Refactoring pattern in javascript

Question

I am writing a small application and which communicates with the DB, instead of using callback pattern I am using Promises to simplify my code. Having done a fair amount of coding I can now see some pattern very frequently in my code, I need to know how can I refactor it so that the similar logic is at a single place.

  var queryString = "select * from users u inner join "+
      "(select user_id, count(id) cnt from applications "+
      "where id in (select id from applications where "+
      "created_at > current_date - interval '1 week') "+
      "group by user_id) a on u.id = a.user_id order by a.cnt desc";
  var self = this;
  return new Promise(function _promise(resolve, reject) {
    req.client.query(queryString, [], function result(error, result) {
      req.done(error);

      if (error) {
        console.log('error ' + error.message);
        return reject(error);
      }
      var users = result.rows.map(function(row) {
        return new User(row);
      });
      resolve(users);
    });
  });

The above pattern is my every method the only thing that varies is the content after if, is there any functional approach I can use to refactor it out?

Adding one more example:

  var queryString = 'select c.id, c.name, t.contact_user '+
    'from companies c, teams t '+
    'where t.user_id = $1::int and t.company_id = c.id '+
    'limit $2::int';
  var self = this;
  return new Promise(function _promise(resolve, reject) {
    req.client.query( queryString, [self.id, User._RESOURCE_LIMIT],
        function result(error, result) {
      req.done(error);
      if (error) {
        console.log('Error ' + error.message);
        return reject(error);
      }

      self._companies = result.rows.map(function (data) {
        return new Company(data);
      });
      resolve(self);
    });
  });

@JaromandaX I think that will be variable too, let me correct the description. — CodeYogi
– CodeYogi, Commented Feb 28, 2017 at 3:55

Jaromanda X · Accepted Answer · 2017-02-28 04:00:37Z

1

Promisified "query" function

let query = (req, queryString, arg = []) => new Promise((resolve, reject) => {
    req.client.query(queryString, arg, (error, result) => {
        req.done(error);
        if (error) {
            return reject(error);
        }
        resolve(result);
    });
});

Usage (as per example in the question)

query(req, "select * .... etc")
.then(result => {
    return result.rows.map(function(row) {
        return new User(row);
    });
})
.catch(reason => {
    // error handling goes here
});

edited Feb 28, 2017 at 4:00

answered Feb 28, 2017 at 3:57

Jaromanda X

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5 Comments

CodeYogi Over a year ago

The array after queryString will not be always empty, but yes I got your point.

Jaromanda X Over a year ago

another argument then - let me rewrite it

Jaromanda X Over a year ago

If the ES2015+ code isn't to your liking, I can transpile it for you :p

CodeYogi Over a year ago

Its fine, I can infer it.

CodeYogi Over a year ago

I think you can help me out in this codereview.stackexchange.com/q/156417/58341

Rahul Arora · Accepted Answer · 2017-02-28 04:19:56Z

0

You can do something like this:

function queryDb(queryString, arr) {
    var arr = arr || [];
    return new Promise(function _promise(resolve, reject) {
        req.client.query(queryString, arr, function result(error, result) {
            req.done(error);
            if (error) {
                console.log('Error ' + error.message);
                return reject(error);
            }
            resolve(result);
        });
    });
}

queryDb("queryString", arr).then(function(response){ //calling the function everytime like this
    //do stuff here
}, function(error){
    //handle error
})

edited Feb 28, 2017 at 4:19

answered Feb 28, 2017 at 4:13

Rahul Arora

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1 Comment

Mulan Over a year ago

Don't log the error here. Just reject it and allow it to be logged by the error handler, if desired.

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