Polymorphic Metadata Relationships in Laravel

2016_09_20_112502_create_meta_datas_table.php

<?php

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateMetaDatasTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('metadata', function (Blueprint $table) {
            $table->increments('id');
            $table->string('key');
            $table->text('value')->nullable();
            $table->integer('metable_id')->unsigned();
            $table->string('metable_type');
            $table->timestamps();

            $table->unique(['key','metable_id','metable_type']);
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::drop('metadata');
    }
}

CanHaveMetadataTrait.php

trait CanHaveMetadata
{


    /**
     * Get All Metadata using Polymorphic Relationship
     * @return mixed
     */
    public function metadata()
    {
        return $this->morphMany(MetaData::class, 'metable');
    }


    /**
     * Check if a metadata key already exist.
     * @param $key
     * @return bool
     */
    public function hasMetadata($key)
    {
        return (boolean) $this->metadata()->whereKey($key)->count();
    }

    /**
     * Retrieve a metadata of a Metadata.
     * @param $key
     * @return mixed
     */
    public function getMetadata($key)
    {
        return $this->metadata()->whereKey($key)->first()->value;
    }

    /**
     * Save or update metadata of a Model.
     * @param $key
     * @param $value
     * @return mixed
     */
    public function saveMetadata($key, $value)
    {
        $metadata = $this->metadata()->whereKey($key)->first() ?: new MetaData(['key' => $key]);

        $metadata->value = $value;

        return $this->metadata()->save($metadata);

    }
}

MetaData.php

use Illuminate\Database\Eloquent\Model;

class MetaData extends Model
{
    //

    protected  $table = 'metadata';

    protected $fillable = ['key','value'];

    public function metable()
    {
        return $this->morphTo();

    }

    public function setValueAttribute($value)
    {
        if(is_array($value)){
            $this->attributes['value'] = json_encode($value);
            return ;
        }

        $this->attributes['value'] = $value;

    }

    public function getValueAttribute($value)
    {
        $decodeValue = json_decode($value,true);

        if(is_array($decodeValue)){
            return $decodeValue;
        }

        return $value;

    }
}