private static function createCategoryRelationsTable($postTypeSlug)
    {
        if(!Schema::hasTable($postTypeSlug."_categories")) {
            Schema::create(
                $postTypeSlug."_categories", function ($table) use ($postTypeSlug) {
                    // create general fields
                    $table->bigIncrements("categoryRelationID");
                    $table->bigInteger("postID")->unsigned()->nullable();
                    $table->unsignedInteger("categoryID")->nullable();

                    $table->foreign('postID')
                        ->references('postID')->on($postTypeSlug)
                        ->onDelete('cascade');

                    $table->foreign('categoryID')
                        ->references('categoryID')->on("categories")
                        ->onDelete('cascade');

                    $table->unique(array('postID', 'categoryID'));
                }
            );
        }
    }