title: Mongo db aggregation multiple conditions
body: <p>I want to project a collection applying exporting a value only if a field is inside a range.</p>
  
  <p>Sort of:</p>
  
  <pre><code>db.workouts.aggregate({
   $match: { user_id: ObjectId(".....") }
  },
  {
   $project: { 
          '20': { $cond: [ {$gt: [ "$avg_intensity", 20]} , '$total_volume', 0] }
      }    
   })
  </code></pre>
  
  <p>I need to get the value only if the avg_intensity is inside a certain range. I will then group and sum on the projection result.</p>
  
  <p>What I am trying to do is applying a $gt and $lt filter but with no much success.</p>
  
  <pre><code>db.workouts.aggregate(
  {
     $match: { user_id: ObjectId("....") }
  },
  {
  $project: { 
          '20': { $cond: [ [{$gt: [ "$avg_intensity", 20]}, {$lt: [ "$avg_intensity", 25]}] ,    '$total_volume', 0] }
      }    
   })
  </code></pre>
  
  <p>How may I apply both $gt and $lt conditions?</p>