可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试):

问题:

I get this error when I do php artisan migrate. Is there something wrong in my migration files? Or is it possible my models are wrong coded? But the migrations should work even there is something wrong in the models?

[Exception]                                                                  
  SQLSTATE[HY000]: General error: 1005 Can't create table 'festival_aid.#sql-  
  16643_2033' (errno: 150) (SQL: alter table `gigs` add constraint gigs_band_  
  id_foreign foreign key (`band_id`) references `bands` (`band_id`) on delete  
   cascade) (Bindings: array (                                                 
  ))

[PDOException]                                                               
  SQLSTATE[HY000]: General error: 1005 Can't create table 'festival_aid.#sql-  
  16643_2033' (errno: 150)

gigs migration

public function up()
    {
        Schema::create('gigs', function($table)
        {
            $table->increments('gig_id');

            $table->dateTime('gig_startdate');

            $table->integer('band_id')->unsigned();
            $table->integer('stage_id')->unsigned();

            $table->foreign('band_id')
                ->references('band_id')->on('bands')
                ->onDelete('cascade');

            $table->foreign('stage_id')
                ->references('stage_id')->on('stages')
                ->onDelete('cascade');
        });

    public function down()
    {
        Schema::table('gigs', function($table)
        {
            Schema::drop('gigs');
            $table->dropForeign('gigs_band_id_foreign');
            $table->dropForeign('gigs_stage_id_foreign');
        });
    }

bands migration

public function up()
    {
        Schema::create('bands', function($table)
        {
            $table->increments('band_id');

            $table->string('band_name');
            $table->text('band_members');
            $table->string('band_genre');
            $table->dateTime('band_startdate');
        });
    }

    public function down()
    {
        Schema::table('bands', function(Blueprint $table)
        {
            Schema::drop('bands');
        });
    }

Model Band

<?php

class Band extends Eloquent {

    protected $primaryKey = 'band_id';

    public function gig()
    {
        return $this->hasOne('Gig', 'band_id', 'band_id');
    }
}

Model Gig

<?php

class Gig extends Eloquent {
    protected $primaryKey = 'gig_id';

    public function gig()
    {
        return $this->belongsTo('Band', 'band_id', 'band_id');
    }

    public function stage()
    {
        return $this->belongsTo('Stage', 'stage_id', 'stage_id');
    }
}

回答1:

You must first create the table, then create the foreign keys:

Schema::create('gigs', function($table)
{
    $table->increments('gig_id');

    $table->dateTime('gig_startdate');

    $table->integer('band_id')->unsigned();
    $table->integer('stage_id')->unsigned();
});

Schema::table('gigs', function($table)
{
    $table->foreign('band_id')
        ->references('band_id')->on('bands')
        ->onDelete('cascade');

    $table->foreign('stage_id')
        ->references('stage_id')->on('stages')
        ->onDelete('cascade');
});

And your bands table should migrate first, since the gigs is referencing it.

回答2:

While this doesn't apply to OP, others might have this issue:

From the bottom of the Laravel Schema docs:

Note: When creating a foreign key that references an incrementing integer, remember to always make the foreign key column unsigned.

You can do this via $table->integer('user_id')->unsigned(); when creating your table in the migration file.

Took me a few minutes to realize what was happening.

回答3:

For those whom other answers doesn't help, the same error throws also when you try to use 'SET_NULL' action on non-nullable column.

回答4:

As said by Andrew by making the reference on the table as this:

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

It should work.

回答5:

for those who are still having this issue, make sure the field you setting as foreign key is a primary key or should be unique since a foreign key can only be a primary or unique field. see sample below

Schema::create('users', function (Blueprint $table) {
  $table->increments('id');
  $table->string('username',25)->unique();
 });

Schema::create('another_table', function (Blueprint $table) {
   $table->increments('id');
   $table->string('name', 25);
   $table->foreign('name')->references('username')->on('users')
 });

回答6:

        $table->integer('band_id')->unsigned();
        $table->integer('stage_id')->unsigned();

In laravel 5.8, the users_table uses bigIncrements('id') data type for the primary key. So that when you want to refer a foreign key constraint your band_id,stage_id column needs to be unsignedBigInteger('stage_id') and band_id type.

The manager also tested this way.

回答7:

This seems to be a general foreign key issue error. For me I got it when I switched the arguments in the references and on methods. I had:

$table->foreign('user_id')->references('users')->on('id');

instead of:

$table->foreign('user_id')->references('id')->on('users');

回答8:

I just fixed this problem by making pointing to Laravel that the field is unique using unique().

Example:

Schema::create('branches', function (Blueprint $table) {
            $table->increments('id');
            /* This fields serves as foriegn key on functions 
            table and it must follow the database **key rules**
            by being unique */
            $table->string('branch_code')->unique();
            $table->string('branch_name');
            $table->string('branch_address');
            $table->timestamps();
        });

Functions table:

    Schema::create('functions', function (Blueprint $table) {
        $table->increments('id');
        $table->string('branch_code');
        $table->string('function');
        $table->timestamps();
        //Reference to branch_code on branches table
        $table->foreign('branch_code')->references('branch_code')->on('branches');

    });