Mongoose add array of objects

Question

I am creating a simple blog which have posts containing tags.

var postSchema = new Schema ({
  title: { type: String, required: true },
  content: { type: String, required: true },
  tags: [{ type: Schema.Types.ObjectId, ref: 'Tag' }]
});

When a user publishes a post I get the tags as an array of tag names. How can I loop through these tags and create them and add them to the post when it is first saved?

I have tried this:

var post = Post({
  title: data.title,
  content: data.content
});

data.tags.forEach(function(name) {
  Tag.findOrCreate({ name: name }, function(err, tag, created) {
    post.tags.push(tag);

    post.save(function(err) {
      if (err) throw err;

      console.log('Post saved!');
    });
  });
});

But that forces me to save the post again for each tag. Is there a way to only save once?

Blakes Seven · Accepted Answer · 2015-07-19 02:33:03Z

2

Well you can of course call .save() only once, just move it to after processing the loop. But of course since all call here are "asynchronous" then what you need better control of that so you know when the callback to each operation is completed:

Using the async library as a helper here:

var post = Post({
  title: data.title,
  content: data.content
});

async.eachLimit(data.tags, 5, function(name,callback) {
    Tag.findOrCreate({ "name": name },function(err,tag) {
        if (err) callback(err);
        post.tags.push(tag);
        callback();
    });        
},function(err) {
   if (err) throw err;   // or some handling as all errors come here
   post.save(function(err,post) {

   })
});

So the async.eachLimit there allows a "callback" to be fired on each completion of the processed array element. The "limit" part actually makes sure only that many operations are run at the same time so you don't go eating up your stack or available connections.

When all items in the list are processed and there callback functions returned then the final block there is executed, therefore when all items have either been created or found and the respective data pushed to the array ready for saving.

In the same way, if any "error" occurs in that loop then execution is handed to that final block in order to handle all error actions in the one place as well.

answered Jul 19, 2015 at 2:33

Blakes Seven

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1 Comment

Blakes Seven Over a year ago

@ProvocativePanda If you have other questions then please post them using the Ask Question link. You just learned that you need "flow control" that respects the asynchronous execution. If you have more specific questions to ask them form them and post them and someone will answer.

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