Added new Metadata Service and models

models/asset.js

@@ -46,6 +46,12 @@ const AssetSchema = new Schema({
     type: Schema.Types.Mixed,
     default: null
   },
+
+  // Additional metadata stored on the field.
+  metadata: {
+    default: {},
+    type: Object
+  }
 }, {
   versionKey: false,
   timestamps: {

models/comment.js

@@ -75,7 +75,13 @@ const CommentSchema = new Schema({
     default: 'NONE'
   },
   tags: [TagSchema],
-  parent_id: String
+  parent_id: String,
+
+  // Additional metadata stored on the field.
+  metadata: {
+    default: {},
+    type: Object
+  }
 }, {
   timestamps: {
     createdAt: 'created_at',

services/metadata.js

@@ -0,0 +1,80 @@
+/**
+ * The key must be composed of alpha characters with periods seperating them.
+ */
+const KEY_REGEX = /^(?:[A-Za-z][A-Za-z\.]*[A-Za-z])?(?:[A-Za-z]*)$/;
+
+/**
+ * Allows metadata properties to be set/unset from specific models. It is the
+ * expecatation of this API that the metadata field is either accessed later
+ * directly, or accessed as a result of another database load rather than
+ * this service providing an interface to do so.
+ *
+ * @class MetadataService
+ */
+class MetadataService {
+
+  /**
+   * Parses a key by ensuring that if it is either a string, or an array with
+   * only characters defined in the `KEY_REGEX`
+   *
+   * @static
+   * @param {String|Array} key
+   * @returns {String} string form of the key
+   *
+   * @memberOf Metadata
+   */
+  static parseKey(key) {
+    if (Array.isArray(key)) {
+      key = key.join('.');
+    }
+
+    if ((typeof key !== 'string') || !KEY_REGEX.test(key) || key.length === 0) {
+      throw new Error(`${key} is not valid, only a-zA-Z. allowed`);
+    }
+
+    return ['metadata', key].join('.');
+  }
+
+  /**
+   * Sets an object on the metadata field of an object.
+   *
+   * @static
+   * @param {mongoose.Model} model the mongoose model for the object
+   * @param {String} id the value for the field `id` of the model
+   * @param {String|Array} key key for the metadata field
+   * @param {any} value javascript object to set the value of the metadata to
+   * @returns {Promise} resolves when the update is complete
+   *
+   * @memberOf Metadata
+   */
+  static async set(model, id, key, value) {
+    key = MetadataService.parseKey(key);
+
+    return model.update({id}, {
+      $set: {
+        [key]: value
+      }
+    });
+  }
+
+  /**
+   * Removes the value for the metadata field as the specific key.
+   *
+   * @static
+   * @param {mongoose.Model} model the mongoose model for the object
+   * @param {String} id the value for the field `id` of the model
+   * @param {String|Array} key key for the metadata field
+   * @returns
+   *
+   * @memberOf Metadata
+   */
+  static async unset(model, id, key) {
+    key = MetadataService.parseKey(key);
+
+    return model.update({id}, {
+      $unset: key
+    });
+  }
+}
+
+module.exports = MetadataService;