How to migrate from string column to foreign key pointing to row in other table with same string value in Laravel? - sql

Question

I am using Laravel 5.6 and need some help migrating a column from a populated table preserving the content logic. There is a table pages with a column named icon that accepts string values.
Ex:
Schema::create('pages', function (Blueprint $table) {
$table->increments('id');
...
$table->string('icon')->nullable();
}
The pages table is populated and the icon column, being nullable, is not always used.
A new icons table was created to store all the usable icon classes.
Ex:
Schema::create('icons', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
});
How can i migrate the icon column from the pages table to be a foreign key that points to the icons table row that has the same value in the name column or null if not populated?

Answer 1

I'd suggest a polymorphic many-to-many approach here so that icons are reusable and don't require a bunch of pivot tables, should you want icons on something other than a page.
Schema::create('icons', function(Blueprint $table) {
$table->increments('id');
$table->string('name');
});
Schema::create('iconables', function(Blueprint $table) {
$table->integer('icon_id');
$table->integer('iconables_id');
$table->integer('iconables_type');
});
Now you just need to determine if the pages have an existing Icon. If they do, then hold reference to them so you can insert them:
$pagesWithIcons = Page::whereNotNull('icon')->get();
At this point you need to define the polymorphic relations in your models:
// icon
class Icon extends Model
{
public function pages()
{
return $this->morphedByMany(Page::class, 'iconable');
}
}
// page
class Page extends Model
{
public function pages()
{
return $this->morphToMany(Icon::class, 'iconable');
}
}
Now you just need to create the icons (back in our migration), and then attach them if they exist:
$pagesWithIcons->each(function(Page $page) {
$icon = Icon::firstOrNew([
'name' => $page->icon
});
$icon->pages()->attach($page);
});
The above is creating an Icon if it doesn't exist, or querying for it if it does. Then it's attaching the page to that icon. As polymorphic many-to-many relationships just use belongsToMany() methods under the hood, you have all of the available operations at your leisure if this doesn't suite your needs.
Finally, drop your icons column from pages, you don't need it.
Schema::table('pages', function(Blueprint $table) {
$table->dropColumn('icon');
});
And if you need to backfill support for only an individual icon (as the many-to-many will now return an array relationship), you may add the following to your page model:
public function icon()
{
return $this->icons()->first();
}
Apologies if typos, I did this on my phone so there may be some mistakes.