Laravel 5 如何在保存时验证每个活动下的唯一客户名称

我有三个模型：活动模型、客户模型和客户项目模型

如何在商店功能中进行验证检查，使每个活动中的客户名称应该是唯一的？

以下是每个迁移文件

活动模型

public function up()
{
    Schema::create('activities', function (Blueprint $table) {
        $table->increments('id');
        $table->string('activityName');
        $table->string('activityCode');
        $table->string('activityVenue');
        $table->timestamps();
    });
}

客户模型

public function up()
{
    Schema::create('customers', function (Blueprint $table) {
        $table->increments('id');
        $table->integer('activities_id')->unsigned()->default(0);
        $table->foreign('activities_id')->references('id')->on('activities')->onDelete('cascade');
        $table->text('remark')->nullable();
        $table->timestamps();
    });
}

客户项目模型

public function up()
{
    Schema::create('customeritems', function (Blueprint $table) {
        $table->increments('id');
        $table->integer('customers_id')->unsigned()->default(0);
        $table->foreign('customers_id')->references('id')->on('customers')->onDelete('cascade');
        $table->string('customerName');
        $table->integer('customerAge')->unsigned();
        $table->timestamps();
    });
}

存储新条目的控制器

public function store(Request $request)
{
    $rules = array(
        'customerName' => 'required|distinct',         
    );
    $messages = array(
        'customerName.required'=>'Customer Name is required',
        'customerName.distinct'=>'Customer Name has a duplicate value.',
    );

这里如何对每个活动的唯一 customerName 进行验证？