title: Mongoose find() RegExp for Number type field
body: <p>I'm try to create a table with filters and when i need find rows through regular expression i have error below.
  How i can use RegExp with field type of Number? Change field type on String, is a good idea?</p>
  
  <pre><code>var ContractSchema = new Schema({
    userId: {type: Schema.Types.ObjectId, ref: 'User'},
    number: Number,
    // ...
  });
  
  module.exports = mongoose.model('Contract', ContractSchema);
  
  Contract.find({number: /555/}, function(err, contracts){
    console.log(err, contracts);
  });
  </code></pre>
  
  <blockquote>
    <p>Cast to number failed for value "/555/" at path "number"</p>
  </blockquote>