order of constraint() method in declaring a foreign key

hello, i faced a little issue where the row couldn't get deleted, i know it seems beginner likely, but i want to understand the issue behind it, and why the order of the methods is important when we declare a foreign key in a migration the correct way based on the documentation:

$table->foreignId('user_id')
     		   ->constrained() // 2nd 
      		   ->onUpdate('cascade')
      		   ->onDelete('cascade');

How to trigger the mistake:

$table->foreignId('user_id')
     		   ->onUpdate('cascade')
      		   ->onDelete('cascade');
 			   ->constrained() // last

so my question is why the constrained order is critical, because if i create a many to many relationship with the user for example, when i delete the user, the rest won't cascade. thank you in advance

Sinnbeck

4 years ago

Level 102

Try running both versions with pretend mode, to see the query

php artisan migrate --pretend

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Tray2

4 years ago

Level 73

My guess is that the first version generates DDL that look somthing like this

CREATE TABLE records( 
  id int auto_increment primary key,
  user_id int,
  FOREIGN KEY (user_id)
      REFERENCES users (id)
      ON DELETE CASCADE
);

While the other way around it tries to add cascade to something that is not defined yet.

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