在 Javascript Array 映射中使用 promise 函数
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Using promise function inside Javascript Array map
提问by Jorge
Having an array of objects [obj1, obj2]
有一个对象数组 [obj1, obj2]
I want to use Map function to make a DB query (that uses promises) about all of them and attach the results of the query to each object.
我想使用 Map 函数对所有对象进行数据库查询（使用承诺）并将查询结果附加到每个对象。
[obj1, obj2].map(function(obj){
db.query('obj1.id').then(function(results){
obj1.rows = results
return obj1
})
})
Of course this doesn't work and the output array is [undefined, undefined]
当然这不起作用，输出数组是 [undefined, undefined]
What's the best way of solving a problem like this? I don't mind using other libraries like async
解决此类问题的最佳方法是什么？我不介意使用其他库，比如 async
回答by madox2
Map your array to promises and then you can use Promise.all()function:
将您的数组映射到承诺，然后您可以使用Promise.all()函数：
var promises = [obj1, obj2].map(function(obj){
return db.query('obj1.id').then(function(results){
obj1.rows = results
return obj1
})
})
Promise.all(promises).then(function(results) {
console.log(results)
})
回答by mdziekon
You are not returning your Promises inside the mapfunction.
你没有在map函数内返回你的承诺。
[obj1, obj2].map(function(obj){
return db.query('obj1.id').then(function(results){
obj1.rows = results
return obj1
})
})
