Laravel - 在现有表上添加外键和数据

Laravel - add foreign key on existing table with data(Laravel - 在现有表上添加外键和数据)

问题描述

我有现有的表 objects 与数据.现在我需要添加名为 holdings 的新表，并将对象之间的关系添加到 holdings 表.在迁移文件中，我打印了这个:

I have existing table objects with data. Now I need to add new table named holdings and add a relation from objects to holdings table. In the migration file, I print this:

$table->foreign('holding_id')->references('id')->on('holdings')->onDelete("NO ACTION");

并在尝试迁移时收到此错误

and get this error when trying to migrate

SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update 
a child row: a foreign key constraint fails (`kolomnaoffice`.`#sql-f10_126` 
CONSTRAINT `objects_holding_id_foreign` FOREIGN KEY (`holding_id`) 
REFERENCES `holdings` (`id`) ON DELETE NO ACTION) (SQL: alter table `objects` add constraint 
`objects_holding_id_foreign` foreign key (`holding_id`) references `holdings` 
(`id`) on delete NO ACTION)

我有正确的数据库结构(两个 InnoDB)，字段存在并且具有正确的类型(int).唯一不同的是，objects 表是数据，而holdings 表是新的空的.

I have correct database structure (both InnoDB), the fields exist and have correct type (int). The only thing different is that the table objects is filled with data, and table holdings is new and empty.

推荐答案

holding_id列应该是unsigned

新建一个迁移文件并迁移，迁移代码应该是这样的:

Create a new migration file and migrate it, migration code should be like this :

Schema::table('objects', function (Blueprint $table) {
    $table->integer('holding_id')->unsigned()->change();

    $table->foreign('holding_id')->references('id')->on('holdings');
});

调用change()方法改变现有列的结构.

The change() method is called to change the structure of existing column.

不需要调用onDelete("NO ACTION")方法.

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