如何让代码等待循环的执行

Question

下面是我的getUser函数

const getUsers = async (req, res) => {
try {
ddb.get({
TableName: "Tablename",
Key: { Username: req.query.username }
},(err,user) => {
if(err || Object.keys(user).length === 0) {
return res.status(404).json("Something went wrong")
} else {
const userSociety = Object.keys(user.Item.Societies)[0]
ddb.get({
TableName: "Tablename",
Key: { SocietyCode: userSociety }
},(err, society) => {
if(err || Object.keys(society).length === 0) {
return res.status(400).json({ message: "Could not fetch society members" })
} else {
const users = Object.keys(society.Item.SocietyMembers)
const usersData = []
users.forEach(async u => {
ddb.get({
TableName: "TestMyMohallaUsers",
Key: { Username: u }
},async (err,user) => {
if(err || Object.keys(user).length === 0) {
} else usersData.push({
Username: user.Item.Username,
Firstname: user.Item.Name
})
})
})
return res.status(200).json({ message: "Data detched successfully", Users: usersData })
}
})
}
})
} catch (error) {
return res.status(500).json({ error: "Internal Server Error" })
}
}

我想等待forEach的执行，然后通过return语句发回数据，但到目前为止，return语句给出了空的用户数组。

很明显，我的代码不是在等待forEach的执行然后返回数据。有人帮我怎么办？

编辑：ddb是DynamoDB 的一个实例

Answer 1

如果

• 使用DynamoDB Promise API而不是回调的金字塔
• 将代码重构为几个函数
• 最后，等待所有用户获取完成需要Promise.all来完成所有这些承诺

async function getUser(ddb, username) {
const user = await ddb
.get({
TableName: "TestMyMohallaUsers",
Key: { Username: username },
})
.promise();
if (!user.Item) {
throw new Error(`User ${username} not found`);
}
return user.Item;
}
async function getSociety(ddb, societyCode) {
const society = await ddb
.get({
TableName: "Tablename",
Key: { SocietyCode: societyCode },
})
.promise();
if (!society.Item) {
throw new Error(`Society ${societyCode} not found`);
}
return society.Item;
}
const getUsers = async (req, res) => {
try {
const user = await getUser(ddb, req.params.username);
const userSocietyCode = Object.keys(user.Societies)[0];
const society = await getSociety(ddb, userSocietyCode);
const societyUsers = Object.keys(society.SocietyMembers);
const usersData = await Promise.all(
societyUsers.map(async (member) => {
const user = await getUser(ddb, member);
return {
Username: user.Username,
Firstname: user.Name,
};
}),
);
return res
.status(200)
.json({
message: "Data detched successfully",
Users: usersData,
});
} catch (e) {
return res
.status(400)
.json({ message: `Could not fetch information: ${e}` });
}
};