title: how to add dynamic field to existing collection using mongoose
body: <p>I am trying to create a mongodb collection called products in which I have fields (id, name, price and properties) and now different products have different kind of properties for example iphone has different set of properties when compared to nike shoes. So how to define a schema and add dynamically new key and value pair using mongoose.</p>
  
  <pre><code>{
    "_id":"001",
    "name":"iphone 5",
    "price":$650,
    "properties":{
      'weight':2.3, 
      'talktime': '8 hours', 
      'battery type': 'lithium'
    }
  }
  
  
  {
    "_id":"002",
    "name":"nike shoes",
    "price":$80,
    "properties":{
      'size':10, 
      'color':black
    }
  }
  </code></pre>