title: Create another Model for storing nested data
body: <p>I have a user schema like this:</p>
  <pre><code>const schema = new Schema({
  
      name: String,
      email: { type: String, trim: true, index: true, unique: true, sparse: true },
      
      cards: {
          starter : [unitSchema], 
          intermediate : [unitSchema], 
          advanced : [unitSchema] 
      },
  
  });
  </code></pre>
  <p>The user schema contains specific cards for that user as arrays of starter and intermediate level etc.. right?</p>
  <p>Then we have the <code>unitSchema</code> which is actually an object containing cards of the specific unit for instance we can store cards for unit 1 or cards of the unit 2 or 3 here right?</p>
  <pre><code>const unitSchema = new Schema(
      {
          unit: Number,
          cards: [cardSchema]
      }
  );
  </code></pre>
  <p>And finally we have our <code>cardSchema</code> containing cards:</p>
  <p>Please note that each card is completely unique. I mean a card can be considered as a single document in the database. it's a card containing information about <code>performance</code> etc of that user for the card.</p>
  <pre><code>const cardSchema = new Schema(
      {
          id: String, // like main-12-45
          unit: Number, // same as unit of unitSchema
          performance: [Number],
          type: {
              module: String,
              model: String, 
              method: String,
          },
          ease: { type: Number, default: 2.5 },
          currentInterval: { type: Number, default: 1 },
          interact: {
              pauseTimes: [Number],
              recordTimes: [{ start: Number, end: Number }],
              recordingStorage: { x: [Number], y: [Number] },
              initialPositions: { left: String, top: String }
          },
     
      }
  );
  </code></pre>
  <p>As you see so far I just nested the data and it works great. But I want to <strong>store each card in the different Model</strong>.</p>
  <p>To be honest I don't want to, I need to! because MongoDB has <strong>limitation of 16 MB</strong> for each document and I cannot store such a big data nested inside <code>users model</code>.</p>
  <p>How can I create a new model named <code>Cards</code> and have the same structure as above. (All the code I wrote is based on the nested structure as above any major change in the structure costs me weeks)</p>