Add replication example

example/replication/app.js

@@ -0,0 +1,138 @@
+var loopback = require('../../');
+var app = loopback();
+var db = app.dataSource('db', {connector: loopback.Memory});
+var Color = app.model('color', {dataSource: 'db', options: {trackChanges: true}});
+var Color2 = app.model('color2', {dataSource: 'db', options: {trackChanges: true}});
+var target = Color2;
+var source = Color;
+var SPEED = process.env.SPEED || 100;
+var conflicts;
+
+var steps = [
+
+  createSomeInitialSourceData,
+
+    replicateSourceToTarget,
+    list.bind(this, source, 'current SOURCE data'),
+    list.bind(this, target, 'current TARGET data'),
+
+  updateSomeTargetData,
+
+    replicateSourceToTarget,
+    list.bind(this, source, 'current SOURCE data '),
+    list.bind(this, target, 'current TARGET data (includes conflicting update)'),
+
+  updateSomeSourceDataCausingAConflict,
+
+    replicateSourceToTarget,
+    list.bind(this, source, 'current SOURCE data (now has a conflict)'),
+    list.bind(this, target, 'current TARGET data (includes conflicting update)'),
+
+  resolveAllConflicts,
+
+    replicateSourceToTarget,
+    list.bind(this, source, 'current SOURCE data (conflict resolved)'),
+    list.bind(this, target, 'current TARGET data (conflict resolved)'),
+
+  createMoreSourceData,
+
+    replicateSourceToTarget,
+    list.bind(this, source, 'current SOURCE data'),
+    list.bind(this, target, 'current TARGET data'),
+
+  createEvenMoreSourceData,
+
+    replicateSourceToTarget,
+    list.bind(this, source, 'current SOURCE data'),
+    list.bind(this, target, 'current TARGET data'),
+
+  deleteAllSourceData,
+
+    replicateSourceToTarget,
+    list.bind(this, source, 'current SOURCE data (empty)'),
+    list.bind(this, target, 'current TARGET data (empty)'),
+
+  createSomeNewSourceData,
+
+    replicateSourceToTarget,
+    list.bind(this, source, 'current SOURCE data'),
+    list.bind(this, target, 'current TARGET data')
+];
+
+run(steps);
+
+function createSomeInitialSourceData() {
+  Color.create([
+    {name: 'red'},
+    {name: 'blue'},
+    {name: 'green'}
+  ]);
+}
+
+function replicateSourceToTarget() {
+  Color.replicate(0, Color2, {}, function(err, replicationConflicts) {
+    conflicts = replicationConflicts;
+  });
+}
+
+function resolveAllConflicts() {
+  if(conflicts.length) {
+    conflicts.forEach(function(conflict) {
+      conflict.resolve();
+    });
+  }
+}
+
+function updateSomeTargetData() {
+  Color2.findById(1, function(err, color) {
+    color.name = 'conflict';
+    color.save();
+  });
+}
+
+function createMoreSourceData() {
+  Color.create({name: 'orange'});
+}
+
+function createEvenMoreSourceData() {
+  Color.create({name: 'black'});
+}
+
+function updateSomeSourceDataCausingAConflict() {
+  Color.findById(1, function(err, color) {
+    color.name = 'red!!!!';
+    color.save();
+  });
+}
+
+function deleteAllSourceData() {
+  Color.destroyAll();
+}
+
+function createSomeNewSourceData() {
+  Color.create([
+    {name: 'violet'},
+    {name: 'amber'},
+    {name: 'olive'}
+  ]);
+}
+
+function list(model, msg) {
+  console.log(msg);
+  model.find(function(err, items) {
+    items.forEach(function(item) {
+      console.log(' -', item.name);
+    });
+    console.log();
+  });
+}
+
+function run(steps) {
+  setInterval(function() {
+    var step = steps.shift();
+    if(step) {
+      console.log(step.name);
+      step();
+    }
+  }, SPEED);
+}

lib/models/change.js

@@ -27,7 +27,7 @@ var properties = {
  */
 
 var options = {
-
+  trackChanges: false
 };
 
 /**
@@ -55,6 +55,12 @@ Change.CREATE = 'create';
 Change.DELETE = 'delete';
 Change.UNKNOWN = 'unknown';
 
+/*!
+ * Conflict Class
+ */
+
+Change.Conflict = Conflict;
+
 /*!
  * Setup the extended model.
  */
@@ -149,13 +155,34 @@ Change.findOrCreate = function(modelName, modelId, callback) {
 
 Change.prototype.rectify = function(cb) {
   var change = this;
-  this.prev = this.rev;
-  // get the current revision
-  this.currentRevision(function(err, rev) {
-    if(err) return Change.handleError(err, cb);
-    change.rev = rev;
+  var tasks = [
+    updateRevision,
+    updateCheckpoint
+  ];
+
+  if(this.rev) this.prev = this.rev;
+
+  async.parallel(tasks, function(err) {
+    if(err) return cb(err);
     change.save(cb);
   });
+
+  function updateRevision(cb) {
+    // get the current revision
+    change.currentRevision(function(err, rev) {
+      if(err) return Change.handleError(err, cb);
+      change.rev = rev;
+      cb();
+    });
+  }
+
+  function updateCheckpoint(cb) {
+    change.constructor.getCheckpointModel().current(function(err, checkpoint) {
+      if(err) return Change.handleError(err);
+      change.checkpoint = ++checkpoint;
+      cb();
+    });
+  }
 }
 
 /**
@@ -233,7 +260,7 @@ Change.prototype.type = function() {
 
 Change.prototype.getModelCtor = function() {
   // todo - not sure if this works with multiple data sources
-  return this.constructor.modelBuilder.models[this.modelName];
+  return loopback.getModel(this.modelName);
 }
 
 /**
@@ -306,7 +333,10 @@ Change.diff = function(modelName, since, remoteChanges, callback) {
     if(err) return callback(err);
     var deltas = [];
     var conflicts = [];
+    var localModelIds = [];
+
     localChanges.forEach(function(localChange) {
+      localModelIds.push(localChange.modelId);
       var remoteChange = remoteChangeIndex[localChange.modelId];
       if(!localChange.equals(remoteChange)) {
         if(remoteChange.isBasedOn(localChange)) {
@@ -317,9 +347,91 @@ Change.diff = function(modelName, since, remoteChanges, callback) {
       }
     });
 
+    modelIds.forEach(function(id) {
+      if(localModelIds.indexOf(id) === -1) {
+        deltas.push(remoteChangeIndex[id]);
+      }
+    });
+
     callback(null, {
       deltas: deltas,
       conflicts: conflicts
     });
   });
 }
+
+/**
+ * Correct all change list entries.
+ * @param  {Function} callback
+ */
+
+Change.rectifyAll = function(cb) {
+  // this should be optimized
+  this.find(function(err, changes) {
+    if(err) return cb(err);
+    changes.forEach(function(change) {
+      change.rectify();
+    });
+  });
+}
+
+/**
+ * Get the checkpoint model.
+ * @return {Checkpoint}
+ */
+
+Change.getCheckpointModel = function() {
+  var checkpointModel = this.Checkpoint;
+  if(checkpointModel) return checkpointModel;
+  this.checkpoint = checkpointModel = require('./checkpoint').extend('checkpoint');
+  checkpointModel.attachTo(this.dataSource);
+  return checkpointModel;
+}
+
+
+/**
+ * When two changes conflict a conflict is created.
+ *
+ * **Note: call `conflict.fetch()` to get the `target` and `source` models.
+ * 
+ * @param {Change} sourceChange The change object for the source model
+ * @param {Change} targetChange The conflicting model's change object
+ * @property {Model} source The source model instance
+ * @property {Model} target The target model instance
+ */
+
+function Conflict(sourceChange, targetChange) {
+  this.sourceChange = sourceChange;
+  this.targetChange = targetChange;
+}
+
+Conflict.prototype.fetch = function(cb) {
+  var conflict = this;
+  var tasks = [
+    getSourceModel,
+    getTargetModel
+  ];
+
+  async.parallel(tasks, cb);
+
+  function getSourceModel(change, cb) {
+    conflict.sourceModel.getModel(function(err, model) {
+      if(err) return cb(err);
+      conflict.source = model;
+      cb();
+    });
+  }
+
+  function getTargetModel(cb) {
+    conflict.targetModel.getModel(function(err, model) {
+      if(err) return cb(err);
+      conflict.target = model;
+      cb();
+    });
+  }
+}
+
+Conflict.prototype.resolve = function(cb) {
+  this.sourceChange.prev = this.targetChange.rev;
+  this.sourceChange.save(cb);
+}

lib/models/checkpoint.js

@@ -48,8 +48,9 @@ Checkpoint.current = function(cb) {
   this.find({
     limit: 1,
     sort: 'id DESC'
-  }, function(err, checkpoint) {
+  }, function(err, checkpoints) {
     if(err) return cb(err);
+    var checkpoint = checkpoints[0] || {id: 0};
     cb(null, checkpoint.id);
   });
 }