Add increment and decrement to instance

src/instance.js

@@ -289,6 +289,66 @@ fakeModelInstance.prototype.update = function (obj) {
 	return this.save();
 };
 
+/**
+ * Increment
+ * @instance
+ * @param {String|Array|Object} fields
+ * @param {Object} [options]
+ * @param {Object} [options.by = 1] The number to increment by
+ * @return {Promise<instance>}
+ */
+fakeModelInstance.prototype.increment = function (fields, options) {
+    if (!Array.isArray(fields) && typeof fields === 'object') {
+        for (let k in fields) {
+            this.increment(k, { by: fields[k] });
+        }
+
+        return bluebird.resolve(this);
+    }
+
+    if (typeof fields === 'string') {
+        fields = [fields];
+    } 
+
+    let by = typeof options !== 'undefined' ? options.by || 1 : 1;
+
+    for(let i = 0; i <= fields.length; i++) {
+        this._values[fields[i]] += by;
+    }
+
+    return bluebird.resolve(this);
+};
+
+/**
+ * Decrement
+ * @instance
+ * @param {String|Array|Object} fields
+ * @param {Object} [options]
+ * @param {Object} [options.by = 1] The number to decrement by
+ * @return {Promise<instance>}
+ */
+fakeModelInstance.prototype.decrement = function (fields, options) {
+    if (!Array.isArray(fields) && typeof fields === 'object') {
+        for (let k in fields) {
+            this.decrement(k, { by: fields[k] });
+        }
+
+        return bluebird.resolve(this);
+    }
+
+    if (typeof fields === 'string') {
+        fields = [fields];
+    } 
+
+    let by = typeof options !== 'undefined' ? options.by || 1 : 1;
+
+    for(let i = 0; i <= fields.length; i++) {
+        this._values[fields[i]] -= by;
+    }
+
+    return bluebird.resolve(this);
+};
+
 /**
  * Returns all the values in a JSON representation.
  * 

test/instance.spec.js

@@ -280,7 +280,149 @@ describe('Instance', function () {
 			}).catch(done);
 		});
 	});
-
+
+    describe('#increment', () => {
+        it('should increment field passed by 1', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 3,
+            };
+
+            inst.increment('foo');
+
+            inst._values.foo.should.equal(4);
+        });
+
+        it('should increment field passed by 2', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 3,
+            };
+
+            inst.increment('foo', { by: 2 });
+
+            inst._values.foo.should.equal(5);
+        });
+
+        it('should increment fields passed by 1', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 3,
+                bar: 2,
+            };
+
+            inst.increment(['foo', 'bar']);
+
+            inst._values.foo.should.equal(4);
+            inst._values.bar.should.equal(3);
+        });
+
+        it('should increment fields passed by 2', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 3,
+                bar: 2,
+            };
+
+            inst.increment(['foo', 'bar'], { by: 2 });
+
+            inst._values.foo.should.equal(5);
+            inst._values.bar.should.equal(4);
+        });
+
+        it('should increment fields as dicto', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 2,
+                bar: 2,
+            };
+
+            inst.increment({
+                foo: 2,
+                bar: 3,
+            });
+
+            inst._values.foo.should.equal(4);
+            inst._values.bar.should.equal(5);
+        });
+    });
+
+    describe('#decrement', () => {
+        it('should decrement field passed by 1', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 3,
+            };
+
+            inst.decrement('foo');
+
+            inst._values.foo.should.equal(2);
+        });
+
+        it('should decrement field passed by 2', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 3,
+            };
+
+            inst.decrement('foo', { by: 2 });
+
+            inst._values.foo.should.equal(1);
+        });
+
+        it('should decrement fields passed by 1', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 3,
+                bar: 2,
+            };
+
+            inst.decrement(['foo', 'bar']);
+
+            inst._values.foo.should.equal(2);
+            inst._values.bar.should.equal(1);
+        });
+
+        it('should decrement fields passed by 2', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 3,
+                bar: 2,
+            };
+
+            inst.decrement(['foo', 'bar'], { by: 2 });
+
+            inst._values.foo.should.equal(1);
+            inst._values.bar.should.equal(0);
+        });
+
+        it('should decrement fields as dicto', () => {
+            let inst = new Instance();
+
+            inst._values = {
+                foo: 2,
+                bar: 2,
+            };
+
+            inst.decrement({
+                foo: 2,
+                bar: 3,
+            });
+
+            inst._values.foo.should.equal(0);
+            inst._values.bar.should.equal(-1);
+        });
+    });
+
 	describe('#toJSON', function () {
 		it('should have the function aliased to toJson', function () {
 			var inst = new Instance();