fix(document): make validateUpdatedOnly option handle pre-existing …

…errors

Fix #8091

lib/document.js

@@ -2075,8 +2075,22 @@ Document.prototype.$__validate = function(options, callback) {
 
   const _this = this;
   const _complete = () => {
-    const err = this.$__.validationError;
+    let err = this.$__.validationError;
     this.$__.validationError = undefined;
+
+    if (shouldValidateModifiedOnly && err != null) {
+      // Remove any validation errors that aren't from modified paths
+      const errors = Object.keys(err.errors);
+      for (const errPath of errors) {
+        if (!this.isModified(errPath)) {
+          delete err.errors[errPath];
+        }
+      }
+      if (Object.keys(err.errors).length === 0) {
+        err = void 0;
+      }
+    }
+
     this.$__.cachedRequired = {};
     this.emit('validate', _this);
     this.constructor.emit('validate', _this);

test/document.test.js

@@ -2351,6 +2351,24 @@ describe('document', function() {
       });
     });
 
+    it('validateModifiedOnly with pre existing validation error (gh-8091)', function() {
+      const schema = mongoose.Schema({
+        title: String,
+        coverId: Number
+      }, { validateModifiedOnly: true });
+
+      const Model = db.model('gh8091', schema);
+
+      return co(function*() {
+        yield Model.collection.insertOne({ title: 'foo', coverId: parseFloat('not a number') });
+
+        const doc = yield Model.findOne();
+        doc.title = 'bar';
+        // Should not throw
+        yield doc.save();
+      });
+    });
+
     it('handles non-errors', function(done) {
       const schema = new Schema({
         name: { type: String, required: true }