Mongoose重新分配数组属性

Question

我不明白为什么无法重新分配Mongoose find结果引用。

例如

Ticket.findOne({_id: req.params.id}, (err, ticket) => {
    console.log("before: ", ticket)
    ticket.tasks = [1, 2] //won't work
    ticket.title = "foo"
    console.log("after: ", ticket)
    console.log("=========")
    let copyTicket = ticket.toObject()
    console.log("Solution after: ", copyTicket)
    copyTicket.tasks = [1, 2]
    copyTicket.title = "bar"
    console.log("Solution before: ", copyTicket)
})

输出

before:  { tasks: [],
  _id: 5aa17051e97eac407b72757a,
  title: 'ho'
  }
after:  { tasks: [],
  _id: 5aa17051e97eac407b72757a,
  title: 'foo',
  }
=========
Solution after:  { tasks: [],
  _id: 5aa17051e97eac407b72757a,
  title: 'foo',
  }
Solution before:  { tasks: [ 1, 2 ],
  _id: 5aa17051e97eac407b72757a,
  title: 'bar',
  }

您是否有任何想法如何以及为何会出现这种行为？