The map function comes to an end once it has successfully executed once

Question

The map function comes to an end once it has successfully executed once

I am currently working on a project where I need to fetch data from MySQL, map through the array returned, and send out tweets based on certain criteria. However, my current code only sends a tweet for one element in the array when it should actually be sending multiple tweets as it iterates through all elements. Below is the snippet of my code:

array.items.map(item => {
  con.query(`SELECT username FROM users where country="${item.country}"`, async function (err, result, fields) {
    if (err) throw err;
    console.log(result);

    result.length > 0 && result.map(async user => {
      try {
        await sendTweet(`Hello ${user.username}, your selected country is ${item.country}`);
      } catch (error) {
        console.error(error.body)
        return false
      }
    })
  });
});

I seem to be having trouble with this logic. Any guidance or help would be greatly appreciated. Thank you.

javascript arrays async-await map-function

Answer 1

Answer №1

There is no necessity for async and await in this scenario.

let numbers = [4, 5, 6];
numbers.forEach(num => {

  // databaseRequest
  setTimeout(function(error, data) {
    if (error) throw error;

    data = [44, 55, 66];

    data.length > 0 && data.forEach(customer => {
      try {

        // sendEmail
        setTimeout(() => {
          console.log(`Greetings ${customer.name}, your item cost is ${num.price}`);
        }, 600);

      } catch (exception) {
        console.error(exception);
        return false;
      }
    })
  }, 600);
});

Answer 2

There is no necessity for async and await in this scenario.

let numbers = [4, 5, 6];
numbers.forEach(num => {

  // databaseRequest
  setTimeout(function(error, data) {
    if (error) throw error;

    data = [44, 55, 66];

    data.length > 0 && data.forEach(customer => {
      try {

        // sendEmail
        setTimeout(() => {
          console.log(`Greetings ${customer.name}, your item cost is ${num.price}`);
        }, 600);

      } catch (exception) {
        console.error(exception);
        return false;
      }
    })
  }, 600);
});

Answer 3

Answer №2

One possible solution is to leverage the Promise.all method.

if (result.length) {
  try {
      await Promise.all(result.map(user => {
          return sendTweet(`Greetings ${user.username}! Your chosen country is ${item.country}`);
      }));
  } catch(e) {
      //Error handling logic goes here
  }
}

Answer 4

One possible solution is to leverage the Promise.all method.

if (result.length) {
  try {
      await Promise.all(result.map(user => {
          return sendTweet(`Greetings ${user.username}! Your chosen country is ${item.country}`);
      }));
  } catch(e) {
      //Error handling logic goes here
  }
}

Answer 5

Answer №3

Here's one way I might phrase it:

In my opinion, waiting for the sendTweet function is unnecessary.

If you anticipate that a field may be undefined, you can set a default value using optional chaining methods. Please refer to optional chaining documentation for more information, specifically regarding the 'username' example provided below.

async function tweetAll(item, error, users) {
  if(error) {
    console.log('error', error.message)
  }
  else {
    for(const user of users) {
      sendTweet(`Hello ${user?.username ?? 'User'}, your selected country is ${item.country}`)
    }
  }
}

for(const item of array.items){
  con.query(`SELECT username FROM users where country="${item.country}"`, (error, users) => tweetAll(item, error, users))
}

Answer 6

Here's one way I might phrase it:

In my opinion, waiting for the sendTweet function is unnecessary.

If you anticipate that a field may be undefined, you can set a default value using optional chaining methods. Please refer to optional chaining documentation for more information, specifically regarding the 'username' example provided below.

async function tweetAll(item, error, users) {
  if(error) {
    console.log('error', error.message)
  }
  else {
    for(const user of users) {
      sendTweet(`Hello ${user?.username ?? 'User'}, your selected country is ${item.country}`)
    }
  }
}

for(const item of array.items){
  con.query(`SELECT username FROM users where country="${item.country}"`, (error, users) => tweetAll(item, error, users))
}

Answer 7

Answer №4

I don't have much experience with using MySQL in node.js, but based on your code, here's what I understand.

array.items.map(user => {
  do something async; 
});

The issue here is that the async process will only run once because the loop doesn't wait for it to complete.

Instead, you can try this approach:

array.items.forEach(async user => {
await 'do something async'
});

This way, you ensure that the async process completes before moving on. I'm not sure if MySQL supports await, but you can use Promises for handling asynchronous operations.

EDIT: If you simply want to fetch data for multiple WHERE conditions, consider optimizing your query like this:

Instead of looping through where queries, consolidate them into a single WHERE IN query.

str = '(';
arr.map(item => {
  str += item.toString();
}

str += ')';

conn.query(`SELECT * from table WHERE country IN ${str}`)

Let me know how it goes. Here's more information on SQL IN queries

Answer 8

I don't have much experience with using MySQL in node.js, but based on your code, here's what I understand.

array.items.map(user => {
  do something async; 
});

The issue here is that the async process will only run once because the loop doesn't wait for it to complete.

Instead, you can try this approach:

array.items.forEach(async user => {
await 'do something async'
});

This way, you ensure that the async process completes before moving on. I'm not sure if MySQL supports await, but you can use Promises for handling asynchronous operations.

EDIT: If you simply want to fetch data for multiple WHERE conditions, consider optimizing your query like this:

Instead of looping through where queries, consolidate them into a single WHERE IN query.

str = '(';
arr.map(item => {
  str += item.toString();
}

str += ')';

conn.query(`SELECT * from table WHERE country IN ${str}`)

Let me know how it goes. Here's more information on SQL IN queries

The map function comes to an end once it has successfully executed once

Answer №1

Answer №2

Answer №3

Answer №4

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