CODEWITHSUNDEEP
javascriptmongodbmeteor
funkyeah
funkyeah

Reputation: 3174

mongo find selector causes unmatching results to be returns

userLink_titles = Entries.find({ _id:"bxSbMgszYxbCqDonF"})

returns:

  docs: Object
    CBqHrJvTE8xz7u2Rz: Object
      _id: "CBqHrJvTE8xz7u2Rz"
      author: "AHSwfYgeGmur9oHzu"
    Q8m7PMbQr62E3A73f: Object
      _id: "Q8m7PMbQr62E3A73f"
      author: "AHSwfYgeGmur9oHzu"
    bxSbMgszYxbCqDonF: Object
      _id: "bxSbMgszYxbCqDonF"
      author: "AHSwfYgeGmur9oHzu"

As you can see it returns the correct document but it also returns incorrect documents.

findOne: userLink_titles = Entries.findOne({ _id:"bxSbMgszYxbCqDonF"}) works as expected and only returns the correct document.

I would use the findOne except that the end intention is to make the _id selector an array such that find would return the documents for all documents that match the _id selectors in the array.

Bonus Points:

Let's say I wanted to retrieve the titles of a set of articles, where the references to those articles (the _ids of the Articles in their Articles collection) have been saved in a user collection.

So effectively I would retrieve the Article references from the user collection, and use those references to retrieve the titles of Articles from the Articles collection.

What would the code/pseudo code look like for that? Something like the following (I am assuming the below is a complete bastardization of some best practices for querying/retrieving records)

user_profile = Users.findOne({username : "Frank"});
user_saved_articles_ids = user_profile.findOne({saved_articles_ids});
userLinks = Articles.find({ _id:user_saved_articles_ids});
userLinksTitles = Articles.find({titles});

Upvotes: 0

Views: 837

Answers (2)

alanning
alanning

Reputation: 5217

For those interested in the bonus question, you want MongoDB's $in operator.

If this will be used in a publish method on the server then you may want to check out publish-with-relations.

Something like the function below would be an efficient way to retrieve the information. It makes two calls to the database. Using the fields parameter prevents unnecessary data from being sent between the db and the webserver.

/**
 * Titles of a User's saved articles
 * 
 * @method getSavedTitles
 * @param {String} username
 * @return {Array} a list of article titles
 */
function getSavedTitles (username) {
  var user,
      ids,
      linkedArticles,
      titles;

  user = Users.findOne({username: username}, 
                       {fields:{ _id:0, profile:1 }});

  if (!user || !user.profile) {
    throw new Meteor.Error(500, 'Missing user profile');
  }

  ids = user.profile.savedArticleIds;

  if (!ids || !_.isArray(ids)) {
    throw new Meteor.Error(500, 'Missing saved article ids');
  }

  linkedArticles = Articles.find({_id: {$in: ids}},
                        {fields:{ _id:0, title:1 }});

  titles = _.pluck(linkedArticles.fetch(), "title");

  return titles;

}  // end getSavedTitles

Upvotes: 2

avital
avital

Reputation: 1542

If you want to inspect the results of a query in the console, use Entries.find(...).fetch()

Entries.find() returns a cursor, which is a construct used to render lists efficiently, so that only the entries that change need to be re-rendered. Returning cursors from helpers on which you use {{#each}} will lead to more responsive apps.

Upvotes: 1

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