comment="Industry Name";
$table->boolean('status')->default(true)->comment="Active or Inactive";
$table->timestamps();
});
}
/**
* Reverse the migrations.
*
* @return void
*/
public function down()
{
Schema::dropIfExists('industries');
}
}
Is it impossible to achieve what I want ? 实现我想要的是不可能的? or it is just illogical ?
或者它只是不合逻辑? If I am able to add foreign key then I can take various advantages of using foreign key.
如果我能够添加外键,那么我可以利用外键的各种优点。
将行业表中的id(primary_key)更改为唯一键,然后尝试
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