title: MongoDB: remove unique constraint
body: <p>I'm trying the "Develop a RESTful API Using Node.js With Express and Mongoose" example and I ran into a problem with the MongoDB Schema:</p>
  
  <pre><code>POST: 
  { title: 'My Awesome T-shirt 2',
    description: 'All about the details. Of course it\'s black.',
    style: '12345' }
  { [MongoError: E11000 duplicate key error index: ecomm_database.products.$style_1  dup key: { : "12345" }]
    name: 'MongoError',
    err: 'E11000 duplicate key error index: ecomm_database.products.$style_1  dup key: { : "12345" }',
  </code></pre>
  
  <p>there is a unique contraint in the schema definition:</p>
  
  <pre><code>var Product = new Schema({  
      title: { type: String, required: true },  
      description: { type: String, required: true },  
      style: { type: String, unique: true },  
      modified: { type: Date, default: Date.now } });
  </code></pre>
  
  <p>how do I get rid off that? When I remove unique: true and restart the app, the schema doesn't get updated.</p>
  
  <p>How does mongodb handle "alters" to the schema?</p>