A crazy database structure - suggestions - mysql

Question

I'm working on a project where I need to create three Many-to-Many relationships between 4 models. Here is how it goes:
FAQ Categories can have many FAQ Subcategories and vice versa.
FAQ Groups can have many FAQ Subcategories and vice versa.
FAQs can have many FAQ groups and vice versa.
To all the database experts out there, how should I design this database schema in Laravel? Should I have three different pivot tables? Should I use polymorphic relationships?
I've used polymorphic relationships before, but I'm struggling with implementing it in this scenario.

Answer 1

I would do something like this:
FAQ Categories Table
Schema::create('faq_categories', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
});
Schema::table('faq_categories', function (Blueprint $table) {
$table->unsignedInteger('parent_id')->nullable();
$table->foreign('parent_id')->references('id')->on('faq_categories')->onDelete('cascade');
});
FAQ Groups Table
Schema::create('faq_groups', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
});
FAQs Table
Schema::create('faqs', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
});
As you can see I wouldn't create a FAQ Sub Categories table, because it's cleaner to have a category table referencing itself to a parent category (also important to make that foreign key nullable to be able to create a top level category).
Now to setup the relationships between the tables, we can do this:
FAQ Categories - FAQ Groups (Many to Many)
Schema::create('faq_category_faq_group', function (Blueprint $table) {
$table->increments('id');
$table->unsignedInteger('faq_category_id');
$table->foreign('faq_category_id')->refrences('id')->on('faq_categories')->onDelete('cascade');
$table->unsignedInteger('faq_group_id');
$table->foreign('faq_group_id')->refrences('id')->on('faq_groups')->onDelete('cascade');
});
FAQs - FAQ Groups (Many to Many)
Schema::create('faq_faq_group', function (Blueprint $table) {
$table->increments('id');
$table->unsignedInteger('faq_id');
$table->foreign('faq_id')->refrences('id')->on('faqs')->onDelete('cascade');
$table->unsignedInteger('faq_group_id');
$table->foreign('faq_group_id')->refrences('id')->on('faq_groups')->onDelete('cascade');
});
Should I use polymorphic relationships?
I don't think polymorphic relationship's would make any sense in this scenario. I would stick with standard many to many.
In your model classes you should setup all the relationships like referenced in the docs.
You can do this:
FaqCategory Model
class FaqCategory extends Model
{
/**
* Get the category's parent category.
*/
public function parent()
{
return $this->belongsTo('App\FaqCategory');
}
/**
* Get the category's sub categories.
*/
public function sub_categories()
{
return $this->hasMany('App\FaqCategory', 'parent_id');
}
/**
* Get the category's faq groups.
*/
public function faq_groups()
{
return $this->belongsToMany('App\FaqGroup');
}
}
FaqGroup Model
class FaqGroup extends Model
{
/**
* Get the group's faq categories.
*/
public function faq_categories()
{
return $this->belongsToMany('App\FaqCategory');
}
/**
* Get the group's faqs.
*/
public function faqs()
{
return $this->belongsToMany('App\Faq');
}
}
Faq Model
class Faq extends Model
{
/**
* Get the faq's faq groups.
*/
public function faq_groups()
{
return $this->belongsToMany('App\FaqGroup');
}
}

Answer 2

One concern is whether FAQ Categories and Subcategories should be different tables. Maybe should be the same table in order to give you the option to have more levels in the future.
i.e.
faq_categories(id, parent_id, name etc.)
Then, in my opinion, you need just different pivot tables. I can not see any reason to use polymorphic relationships.