fix(create): allow foreign key to be null when association reference is set (#9466)

lib/instance-validator.js

@@ -6,6 +6,7 @@ const Utils = require('./utils');
 const sequelizeError = require('./errors');
 const Promise = require('./promise');
 const DataTypes = require('./data-types');
+const BelongsTo = require('./associations/belongs-to');
 const _ = require('lodash');
 
 /**
@@ -320,6 +321,8 @@ class InstanceValidator {
    */
   _validateSchema(rawAttribute, field, value) {
     if (rawAttribute.allowNull === false && (value === null || value === undefined)) {
+      const association = _.values(this.modelInstance.constructor.associations).find(association => association instanceof BelongsTo && association.foreignKey === rawAttribute.fieldName);
+      if (!association || !this.modelInstance.get(association.associationAccessor)) {
         const validators = this.modelInstance.validators[field];
         const errMsg = _.get(validators, 'notNull.msg', `${this.modelInstance.constructor.name}.${field} cannot be null`);
 
@@ -332,6 +335,7 @@ class InstanceValidator {
           'is_null'
         ));
       }
+    }
 
     if (rawAttribute.type === DataTypes.STRING || rawAttribute.type instanceof DataTypes.STRING || rawAttribute.type === DataTypes.TEXT || rawAttribute.type instanceof DataTypes.TEXT) {
       if (Array.isArray(value) || _.isObject(value) && !(value instanceof Utils.SequelizeMethod) && !Buffer.isBuffer(value)) {

test/integration/model/create/include.test.js

@@ -60,6 +60,39 @@ describe(Support.getTestDialectTeaser('Model'), () => {
         });
       });
 
+      it('should create data for BelongsTo relations with no nullable FK', function () {
+        const Product = this.sequelize.define('Product', {
+          title: Sequelize.STRING
+        });
+        const User = this.sequelize.define('User', {
+          first_name: Sequelize.STRING
+        });
+
+        Product.belongsTo(User, {
+          foreignKey: {
+            allowNull: false
+          }
+        });
+
+        return this.sequelize.sync({ force: true }).then(() => {
+          return Product.create({
+            title: 'Chair',
+            User: {
+              first_name: 'Mick'
+            }
+          }, {
+            include: [{
+              model: User
+            }]
+          }).then(savedProduct => {
+            expect(savedProduct).to.exist;
+            expect(savedProduct.title).to.be.equal('Chair');
+            expect(savedProduct.User).to.exist;
+            expect(savedProduct.User.first_name).to.be.equal('Mick');
+          });
+        });
+      });
+
       it('should create data for BelongsTo relations with alias', function() {
         const Product = this.sequelize.define('Product', {
           title: Sequelize.STRING