Remove observers from Model on end of the stream

- Remove flags and properly finish the stream.
 - Destroy emits an end event for compability with ending of
   ReadableStream now.
 - Check for default implementation of destroy() method,
   because in Node.js 8 all types of streams have a native one.

lib/persisted-model.js

@@ -1851,79 +1851,84 @@ module.exports = function(registry) {
     var idName = this.getIdName();
     var Model = this;
     var changes = new PassThrough({objectMode: true});
-    var writeable = true;
 
-    changes.destroy = function() {
-      changes.removeAllListeners('error');
-      changes.removeAllListeners('end');
-      writeable = false;
-      changes = null;
+    changes._destroy = function() {
+      changes.end();
+      changes.emit('end');
+      changes.emit('close');
     };
 
-    changes.on('error', function() {
-      writeable = false;
-    });
-    changes.on('end', function() {
-      writeable = false;
-    });
+    changes.destroy = changes.destroy || changes._destroy; // node 8 compability
+
+    changes.on('error', removeHandlers);
+    changes.on('close', removeHandlers);
+    changes.on('finish', removeHandlers);
+    changes.on('end', removeHandlers);
 
     process.nextTick(function() {
       cb(null, changes);
     });
 
-    Model.observe('after save', createChangeHandler('save'));
-    Model.observe('after delete', createChangeHandler('delete'));
+    Model.observe('after save', changeHandler);
+    Model.observe('after delete', deleteHandler);
 
-    function createChangeHandler(type) {
-      return function(ctx, next) {
-        // since it might have set to null via destroy
-        if (!changes) {
-          return next();
-        }
+    function changeHandler(ctx, next) {
+      var change = createChangeObject(ctx, 'save');
+      changes.write(change);
 
-        var where = ctx.where;
-        var data = ctx.instance || ctx.data;
-        var whereId = where && where[idName];
+      next();
+    };
 
-        // the data includes the id
-        // or the where includes the id
-        var target;
+    function deleteHandler(ctx, next) {
+      var change = createChangeObject(ctx, 'delete');
+      changes.write(change);
 
-        if (data && (data[idName] || data[idName] === 0)) {
-          target = data[idName];
-        } else if (where && (where[idName] || where[idName] === 0)) {
-          target = where[idName];
-        }
+      next();
+    };
 
-        var hasTarget = target === 0 || !!target;
+    function createChangeObject(ctx, type) {
+      var where = ctx.where;
+      var data = ctx.instance || ctx.data;
+      var whereId = where && where[idName];
 
-        var change = {
-          target: target,
-          where: where,
-          data: data,
-        };
+      // the data includes the id
+      // or the where includes the id
+      var target;
 
-        switch (type) {
-          case 'save':
-            if (ctx.isNewInstance === undefined) {
-              change.type = hasTarget ? 'update' : 'create';
-            } else {
-              change.type = ctx.isNewInstance ? 'create' : 'update';
-            }
+      if (data && (data[idName] || data[idName] === 0)) {
+        target = data[idName];
+      } else if (where && (where[idName] || where[idName] === 0)) {
+        target = where[idName];
+      }
 
-            break;
-          case 'delete':
-            change.type = 'remove';
-            break;
-        }
+      var hasTarget = target === 0 || !!target;
 
-        // TODO(ritch) this is ugly... maybe a ReadableStream would be better
-        if (writeable) {
-          changes.write(change);
-        }
-
-        next();
+      var change = {
+        target: target,
+        where: where,
+        data: data,
       };
+
+      switch (type) {
+        case 'save':
+          if (ctx.isNewInstance === undefined) {
+            change.type = hasTarget ? 'update' : 'create';
+          } else {
+            change.type = ctx.isNewInstance ? 'create' : 'update';
+          }
+
+          break;
+        case 'delete':
+          change.type = 'remove';
+          break;
+      }
+
+      return change;
+    }
+
+    function removeHandlers() {
+      Model.removeObserver('after save', changeHandler);
+      Model.removeObserver('after delete', deleteHandler);
     }
   };
 

test/change-stream.test.js

@@ -5,6 +5,7 @@
 
 'use strict';
 var expect = require('./helpers/expect');
+var sinon = require('sinon');
 var loopback = require('../');
 
 describe('PersistedModel.createChangeStream()', function() {
@@ -20,6 +21,8 @@ describe('PersistedModel.createChangeStream()', function() {
       });
     });
 
+    afterEach(verifyObserversRemoval);
+
     it('should detect create', function(done) {
       var Score = this.Score;
 
@@ -27,7 +30,6 @@ describe('PersistedModel.createChangeStream()', function() {
         changes.on('data', function(change) {
           expect(change.type).to.equal('create');
           changes.destroy();
-
           done();
         });
 
@@ -67,6 +69,32 @@ describe('PersistedModel.createChangeStream()', function() {
         });
       });
     });
+
+    it('should not emit changes after destroy', function(done) {
+      var Score = this.Score;
+
+      var spy = sinon.spy();
+
+      Score.createChangeStream(function(err, changes) {
+        changes.on('data', function() {
+          spy();
+          changes.destroy();
+        });
+
+        Score.create({team: 'foo'})
+          .then(() => Score.deleteAll())
+          .then(() => {
+            expect(spy.calledOnce);
+            done();
+          });
+      });
+    });
+
+    function verifyObserversRemoval() {
+      var Score = this.Score;
+      expect(Score._observers['after save']).to.be.empty();
+      expect(Score._observers['after delete']).to.be.empty();
+    }
   });
 
   // TODO(ritch) implement multi-server support