Node + Sequelize: How to check if item exists before adding? (async confusion)

问题

I am unfortunately new to node and running into some confusion regarding the asynchronous/synchronous execution of node.

I am using node, sequelize with sqlite and async.js.

I have a series of Articles, each of which has a number of Authors.

For each Authors in each Article, I'd like to check if the Author exists. If not, create it.

The problem is, on the initial run, duplicate authors are being created, I assume due to asynchronous functionality causing an issue with checking for existence.

For example, with the array: authors = ['A. Test', 'B. Test', 'C. Test', 'A. Test']

and the code:

async.each(authors, function(item, callback){
    Author.sync().then(function(){
      Author.count({ where: {name: item.trim()} }).then(function(count){
        if (count != 0) {
          console.log('Author already exists')
        } else {
          console.log('Creating author...')
          Author.create({
            name: item.trim()
          })
        }
      })
    })
  })

On the first run, will create a table:

ID | name
------------
0  | A. Test
1  | B. Test
2  | C. Test
3  | A. Test

What am I doing wrong? I seem to be missing a fundamental concept of asynchronous vs synchronous execution in Node.

(I've also tried async.eachSeries which is supposed to execute in series rather than in parallel?)

Edit: Slightly refactored, but still creating duplicates

async.eachSeries(authors, function(authorName, callback){
    Author.findOne({ where: {name: authorName.trim()} }).
    then(function(author){
      if (author) {
        // Author exists...
        callback()
      } else {
        // Author does not exist...
        Author.create({
          name: authorName.trim()
        }).then(function(author){
          callback()
        })
      }
    })
  })

回答1:

Author.count isn't really needed, unless you need the count. See findOrCreate().

With findOrCreate() you could have the following. (Edited trex005's snippet for this)

async.eachSeries(authors, function(item, callback) {
  Author.sync().then(function() {
    Author.findOrCreate({
      where: {
        name: item.trim()
      },
      defaults: { // set the default properties if it doesn't exist
        name: item.trim()
      }
    }).then(function(result) {
      var author = result[0], // the instance of the author
        created = result[1]; // boolean stating if it was created or not

      if (!created) { // false if author already exists and was not created.
        console.log('Author already exists');
      }

      console.log('Created author...');
      callback();
    });
  })
})

回答2:

Change your each to eachSeries and actually call the callback and you should be golden.

async.eachSeries(authors, function(item, callback){
    Author.sync().then(function(){
      Author.count({ where: {name: item.trim()} }).then(function(count){
        if (count != 0) {
          console.log('Author already exists')
          callback(); //assuming you want it to keep looping, if not use callback(new Error("Author already exists"))
        } else {
          console.log('Creating author...')
          Author.create({
            name: item.trim()
          }).then(function(author){
            callback();
          })
        }
      })
    })
  })

来源：https://stackoverflow.com/questions/31815076/node-sequelize-how-to-check-if-item-exists-before-adding-async-confusion

标签

javascript

node.js

asynchronous

sequelize.js

async.js