.map 函数中的多个查询
Multiple queries in a .map function
const returnPostData = async (req, res, initialPostsQueryArray) => {
try{
const promises = initialPostsQueryArray.map( async (post) => {
let voteCount = 0;
let voted = false;
let liked = false;
let userHandle;
let userImageUrl;
let votingOptionsDictionary;
let userVoteOption;
voteCount = sumValues(post.voting_options);
pool.query('SELECT userhandle, image_url FROM users WHERE id = ',
[post.user_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
const userPostquery = results.rows[0];
userHandle = userPostQuery.userhandle;
userImageUrl = userPostQuery.image_url;
pool.query('SELECT EXISTS( SELECT 1 FROM likes WHERE user_id = AND post_id = )',
[req.user.userId, post.post_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
// if the user like exists, set liked = true
if(results.rows[0].exists == true){
liked = true;
}
pool.query('SELECT EXISTS( SELECT 1 FROM votes WHERE user_id = AND post_id = )',
[req.user.userId, post.post_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
// if the user vote exists, set voted = true and query for what they voted for
if(results.rows[0].exists == true){
voted = true;
votingOptionsDictionary = post.voting_options;
pool.query('SELECT voting_option FROM votes WHERE user_id = AND post_id = ',
[req.user.userId, post.post_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
userVoteOption = results.rows[0].voting_option;
});
}
// i dont need voteCount here because that is calculated after the first query, this gets all the counts of the posts
pool.query('SELECT posts.post_id, ' +
'COALESCE( likes.cnt, 0 ) AS like_count ,' +
'COALESCE( comments.cnt, 0 ) AS comment_count ,' +
'COALESCE( shares.cnt, 0 ) AS share_count ' +
'FROM posts ' +
'LEFT JOIN ( SELECT post_id, COUNT(*) AS cnt FROM likes GROUP BY post_id ) likes ON posts.post_id = likes.post_id ' +
'LEFT JOIN ( SELECT post_id, COUNT(*) AS cnt FROM comments GROUP BY post_id ) comments ON posts.post_id = comments.post_id ' +
'LEFT JOIN ( SELECT post_id, COUNT(*) AS cnt FROM shares GROUP BY post_id ) shares ON posts.post_id = shares.post_id ' +
'WHERE posts.post_id = ',
[post.post_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
const countQuery = results.rows[0];
// final response once all above queries are done, i dont account for thread comments in comment count rn, later problem
return {
postId: post.post_id,
userHandle: userHandle,
userImageUrl: userImageUrl,
postQuestion: post.post_question,
imageUrl: post.post_image_url,
postDescription: post.post_description,
votingOptions: Object.keys(post.voting_options),
voted: voted,
userVoteOption: userVoteOption,
liked: liked,
votingOptionsDictionary: votingOptionsDictionary,
voteStat: voteCount,
likeCount: parseInt(countQuery.like_count),
shareCount: parseInt(countQuery.share_count),
commentCount: parseInt(countQuery.comment_count),
createdAt: post.created_at
};
});
});
});
});
});
const postData = await Promise.all(promises);
return res.json(postData);
}
catch(e){
return res.json(e)
}
}
我正在尝试 return 每个 post 的 post 数据数组。出于某种原因，它继续为这些对象打印 null，因为 return res.json 在承诺完成之前不知何故 运行。感谢任何帮助。
我以前遇到过这个问题并使用了相同的代码，但由于某种原因它对这个不起作用。
您仍然没有使用承诺，但将回调传递给 query。你不能从那些 return，Promise.all 也不会等待它们。您正在寻找
async function returnPostData(req, res, initialPostsQueryArray) {
try{
const promises = initialPostsQueryArray.map( async (post) => {
const voteCount = sumValues(post.voting_options);
const results = await pool.query(
'SELECT userhandle, image_url FROM users WHERE id = ',
[post.user_id],
]);
const userPostquery = results.rows[0];
const userHandle = userPostQuery.userhandle;
const userImageUrl = userPostQuery.image_url;
const {rows: likes } = await pool.query(
'SELECT EXISTS( SELECT 1 FROM likes WHERE user_id = AND post_id = )',
[req.user.userId, post.post_id],
);
// if the user like exists, set liked = true
const liked = likes[0].exists;
const {rows: votes} = await pool.query(
'SELECT EXISTS( SELECT 1 FROM votes WHERE user_id = AND post_id = )',
[req.user.userId, post.post_id]
);
// if the user vote exists, set voted = true and query for what they voted for
const voted = votes[0].exists;
if (voted) {
votingOptionsDictionary = post.voting_options;
const { rows } = await pool.query(
'SELECT voting_option FROM votes WHERE user_id = AND post_id = ',
[req.user.userId, post.post_id]
);
userVoteOption = rows[0].voting_option;
}
// i dont need voteCount here because that is calculated after the first query, this gets all the counts of the posts
const {rows: posts } = await pool.query(
`SELECT
posts.post_id,
COALESCE( likes.cnt, 0 ) AS like_count,
COALESCE( comments.cnt, 0 ) AS comment_count,
COALESCE( shares.cnt, 0 ) AS share_count
FROM posts
LEFT JOIN (
SELECT post_id, COUNT(*) AS cnt
FROM likes
GROUP BY post_id
) likes ON posts.post_id = likes.post_id
LEFT JOIN (
SELECT post_id, COUNT(*) AS cnt
FROM comments
GROUP BY post_id
) comments ON posts.post_id = comments.post_id
LEFT JOIN (
SELECT post_id, COUNT(*) AS cnt
FROM shares
GROUP BY post_id
) shares ON posts.post_id = shares.post_id
WHERE posts.post_id = `,
[post.post_id],
);
const countQuery = posts[0];
// final response once all above queries are done, i dont account for thread comments in comment count rn, later problem
return {
postId: post.post_id,
userHandle: userHandle,
userImageUrl: userImageUrl,
postQuestion: post.post_question,
imageUrl: post.post_image_url,
postDescription: post.post_description,
votingOptions: Object.keys(post.voting_options),
voted: voted,
userVoteOption: userVoteOption,
liked: liked,
votingOptionsDictionary: votingOptionsDictionary,
voteStat: voteCount,
likeCount: parseInt(countQuery.like_count),
shareCount: parseInt(countQuery.share_count),
commentCount: parseInt(countQuery.comment_count),
createdAt: post.created_at
};
});
const postData = await Promise.all(promises);
return res.json(postData);
}
catch(e){
return res.json(e)
}
}
const returnPostData = async (req, res, initialPostsQueryArray) => {
try{
const promises = initialPostsQueryArray.map( async (post) => {
let voteCount = 0;
let voted = false;
let liked = false;
let userHandle;
let userImageUrl;
let votingOptionsDictionary;
let userVoteOption;
voteCount = sumValues(post.voting_options);
pool.query('SELECT userhandle, image_url FROM users WHERE id = ',
[post.user_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
const userPostquery = results.rows[0];
userHandle = userPostQuery.userhandle;
userImageUrl = userPostQuery.image_url;
pool.query('SELECT EXISTS( SELECT 1 FROM likes WHERE user_id = AND post_id = )',
[req.user.userId, post.post_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
// if the user like exists, set liked = true
if(results.rows[0].exists == true){
liked = true;
}
pool.query('SELECT EXISTS( SELECT 1 FROM votes WHERE user_id = AND post_id = )',
[req.user.userId, post.post_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
// if the user vote exists, set voted = true and query for what they voted for
if(results.rows[0].exists == true){
voted = true;
votingOptionsDictionary = post.voting_options;
pool.query('SELECT voting_option FROM votes WHERE user_id = AND post_id = ',
[req.user.userId, post.post_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
userVoteOption = results.rows[0].voting_option;
});
}
// i dont need voteCount here because that is calculated after the first query, this gets all the counts of the posts
pool.query('SELECT posts.post_id, ' +
'COALESCE( likes.cnt, 0 ) AS like_count ,' +
'COALESCE( comments.cnt, 0 ) AS comment_count ,' +
'COALESCE( shares.cnt, 0 ) AS share_count ' +
'FROM posts ' +
'LEFT JOIN ( SELECT post_id, COUNT(*) AS cnt FROM likes GROUP BY post_id ) likes ON posts.post_id = likes.post_id ' +
'LEFT JOIN ( SELECT post_id, COUNT(*) AS cnt FROM comments GROUP BY post_id ) comments ON posts.post_id = comments.post_id ' +
'LEFT JOIN ( SELECT post_id, COUNT(*) AS cnt FROM shares GROUP BY post_id ) shares ON posts.post_id = shares.post_id ' +
'WHERE posts.post_id = ',
[post.post_id],
(error, results) => {
if (error) {
console.log(error);
return res.json({'Error': error.detail});
}
const countQuery = results.rows[0];
// final response once all above queries are done, i dont account for thread comments in comment count rn, later problem
return {
postId: post.post_id,
userHandle: userHandle,
userImageUrl: userImageUrl,
postQuestion: post.post_question,
imageUrl: post.post_image_url,
postDescription: post.post_description,
votingOptions: Object.keys(post.voting_options),
voted: voted,
userVoteOption: userVoteOption,
liked: liked,
votingOptionsDictionary: votingOptionsDictionary,
voteStat: voteCount,
likeCount: parseInt(countQuery.like_count),
shareCount: parseInt(countQuery.share_count),
commentCount: parseInt(countQuery.comment_count),
createdAt: post.created_at
};
});
});
});
});
});
const postData = await Promise.all(promises);
return res.json(postData);
}
catch(e){
return res.json(e)
}
}
我正在尝试 return 每个 post 的 post 数据数组。出于某种原因，它继续为这些对象打印 null，因为 return res.json 在承诺完成之前不知何故 运行。感谢任何帮助。
我以前遇到过这个问题并使用了相同的代码，但由于某种原因它对这个不起作用。
您仍然没有使用承诺，但将回调传递给 query。你不能从那些 return，Promise.all 也不会等待它们。您正在寻找
async function returnPostData(req, res, initialPostsQueryArray) {
try{
const promises = initialPostsQueryArray.map( async (post) => {
const voteCount = sumValues(post.voting_options);
const results = await pool.query(
'SELECT userhandle, image_url FROM users WHERE id = ',
[post.user_id],
]);
const userPostquery = results.rows[0];
const userHandle = userPostQuery.userhandle;
const userImageUrl = userPostQuery.image_url;
const {rows: likes } = await pool.query(
'SELECT EXISTS( SELECT 1 FROM likes WHERE user_id = AND post_id = )',
[req.user.userId, post.post_id],
);
// if the user like exists, set liked = true
const liked = likes[0].exists;
const {rows: votes} = await pool.query(
'SELECT EXISTS( SELECT 1 FROM votes WHERE user_id = AND post_id = )',
[req.user.userId, post.post_id]
);
// if the user vote exists, set voted = true and query for what they voted for
const voted = votes[0].exists;
if (voted) {
votingOptionsDictionary = post.voting_options;
const { rows } = await pool.query(
'SELECT voting_option FROM votes WHERE user_id = AND post_id = ',
[req.user.userId, post.post_id]
);
userVoteOption = rows[0].voting_option;
}
// i dont need voteCount here because that is calculated after the first query, this gets all the counts of the posts
const {rows: posts } = await pool.query(
`SELECT
posts.post_id,
COALESCE( likes.cnt, 0 ) AS like_count,
COALESCE( comments.cnt, 0 ) AS comment_count,
COALESCE( shares.cnt, 0 ) AS share_count
FROM posts
LEFT JOIN (
SELECT post_id, COUNT(*) AS cnt
FROM likes
GROUP BY post_id
) likes ON posts.post_id = likes.post_id
LEFT JOIN (
SELECT post_id, COUNT(*) AS cnt
FROM comments
GROUP BY post_id
) comments ON posts.post_id = comments.post_id
LEFT JOIN (
SELECT post_id, COUNT(*) AS cnt
FROM shares
GROUP BY post_id
) shares ON posts.post_id = shares.post_id
WHERE posts.post_id = `,
[post.post_id],
);
const countQuery = posts[0];
// final response once all above queries are done, i dont account for thread comments in comment count rn, later problem
return {
postId: post.post_id,
userHandle: userHandle,
userImageUrl: userImageUrl,
postQuestion: post.post_question,
imageUrl: post.post_image_url,
postDescription: post.post_description,
votingOptions: Object.keys(post.voting_options),
voted: voted,
userVoteOption: userVoteOption,
liked: liked,
votingOptionsDictionary: votingOptionsDictionary,
voteStat: voteCount,
likeCount: parseInt(countQuery.like_count),
shareCount: parseInt(countQuery.share_count),
commentCount: parseInt(countQuery.comment_count),
createdAt: post.created_at
};
});
const postData = await Promise.all(promises);
return res.json(postData);
}
catch(e){
return res.json(e)
}
}