英文:
How to nested map for res.json() in express
问题
我正在开发一个提供电影信息给用户的 Express 应用程序（服务器端），但我试图发送一个 JSON 响应，格式如下：...
问题是我似乎无法将主要信息数据输出，而是会返回 {}，如下：...
外部的对象，如 title, year, runtime, genres, 等，都在一个叫做 basics 的表中，而 principals 中的每个对象都在另一个叫做 principals 的表中。
到目前为止，我已经完成了以下工作：...
英文:
I am working on an express application (server-side) that provides movie information to users but I am trying to send a JSON response like this:
{
"title": "Star Trek: First Contact",
"year": 1996,
"runtime": 111,
"genres": [
"Action",
"Adventure",
"Drama"
],
"country": "United States",
"principals": [
{
"id": "nm0005772",
"category": "cinematographer",
"name": "Matthew F. Leonetti",
"characters": []
},
{
"id": "nm0001772",
"category": "actor",
"name": "Patrick Stewart",
"characters": [
"Picard"
]
},
{
"id": "nm0000408",
"category": "actor",
"name": "Jonathan Frakes",
"characters": [
"Riker"
]
},
{
"id": "nm0000653",
"category": "actor",
"name": "Brent Spiner",
"characters": [
"Data"
]
},
{
"id": "nm0000996",
"category": "actor",
"name": "LeVar Burton",
"characters": [
"Geordi"
]
},
{
"id": "nm0734472",
"category": "writer",
"name": "Gene Roddenberry",
"characters": []
},
{
"id": "nm0075834",
"category": "writer",
"name": "Rick Berman",
"characters": []
},
{
"id": "nm0103804",
"category": "writer",
"name": "Brannon Braga",
"characters": []
},
{
"id": "nm0601822",
"category": "writer",
"name": "Ronald D. Moore",
"characters": []
},
{
"id": "nm0000025",
"category": "composer",
"name": "Jerry Goldsmith",
"characters": []
}
],
"boxoffice": 92027888,
"poster": "https://m.media-amazon.com/images/M/MV5BYzMzZmE3MTItODYzYy00YWI5LWFkNWMtZTY5NmU2MDkxYWI1XkEyXkFqcGdeQXVyMjUzOTY1NTc@._V1_SX300.jpg",
"plot": "The Borg travel back in time intent on preventing Earth's first contact with an alien species. Captain Picard and his crew pursue them to ensure that Zefram Cochrane makes his maiden flight reaching warp speed."
}
The problem is that I can't seem to get the principals data to output as it would return {} instead:
{
"title": "Star Trek: First Contact",
"year": 1996,
"runtime": 111,
"genres": [
"Action",
"Adventure",
"Drama"
],
"country": "United States",
"principals": {},
"boxoffice": 92027888,
"poster": "https://m.media-amazon.com/images/M/MV5BYzMzZmE3MTItODYzYy00YWI5LWFkNWMtZTY5NmU2MDkxYWI1XkEyXkFqcGdeQXVyMjUzOTY1NTc@._V1_SX300.jpg",
"plot": "The Borg travel back in time intent on preventing Earth's first contact with an alien species. Captain Picard and his crew pursue them to ensure that Zefram Cochrane makes his maiden flight reaching warp speed."
}
The objects outside such as title, year, runtime, genres, etc. are all in a table called basics, meanwhile every object inside principals are in another table called principals.
Here is what I've done so far:
router.get('/movies/data/:imdbID', function(req, res, next) {
const queryMovie = req.db.from('basics').select(
'primaryTitle',
'year',
'runtimeMinutes',
'genres',
'country',
'boxoffice',
'poster',
'plot'
).where('tconst', req.params.imdbID)
const queryPrincipals = req.db.from('principals').select('nconst', 'category', 'name', 'characters').where('tconst', req.params.imdbID)
queryMovie.then((movieData) => {
const movie = movieData.map(data => {
return {
title: data.tconst,
year: data.year,
runtime: data.runtimeMinutes,
country: data.country,
principals: queryPrincipals.then((principals) => {
principals.map(principal => {
return {
id: principal.nconst,
category: principal.category,
name: principal.name,
characters: principal.characters
}
})
}),
boxoffice: data.genres,
poster: data.genres,
plot: data.plot
}
})
res.json(movie)
})
});
答案1
得分: 1
你正在在一个异步函数中构建你的 principals 对象。这意味着返回对象的 return 语句在异步函数返回之前运行，所以你得到的是一个空对象，而不是实际数据。
请使用 async/await 来确保在返回之前数据可用。
router.get('/movies/data/:imdbID', async function(req, res, next) {
const queryMovie = req.db.from('basics')
.select(
'primaryTitle',
'year',
'runtimeMinutes',
'genres',
'country',
'boxoffice',
'poster',
'plot'
)
.where('tconst', req.params.imdbID)
const queryPrincipals = req.db.from('principals')
.select('nconst', 'category', 'name', 'characters')
.where('tconst', req.params.imdbID)
const movieData = await queryMovie();
const movie = movieData.map(({ tconst:title, year, runtimeMinutes:runtime, country, genres, plot }) => {
const principals = await queryPrincipals().map(
({nconst:id, category, name, characters}) => ({ id, category, name, characters })
);
return {
title,
year,
runtime,
country,
principals,
boxoffice: genres,
poster: genres,
plot
}
})
res.json(movie)
});
希望这能帮助你解决问题。
英文:
You are building your principals object in an async function. This means that the return statement that returns the object is running before the async function returns and you're getting an empty object instead of actual data.
Use async/await to ensure that your data is available before the return.
router.get('/movies/data/:imdbID', async function(req, res, next) {
const queryMovie = req.db.from('basics')
.select(
'primaryTitle',
'year',
'runtimeMinutes',
'genres',
'country',
'boxoffice',
'poster',
'plot'
)
.where('tconst', req.params.imdbID)
const queryPrincipals = req.db.from('principals')
.select('nconst', 'category', 'name', 'characters')
.where('tconst', req.params.imdbID)
const movieData = await queryMovie();
const movie = movieData.map(({ tconst:title, year, runtimeMinutes:runtime, country, genres, plot }) => {
const principals = await queryPrincipals().map(
({nconst:id, category, name, characters}) => ({ id, category, name, characters })
);
return {
title,
year,
runtime,
country,
principals,
boxoffice: genres,
poster: genres,
plot
}
})
res.json(movie)
})
});
</details>
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