Changing the behavior of virtual only queries

If only virtual fields are present in the `select` statement, no real properties will be retrieved from the database.

README.md

@@ -7,6 +7,7 @@ Allows you to specify which virtuals fields should be returned in find queries w
 ### Note
 * The plugin has no effect on non-lean queries
 * Queries can be set as lean using any style, e.g. `myQuery.lean()`, `myQuery.setOptions({ lean: true })`, `myQuery.lean({virtuals: true})`, etc.
+* If only virtual fields are present in the `select` statement, no real properties will be retrieved from the database.
 * Specifying a virtual field in the `select` statement will exclude non-specified virtual fields, even if lean is set to `{virtuals: true}` (which would normally trigger all virtuals to be included). `Model.find({}, 'virtual_key').lean()` is the same as `.lean({ virtuals: ['virtual_key']})`.
 
 ## Getting Started

index.js

@@ -19,6 +19,15 @@ module.exports = function selectVirtuals(schema) {
         this._mongooseOptions.lean = {};
       }
       this._mongooseOptions.lean.virtuals = virtualFields;
+
+      // At this point there was at least one virtual field mentioned in the selection. If
+      // there are no more fields left in the selection, it means only virtual fields
+      // were selected and we shouldn't return any real fields. We need to explcitly set
+      // only the `_id` field to come back since leaving the selection object blank would
+      // return all real fields.
+      if (Object.keys(selection).length === 0) {
+        selection['_id'] = 1;
+      }
     }
 
     next();

tests/index.test.js

@@ -34,6 +34,13 @@ test('Virtual field in select, lean set to `true`', async t => {
   t.is(result.virtual_key2, undefined);
 });
 
+test('Only a virtual field is in the select', async t=> {
+  const result = await Model.findOne({}, 'virtual_key1').lean().exec();
+  t.is(result.real_key, undefined, 'Real fields should be excluded if not specified');
+  t.is(result.virtual_key1, 'v_val1');
+  t.is(result.virtual_key2, undefined);
+});
+
 test('Query is not lean', async t => {
   const result = await Model.findOne({}, 'real_key virtual_key1').exec();
   t.is(result.real_key, 'foo', 'Real properties should be returned');