Uncovering the main document and all predecessor records in MongoDB

I am in the process of creating a publication that will provide me with a series of documents from the collection. The relationship between these documents can be seen below:

{ 
    "_id" : "peRuJcPMDzZgTvWSX", 
    "author" : "author", 
    "type" : "article", 
    "parent" : "mnfTFfZ7Fqcu6ZJ7T", 
    "ancestors" : [ "hbSycmNNvmdqvpchX", "mnfTFfZ7Fqcu6ZJ7T" ] 
}
{ 
    "_id" : "mnfTFfZ7Fqcu6ZJ7T", 
    "article" : "article", 
    "parent" : "hbSycmNNvmdqvpchX", 
    "ancestors" : [ "hbSycmNNvmdqvpchX" ] 
}
{ 
    "_id" : "hbSycmNNvmdqvpchX", 
    "title" : "title", 
    "ancestors" : [ ] 
}

My objective is to retrieve all ancestors in the publication based on the ID of the first document.

Meteor.publish('list', function(id) {
    check(id, String);
    return Collection.find({}); // this returns ALL documents (wrong)
    return Collection.find({ _id: id }) // this only fetches the first document (main) (wrong)
    // I NEED: The main document and all its ancestors
});

Answer №1

To retrieve data, start with a .findOne() query and then return an array of cursors:

Meteor.publish('list', function(id) {
  check(id, String);
  const ancestors = Collection.findOne(id).ancestors;
  if ( ancestors ){
    return [ Collection.find(id), Collection.find({_id: {$in: ancestors}})];
  } else {
    return Collection.find(id);
  }
});

Alternatively, you could achieve the same result with a single .find() query using an $or operator, but this might impact performance.

Answer №2

If you're looking to establish a join relationship in your Meteor project, you may find the publish-composite package useful:

Meteor.publishComposite('list', function(id) {
  // Implement necessary checks here ...

  return {
    find() {
      return Collection.find(id);
    },
    children: [{
      find(doc) {
        return Collection.find({
          _id: {
            $in: doc.ancestors
          }
        });
      },
    }],
  };
});

This package ensures that your publication is reactive. For example, if there are changes in the ancestors array, the data sent to the client will be updated accordingly. If you simply use findOne without utilizing publish-composite, any changes in the ancestors list won't be reflected in the data transmitted to the client.

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