Hack to fake single subdoc field in a mongoose schema

mongoose-single-subdoc.js

// mongoose doesn't like single embedded schemas
// it likes them as arrays of an embedded schema
// so this is a cheater hack to fake a single subdoc
// it creates a field named `_yourField` and a virtual named `yourField`
// and it makes sure the array keeps just one element in it
// USAGE EXAMPLE:
/* 
  var models = require('models')
    , ChildSchema = models.ChildSchema
    , singleSubdoc = require('mongoose-single-subdoc');
  ;
  var ParentSchema = new Schema({ _child: [ChildSchema] });
  ParentSchema.plugin(singleSubdoc, {
    child1: ChildSchema,
    child2: ChildSchema
  });
*/
module.exports = function(schema, fields) {
  for(var virtualName in fields) {
    var realName = '_' + virtualName;
    var schemaType = fields[virtualName];

    schema.add({ realName: schemaType });

    schema.virtual(virtualName)
      .get(function() {
        if(this[realName].length) return this[realName][0];
        else return null;
      })
      .set(function(value) {
        this[realName] = [value];
      })
    ;
  }
};