fix(document): retain user-defined key order on initial set with nest…

…ed docs

Fix #6944

lib/document.js

@@ -708,6 +708,17 @@ Document.prototype.$set = function $set(path, val, type, options) {
     const pathName = prefix + key;
     pathtype = this.schema.pathType(pathName);
 
+    // On initial set, delete any nested keys if we're going to overwrite
+    // them to ensure we keep the user's key order.
+    if (type === true &&
+        !prefix &&
+        path[key] != null &&
+        pathtype === 'nested' &&
+        this._doc[key] != null &&
+        Object.keys(this._doc[key]).length === 0) {
+      delete this._doc[key];
+    }
+
     if (path[key] !== null &&
         path[key] !== void 0 &&
         // need to know if plain object - no Buffer, ObjectId, ref, etc

test/schema.select.test.js

@@ -396,7 +396,7 @@ describe('schema select option', function() {
       }), 'gh7017');
 
       return co(function*() {
-        yield db;
+        yield db.$initialConnection;
         yield db.collection('gh7017').insertOne({
           a: 'foo',
           b: 'bar',