title: Mongodb,express find data by _id with multiple condition
body: <p>My code is shown below:</p>
  
  <pre><code>PostCategory.find({categoryid:category._id.str},function(err,postcategories){
              if(err) return next(err);
  
              Post.find({_id:postcategories.postid},function(err,posts){
              if(err) return next(err);
                  return res.render(__dirname + "/views/categorydetail",  {
                      title: 'İletişim',
                      stylesheet: 'contact'
                  });
              }); 
          });
  </code></pre>
  
  <p>I want to find all post which _id is in postcategories.postid. My postcategories returns me list. Here is my postcategories model:</p>
  
  <pre><code>module.exports = function(){
      var PostCategorySchema = new mongoose.Schema({
          postid:String,
          categoryid:String,
          createddate:{ type: Date, default: Date.now }
      });
  
      mongoose.model("PostCategory",PostCategorySchema);
  };
  </code></pre>
  
  <p>Any idea?</p>