fixes #750

lib/model/modelSet.js

@@ -23,13 +23,12 @@ function setJson(model, json, options) {
   }
 
   json = model.$parseJson(json, options);
-  const originalJson = json;
   json = model.$validate(json, options);
 
   model.$set(json);
 
   if (!options.skipParseRelations) {
-    parseRelationsIntoModelInstances(model, originalJson, options);
+    parseRelationsIntoModelInstances(model, json, options);
   }
 
   return model;
@@ -101,8 +100,9 @@ function setDatabaseJson(model, json) {
 
 function setFast(model, obj) {
   if (obj) {
-    // Don't try to set read-only virtual properties. They can easily get here through `fromJson`
-    // when parsing an object that was previously serialized from a model instance.
+    // Don't try to set read-only virtual properties. They can easily get here
+    // through `fromJson` when parsing an object that was previously serialized
+    // from a model instance.
     const readOnlyVirtuals = model.constructor.getReadOnlyVirtualAttributes();
     const keys = Object.keys(obj);
 

lib/model/modelValidate.js

@@ -1,19 +1,20 @@
 const clone = require('./modelClone').clone;
 const { defineNonEnumerableProperty } = require('./modelUtils');
 
-function validate(model, json, options) {
+function validate(model, json, options = {}) {
   json = json || model;
-  options = options || {};
+  const inputJson = json;
+  const validatingModelInstance = inputJson && inputJson.$isObjectionModel;
 
-  if (json && json.$isObjectionModel) {
+  if (options.skipValidation) {
+    return json;
+  }
+
+  if (validatingModelInstance) {
     // Strip away relations and other internal stuff.
     json = clone(json, true, true);
     // We can mutate `json` now that we took a copy of it.
-    options.mutable = true;
-  }
-
-  if (options.skipValidation) {
-    return json;
+    options = Object.assign({}, options, { mutable: true });
   }
 
   const ModelClass = model.constructor;
@@ -29,7 +30,12 @@ function validate(model, json, options) {
   json = validator.validate(args);
   validator.afterValidate(args);
 
-  return json;
+  if (validatingModelInstance) {
+    // If we cloned `json`, we need to copy the possible default values.
+    return inputJson.$set(json);
+  } else {
+    return json;
+  }
 }
 
 module.exports = {

tests/unit/model/Model.js

@@ -407,6 +407,31 @@ describe('Model', () => {
       expect(model.c).not.to.equal(obj);
     });
 
+    it('should merge default values from jsonSchema when validating a model instance', () => {
+      let obj = { a: 100, b: 200 };
+
+      Model1.jsonSchema = {
+        required: ['a'],
+        properties: {
+          a: { type: 'string', default: 'default string' },
+          b: { type: 'number', default: 666 },
+          c: { type: 'object', default: obj }
+        }
+      };
+
+      let model = Model1.fromJson({ a: 'str' }, { skipValidation: true });
+
+      expect(model.b).to.equal(undefined);
+      expect(model.c).to.equal(undefined);
+
+      model.$validate();
+
+      expect(model.a).to.equal('str');
+      expect(model.b).to.equal(666);
+      expect(model.c).to.eql(obj);
+      expect(model.c).not.to.equal(obj);
+    });
+
     // regression introduced in 0.6
     // https://github.com/Vincit/objection.js/issues/205
     it('should not throw TypeError when jsonSchema.properties == undefined', () => {