將undefined轉換爲map <string，AnonymousModel>時出錯

Question

我試圖用mobx-state-tree創建一個超級簡單的嵌套存儲，我無法弄清楚如何讓它工作。要麼這個圖書館非常不直觀，要麼我錯過了一些顯而易見的東西。我嘗試在MST.types.optional()中包裝所有內容，看看這是否有所作爲，但不是。

這個想法是，訂單商店有很多買賣訂單。我想創建一個沒有任何訂單的空商店。

當我嘗試執行Orders.js，我得到以下錯誤：

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，你需要把所有東西都包裹起來types.optional併爲其提供默認快照。 下面是一個例子

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() 

幕後types.optional做的是攔截未定義，替換成你的默認值:)