models: move Change LDL def into a json file

common/models/change.js

@@ -10,26 +10,6 @@ var PersistedModel = require('../../lib/loopback').PersistedModel
   , assert = require('assert')
   , debug = require('debug')('loopback:change');
 
-/*!
- * Properties
- */
-
-var properties = {
-  id: {type: String, id: true},
-  rev: {type: String},
-  prev: {type: String},
-  checkpoint: {type: Number},
-  modelName: {type: String},
-  modelId: {type: String}
-};
-
-/*!
- * Options
- */
-
-var options = {
-  trackChanges: false
-};
 
 /**
  * Change list entry.
@@ -41,11 +21,11 @@ var options = {
  * @property {String} modelName Model name
  * @property {String} modelId Model ID
  *
- * @class
- * @inherits {Model}
+ * @class Change
+ * @inherits {PersistedModel}
  */
 
-var Change = module.exports = PersistedModel.extend('Change', properties, options);
+module.exports = function(Change) {
 
   /*!
    * Constants
@@ -501,6 +481,7 @@ Change.prototype.getModel = function(callback) {
    * @param {PersistedModel} TargetModel
    * @property {ModelClass} source The source model instance
    * @property {ModelClass} target The target model instance
+   * @class Change.Conflict
    */
 
   function Conflict(modelId, SourceModel, TargetModel) {
@@ -644,3 +625,4 @@ Conflict.prototype.type = function(cb) {
       return cb(null, Change.UNKNOWN);
     });
   }
+};

common/models/change.json

@@ -0,0 +1,25 @@
+{
+  "name": "Change",
+  "trackChanges": false,
+  "properties": {
+    "id": {
+      "type": "string",
+      "id": true
+    },
+    "rev": {
+      "type": "string"
+    },
+    "prev": {
+      "type": "string"
+    },
+    "checkpoint": {
+      "type": "number"
+    },
+    "modelName": {
+      "type": "string"
+    },
+    "modelId": {
+      "type": "string"
+    }
+  }
+}

lib/builtin-models.js

@@ -33,7 +33,9 @@ module.exports = function(loopback) {
     require('../common/models/user.json'),
     require('../common/models/user.js'));
 
-  loopback.Change = require('../common/models/change');
+  loopback.Change = createModel(
+    require('../common/models/change.json'),
+    require('../common/models/change.js'));
 
   loopback.Checkpoint = createModel(
     require('../common/models/checkpoint.json'),

lib/persisted-model.js

@@ -960,7 +960,10 @@ PersistedModel.enableChangeTracking = function() {
 }
 
 PersistedModel._defineChangeModel = function() {
-  var BaseChangeModel = require('./../common/models/change');
+  var BaseChangeModel = loopback.Change;
+  assert(BaseChangeModel,
+    'Change model must be defined before enabling change replication');
+
   return this.Change = BaseChangeModel.extend(this.modelName + '-change',
     {},
     {