title: How to push field into embedded document
body: <p>Model</p>
  
  <pre><code>var ModuleSchema = new Schema({
      name: String,
      types: [{
          name: String,
          functions: [{
              name: String
          }]
      }]    
  });
  
  var CoverageSchema = new Schema({
      name: String,
      modules: [{
          name: String,
          types: [{
              name: String,
              functions: [{
                  name: String,
                  coverages: [{
                      blocksCovered: Number
                  }]
              }]
          }]    
  });
  
  mongoose.model('Module', ModuleSchema);
  mongoose.model('Coverage', CoverageSchema);
  </code></pre>
  
  <p>coverage.server.controller.js</p>
  
  <pre><code>coverage.modules = []; // Mongoose CoverageSchema existing object.
  
  Module.findOne(...).exec(function(err, module) {
       // If not error
       coverage.modules.push({
           name: module.name, 
           types: module.types
       });
  
       // How do I add 'coverage.modules.types.functions.coverages: [] ?
       coverage.modules.forEach(function(mod){
           mod.types.forEach(function(type){
              type.functions.forEach(function(func){
                  func.coverages.push({blocksCovered: 0}); // Error: coverages undefined.
              });
           });
       });
  
       coverage.save(function (err) ...);
  });
  </code></pre>
  
  <p>I am able to save coverage object with inserted modules from ModuleSchema.
  However cannot add after it modules.types.functions.coverages embedded document before save.</p>