feat: added persistDefaultValues (#1815)

Ignores value if it matches default value.

lib/model.js

@@ -299,6 +299,10 @@ ModelBaseClass.prototype._initProperties = function(data, options) {
       }
     }
 
+    if (ignoresMatchedDefault(properties[p]) && properties[p].default === propVal) {
+      delete self.__data[p];
+    }
+
     // Set default value using a named function
     if (applyDefaultValues && propVal === undefined) {
       const defn = properties[p].defaultFn;
@@ -362,6 +366,13 @@ ModelBaseClass.prototype._initProperties = function(data, options) {
   this.trigger('initialize');
 };
 
+// Implementation of persistDefaultValues property
+function ignoresMatchedDefault(property) {
+  if (property && property.persistDefaultValues === false) {
+    return true;
+  }
+}
+
 // Helper function for determing the applyDefaultOnWrites value of a property
 function appliesDefaultsOnWrites(property) {
   if (property && ('applyDefaultOnWrites' in property)) {

test/defaults.test.js

@@ -131,4 +131,48 @@ describe('defaults', function() {
       found.qualities.length.should.equal(1);
     });
   });
+
+  context('persistDefaultValues', function() {
+    it('removes property if value matches default', async () => {
+      const Apple = db.define('Apple', {
+        color: {type: String, default: 'red', persistDefaultValues: false},
+        taste: {type: String, default: 'sweet'},
+      }, {applyDefaultsOnReads: false});
+
+      const apple = await Apple.create({color: 'red', taste: 'sweet'});
+      const found = await Apple.findById(apple.id);
+      should(found.color).be.undefined();
+      found.taste.should.equal('sweet');
+    });
+
+    it('removes property if value matches default in an object', async () => {
+      const Apple = db.define('Apple', {
+        name: {type: String},
+        qualities: {
+          color: {type: String, default: 'red', persistDefaultValues: false},
+          taste: {type: String, default: 'sweet'},
+        },
+      }, {applyDefaultsOnReads: false});
+
+      const apple = await Apple.create({name: 'Honeycrisp', qualities: {taste: 'sweet'}});
+      const found = await Apple.findById(apple.id);
+      should(found.qualities.color).be.undefined();
+      found.qualities.taste.should.equal('sweet');
+    });
+
+    it('removes property if value matches default in an array', async () => {
+      const Apple = db.define('Apple', {
+        name: {type: String},
+        qualities: [
+          {color: {type: String, default: 'red', persistDefaultValues: false}},
+          {taste: {type: String, default: 'sweet'}},
+        ],
+      }, {applyDefaultsOnReads: false});
+
+      const apple = await Apple.create({name: 'Honeycrisp', qualities: [{taste: 'sweet'}]});
+      const found = await Apple.findById(apple.id);
+      should(found.qualities[0].color).be.undefined();
+      found.qualities.length.should.equal(1);
+    });
+  });
 });