with migration to fill slug with default value - postgresql

Question

In my Laravel 5.6/PostgreSQL 10.5 application
I have 2 tables :
CREATE TABLE public.rt_genres (
id serial NOT NULL,
published bool NULL DEFAULT false,
created_at timestamp NOT NULL DEFAULT now(),
updated_at timestamp NULL,
CONSTRAINT rt_genres_pkey PRIMARY KEY (id)
)...
CREATE TABLE public.rt_genre_translations (
id serial NOT NULL,
genre_id int4 NOT NULL,
"name" varchar(100) NOT NULL,
description text NOT NULL,
created_at timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
locale varchar(2) NOT NULL,
CONSTRAINT genre_translations_genre_id_locale_unique UNIQUE (genre_id, locale),
CONSTRAINT rt_genre_translations_pkey PRIMARY KEY (id),
CONSTRAINT genre_translations_genre_id_foreign FOREIGN KEY (genre_id) REFERENCES rt_genres(id) ON DELETE CASCADE
)
I need to add slug field in first rt_genres table
with migration rule:
$table->string('slug', 105)->unique();
and got error :
: Unique violation: 7 ERROR: could not create unique index "genres_slug_unique"
DETAIL: Key (slug)=(id) is duplicated.")
1)If there is a way to assign in migration some unique default value, like = id
->default('rt_genres.id')
?
2) That would be cool to assign to slug value from public.rt_genre_translations.name as I use
"cviebrock/eloquent-sluggable": "^4.5" plugin in my app ? Can I do it ?
Thank you!

Answer 1

You can only get the default value from a different column with a trigger (SO answer).
You can make the column nullable:
$table->string('slug', 105)->nullable()->unique();
Or you create the column, insert unique values and then create the index:
Schema::table('rt_genres', function($table) {
$table->string('slug', 105);
});
DB::table('rt_genres')->update(['slug' => DB::raw('"id"')]);
Schema::table('rt_genres', function($table) {
$table->unique('slug');
});