Can't find documents searching by ObjectId using Mongoose

  Campaign.find {client_id:req.param('client_id')}, (error, campaigns) ->
    if error
      response =
        error: error.message
    else
      for campaign in campaigns
        query =
          campaign_id: campaign._id
        console.log query
        CampaignResponse.find query, (err, campaignResponsesCount) ->
          console.log campaignResponsesCount
          
      response = campaigns
      
    res.json response

For some reason, this returns no results. However, there are items in CampaignResponse with that specific campaign._id. I'm pretty sure this is an issue with types and casting, but I can't figure out what to do.

Any help?

A couple tips:

• Try running the same query from mongodb at the command line, see if you get any results.
• Is the "campaign_id" defined as an ObjectId in your schema? If so, try searching using the ObjectId type.

For example:

var ObjectId = require('mongoose').Types.ObjectId; 
var query = { campaign_id: new ObjectId(campaign._id) };

Just to improve the previous (correct) answer, i use on my projects :

String.prototype.toObjectId = function() {
  var ObjectId = (require('mongoose').Types.ObjectId);
  return new ObjectId(this.toString());
};

// Every String can be casted in ObjectId now
console.log('545f489dea12346454ae793b'.toObjectId());

Instead of using ObjectId to find by comparing your parameters simply use

Campaign.findById {req.param('client_id'),function(err,docs)}....

when finding docs using objectId findById is the most efficient way of all...