CODEWITHSUNDEEP
javascriptnode.jsasynchronouscallbackpromise
Sameer
Sameer

Reputation: 3526

Use callback or promise to make async code to work like sync in nodejs

My nodejs api function:

exports.userSignup = (req, res) => {
  const home = {
    address: req.body.name,
    phoneno: req.body.code,
  };
  Home.create(home)
    .then((data) => {
      createUser()
        // i want to complete the above createUser() function fully then only i need to move to this below then function

        .then(() => {
          const loginDetails = {
            username: 'stackoverflow',
          };
          User.create(loginDetails)
            .then((data) => {
              return res.status(200).send(data);
            }).catch((err) => {
              console.log('error while create schema:', err);
            });
        });

    })
    .catch((err) => {
      console.log('err:', err);
    });
};

My createUser function code:

const createUser = () => {
  Home.findAll({
    raw: true,
  }).then((data) => {
    data.forEach((client) => {
      postgresDB.createSchema(client.code).then(() => {
        Object.keys(postgresDB.models).forEach((currentItem) => {
          postgresDB.models[currentItem].schema(client.code).sync();
        });
        console.log('Postgres schema created');
      }).catch((err) => {
        console.log(err);
      });
    });
  }).catch((err) => {
    console.log('Warning:', err.message);
  });
};
createUser();

But this one is working as asynchronous,

How to make this using promise resolve reject or callback?

See my code, i made a comment which needs to work first,

I tried with async await but not working!

Upvotes: 1

Views: 1717

Answers (4)

Jeeva
Jeeva

Reputation: 1590

You can use async and await in createUser function. You can alter your function by Using promise, We can able to either resolve or reject. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function

Upvotes: -1

vkarpov15
vkarpov15

Reputation: 3872

If async/await doesn't quite work for you, just use promise chaining. It's super painful to see people just write callback based code with promises and forget that you can chain promises by returning a promise from the onFulfilled() parameter to then():

const createUser = () => {
  return Home.findAll({ raw: true }).
    then(data => {
      return Promise.all(data.map(client => postgresDB.createSchema(client.code)));
    }).
    then(() => {
      const keys = Object.keys(postgresDBModels);
      return Promise.all(keys.map(currentItem => {
        return postgresDB.models[currentItem].schema(client.code).sync();
      }));
    }).
    then(() => console.log('Postgres schema created')).
    catch((err) => {
      console.log(err);
    });
};
createUser();

Upvotes: 0

Swati Anand
Swati Anand

Reputation: 899

The problem lies in the synchronous data.forEach() call inside the createUser function which doesn't wait for the async createSchema calls to finish before returning. You can fix this by using an async implementation of forEach function or by using Promise.all()

Here's a piece of code that might work for you:

const createUser = () => {
  return Home.findAll({
    raw: true
  }).then((data) => Promise.all(
    data.map((client) => postgresDB.createSchema(client.code).then(() =>
      Promise.all(Object.keys(postgresDB.models).map((currentItem) =>
        postgresDB.models[currentItem].schema(client.code).sync()
      ))
    ))
  ))
    .catch((err) => {
      console.log('Warning:', err.message);
    });
};

Upvotes: 1

Jake Miller
Jake Miller

Reputation: 2642

In order for promise chaining to work, you have to return a promise for any asynchronous functions or else it won't wait. You're also making another asynchronous call for each client you iterate through. In order to deal with multiple promises at once, you need to push each promise into an array and pass it to Promise.all. Here's a snippet that should work.

const createUser = () => {
  return Home.findAll({
    raw: true,
  }).then((data) => {
    const promises = [];
    data.forEach((client) => {
      promises.push(
        postgresDB.createSchema(client.code).then(() => {
          Object.keys(postgresDB.models).forEach((currentItem) => {
             postgresDB.models[currentItem].schema(client.code).sync();
             console.log('Postgres schema created');
          })
        })
      );
    });
    return Promise.all(promises);
  }).catch((err) => {
    console.log('Warning:', err.message);
  });
};

Upvotes: 2

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