将undefined转换为map 时出错

Question

我试图用mobx-state-tree创建一个超级简单的嵌套存储，我无法弄清楚如何让它工作。要么这个图书馆非常不直观，要么我错过了一些显而易见的东西。我尝试在MST.types.optional()中包装所有内容，看看这是否有所作为，但不是。将undefined转换为map <string，AnonymousModel>时出错

这个想法是，订单商店有很多买卖订单。我想创建一个没有任何订单的空商店。

当我尝试执行Orders.js，我得到以下错误：

Error: [mobx-state-tree] Error while converting `undefined` to `map<string, AnonymousModel>`: value `undefined` is not assignable to type: `map<string, AnonymousModel>` (Value is not a plain object), expected an instance of `map<string, AnonymousModel>` or a snapshot like `Map<string, { timestamp: Date; amount: number; price: number }>` instead.` 

order.js

const MST = require("mobx-state-tree") 

const Order = MST.types.model({ 
    timestamp: MST.types.Date, 
    amount: MST.types.number, 
    price: MST.types.number, 
}).actions(self => { 
    function add(timestamp, price, amount) { 
     self.timestamp = timestamp 
     self.price = price 
     self.amount = amount 
    } 
    return { add } 
}) 

module.exports = Order 

orders.js

const MST = require("mobx-state-tree") 
const Order = require('./order') 

const Orders = MST.types.model({ 
    buys: MST.types.map(Order), 
    sells: MST.types.map(Order), 
}).actions(self => { 
    function addOrder(type, timestamp, price, amount) { 
     if(type === 'buy'){ 
      self.buys.add(timestamp, price, amount) 
     } else if(type === 'sell') { 
      self.sells.add(timestamp, price, amount) 
     } else throw Error('bad order type') 
    } 
    return { addOrder } 
}) 
Orders.create() 

Answer 1

是的，你需要把所有东西都包裹起来types.optional并为其提供默认快照。 下面是一个例子

const MST = require("mobx-state-tree") 
const Order = require('./order') 

const Orders = MST.types.model({ 
    buys: MST.types.optional(MST.types.map(Order), {}), 
    sells: MST.types.optional(MST.types.map(Order), {}), 
}).actions(self => { 
    function addOrder(type, timestamp, price, amount) { 
     if(type === 'buy'){ 
      self.buys.add(timestamp, price, amount) 
     } else if(type === 'sell') { 
      self.sells.add(timestamp, price, amount) 
     } else throw Error('bad order type') 
    } 
    return { addOrder } 
}) 
Orders.create() 

幕后types.optional做的是拦截未定义，替换成你的默认值:)