php - Eloquent Attach() 处理非对象错误

Question

我正在尝试将消息附加到对话(多对多)，但出现错误。我错过了什么？

数据透视表架构

conversation_message (conversation_id, message_id)

模型

class Conversation extends Eloquent
{
    public function messages()
    {
        $this->belongsToMany('Message', 'conversation_message', 'conversation_id', 'message_id');
    }
}

class Message extends Eloquent
{
    public function conversations()
    {
        $this->belongsToMany('Conversation', 'conversation_message', 'message_id', 'conversation_id');
    }
}

Controller

$conversation = Conversation::find(1);
$message = Message::find(1);
$conversation->messages()->attach($message);

错误

Call to a member function attach() on a non-object

Answer 1

两种方法都缺少return:

class Conversation extends Eloquent
{
    public function messages()
    {
        return $this->belongsToMany('Message', 'conversation_message', 'conversation_id', 'message_id');
    }
}

class Message extends Eloquent
{
    public function conversations()
    {
        return $this->belongsToMany('Conversation', 'conversation_message', 'message_id', 'conversation_id');
    }
}