diff --git a/models/asset.js b/models/asset.js
index 5628594bb..b8e4a7967 100644
--- a/models/asset.js
+++ b/models/asset.js
@@ -1,14 +1,23 @@
 'use strict';
 
 const mongoose = require('../mongoose');
+const uuid = require('uuid');
 const Schema = mongoose.Schema;
 
-const assetSchema = new Schema({
+const AssetSchema = new Schema({
+  id: {
+    type: String,
+    default: uuid.v4,
+    unique: true
+  },
   title: String,
   created_at: { type: Date, default: Date.now },
   updated_at: { type: Date, default: Date.now }
+},{
+  _id: false
 });
 
-const Asset = mongoose.model('Asset', assetSchema);
+const Asset = mongoose.model('Asset', AssetSchema);
 
 module.exports = Asset;
+module.exports.Schema = AssetSchema;
diff --git a/models/comments.js b/models/comments.js
index c3997cc96..c900d88cb 100644
--- a/models/comments.js
+++ b/models/comments.js
@@ -1,21 +1,27 @@
 'use strict';
 
 const mongoose = require('../mongoose');
+const uuid = require('uuid');
 const Schema = mongoose.Schema;
-const User = require('user');
-const Asset = require('asset');
+const UserSchema = require('./user').Schema;
+const AssetSchema = require('./asset').Schema;
 
-const commentSchema = new Schema({
+const CommentSchema = new Schema({
+  id: {
+    type: String,
+    default: uuid.v4,
+    unique: true
+  },
   content: {
     type: String,
     required: [true, 'The content is required.'],
     minlenght: 50
   },
-  asset: Asset,
-  author: User,
+  asset: AssetSchema,
+  author: UserSchema,
   actions: {
-    flags: [User],
-    likes: [User]
+    flags: [UserSchema],
+    likes: [UserSchema]
   },
   status: {
     type: String,
@@ -25,8 +31,29 @@ const commentSchema = new Schema({
   parent: Comment,
   created_at: { type: Date, default: Date.now },
   updated_at: { type: Date, default: Date.now }
+},{
+  _id: false
 });
 
-const Comment = mongoose.model('Comment', commentSchema);
+/**
+ * Finds a user by the id.
+ * @param {String} id  identifier of the user (uuid)
+*/
+CommentSchema.methods.findById = function(id, done) {
+  Comment.findOne({
+    id : id
+  }, (err, comment) => {
+    if (err) {
+      return done(err);
+    }
+
+    if (!comment) {
+      return done(null, false);
+    }
+    return done(null, comment);
+  });
+};
+
+const Comment = mongoose.model('Comment', CommentSchema);
 
 module.exports = Comment;
diff --git a/models/user.js b/models/user.js
index 1276f3ac2..8e626fc39 100644
--- a/models/user.js
+++ b/models/user.js
@@ -1,14 +1,23 @@
 'use strict';
 
 const mongoose = require('../mongoose');
+const uuid = require('uuid');
 const Schema = mongoose.Schema;
 
-const userSchema = new Schema({
+const UserSchema = new Schema({
+  id: {
+    type: String,
+    default: uuid.v4,
+    unique: true
+  },
   name: String,
   created_at: { type: Date, default: Date.now },
   updated_at: { type: Date, default: Date.now }
+},{
+  _id: false
 });
 
-const User = mongoose.model('User', userSchema);
+const User = mongoose.model('User', UserSchema);
 
 module.exports = User;
+module.exports.Schema = UserSchema;