Merge pull request #5740 from AyushG3112/addFields-aggregate-feature

Add $addFields pipeline operator via a Mongoose Function

Author: vkarpov15

lib/aggregate.js

@@ -106,6 +106,41 @@ Aggregate.prototype.append = function() {
   return this;
 };
 
+/**
+ * Appends a new $addFields operator to this aggregate pipeline.
+ * Requires MongoDB v3.4+ to work
+ *
+ * ####Examples:
+  *
+ *     // adding new fields based on existing fields
+ *     aggregate.addFields({
+ *         newField: '$b.nested'
+ *       , plusTen: { $add: ['$val', 10]}
+ *       , sub: {
+ *            name: '$a'
+ *         }
+ *     })
+ *
+ *     // etc
+ *     aggregate.addFields({ salary_k: { $divide: [ "$salary", 1000 ] } });
+ *
+ * @param {Object} arg field specification
+ * @see $addFields https://docs.mongodb.com/manual/reference/operator/aggregation/addFields/
+ * @return {Aggregate}
+ * @api public
+ */
+Aggregate.prototype.addFields = function(arg) {
+  var fields = {};
+  if (typeof arg === 'object' && !util.isArray(arg)) {
+    Object.keys(arg).forEach(function(field) {
+      fields[field] = arg[field];
+    });
+  } else {
+    throw new Error('Invalid addFields() argument. Must be an object');
+  }
+  return this.append({$addFields: fields});
+};
+
 /**
  * Appends a new $project operator to this aggregate pipeline.
  *

package-lock.json

@@ -444,6 +444,19 @@ describe('aggregate: ', function() {
       });
     });
 
+    describe('addFields', function() {
+      it('(object)', function(done) {
+        var aggregate = new Aggregate();
+
+        assert.equal(aggregate.addFields({ a: 1, b: 1, c: 0 }), aggregate);
+        assert.deepEqual(aggregate._pipeline, [{ $addFields: { a: 1, b: 1, c: 0 } }]);
+
+        aggregate.addFields({ d: {$add: ['$a','$b']} });
+        assert.deepEqual(aggregate._pipeline, [{ $addFields: { a: 1, b: 1, c: 0 } }, { $addFields: { d: {$add: ['$a','$b']} } }]);
+        done();
+      });
+    });
+
     describe('facet', function() {
       it('works', function(done) {
         var aggregate = new Aggregate();