如何在javascript中运行异步inside.map?
我有一个数据库选择函数,我希望在其中具有以下输出格式:如何在javascript中运行异步inside.map?,javascript,node.js,data-modeling,Javascript,Node.js,Data Modeling,我有一个数据库选择函数,我希望在其中具有以下输出格式: { "recipe_id" : 1, "recipe_name": "Spaghetti Bolognese", "created_at": "2021-01-01 08:23:19.120", "steps": [ { "step_id": 11, &q
{
"recipe_id" : 1,
"recipe_name": "Spaghetti Bolognese",
"created_at": "2021-01-01 08:23:19.120",
"steps": [
{
"step_id": 11,
"step_number": 1,
"step_instructions": "Put a large saucepan on a medium heat",
"ingredients": []
},
{
"step_id": 12,
"step_number": 2,
"step_instructions": "Add 1 tbsp olive oil",
"ingredients": [
{ "ingredient_id": 27, "ingredient_name": "olive oil", "quantity": 0.014 }
]
},
]
}
我创建了以下数据库函数来执行步骤部分:
const getIngredientsStepById = async (step_id) =>{
const data = await db('step_ingredient_info as sii')
.join('steps', 'steps.step_id', 'sii.step_id')
.join('ingredients', 'ingredients.ingredient_id', 'sii.ingredient_id')
.where('steps.step_id', step_id)
let returnObj = data[0]? data.map(ingredient => {
return {
ingredient_id: ingredient.ingredient_id,
ingredient_name: ingredient.ingredient_name,
quantity: ingredient.quantity
}
}) : []
return returnObj
}
它提供以下输出
[
{
"ingredient_id": 1,
"ingredient_name": "egg",
"quantity": "2 eggs"
},
{
"ingredient_id": 2,
"ingredient_name": "salt",
"quantity": "a pinch of salt"
}
]
我试图将其与当前代码结合起来:
const getRecipeById = async recipe_id => {
let data = await db('recipes as r')
.join('steps as st', 'st.recipe_id', 'r.recipe_id')
.where('r.recipe_id', recipe_id)
.orderBy('st.step_number')
let recipeObj = {
recipe_name: data[0].recipe_name,
steps:
data[0].step_id ? data.map(step =>{
return {
step_id: step.step_id,
step_number: step.step_number,
instructions: step.step_instructions
}
}) : []
};
return recipeObj
}
它目前有这个输出,这是好的:
{
"recipe_name": "fried egg",
"steps": [
{
"step_id": 1,
"step_number": 1,
"instructions": "add oil and heat pan"
},
{
"step_id": 2,
"step_number": 2,
"instructions": "crack egg into pan in medium heat for 2-3 mins and sprinkle salt"
},
{
"step_id": 3,
"step_number": 3,
"instructions": "serve"
}
]
}
但现在,我尝试使用async获取成分,以便在步骤中添加成分数组,代码在其中停止工作,它显示在控制台中,但没有得到输出
使用async的代码是:
const getRecipeById = async recipe_id => {
let data = await db('recipes as r')
.join('steps as st', 'st.recipe_id', 'r.recipe_id')
.where('r.recipe_id', recipe_id)
.orderBy('st.step_number')
let recipeObj = {
recipe_name: data[0].recipe_name,
steps:
data[0].step_id ? data.map(async step =>{
let ingredients = await getIngredientsStepById(step.step_id);
console.log(ingredients);
return {
step_id: step.step_id,
step_number: step.step_number,
instructions: step.step_instructions,
ingredients: ingredients
}
}) : []
};
return recipeObj
}
map
,forEach
,reduce
等,async
将无效
但是看看你的代码,你可以把第二阶段变成一个简单的
const getRecipeById = async recipe_id => {
let data = await db('recipes as r')
.join('steps as st', 'st.recipe_id', 'r.recipe_id')
.where('r.recipe_id', recipe_id)
.orderBy('st.step_number')
let recipeObj = {
recipe_name: data[0].recipe_name,
steps:
data[0].step_id ? data.map(step =>{
return {
step_id: step.step_id,
step_number: step.step_number,
instructions: step.step_instructions,
}
}) : []
};
for (const step of recipeObj.steps) {
step.ingredients = await getIngredientsStepById(step.step_id);
}
return recipeObj
}
这回答了你的问题吗?
async
函数返回一个承诺,因此map()
生成一个承诺数组。你需要调用Promise。所有的都会等待结果。你的map
调用中仍然有一个async
函数,正如Bergi指出的那样,删除了map调用中的async,但剩下的都是天赐的。非常感谢。我甚至没想过要走这条路。@Bergi干杯,好的老拷贝粘贴…)