add keywords during publishing

app/Models/Subject.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use App\Models\Dataset;
+
+class Subject extends Model
+{
+    protected $table = 'document_subjects';
+    public $timestamps = false;
+
+    protected $fillable = ['value', 'type'];
+
+    public function dataset()
+    {
+        return $this->belongsTo(Dataset::class, 'document_id', 'id');
+    }
+}