fix(query): allow deselecting discriminator key using - syntax

Fix #13760

Author: vkarpov15

lib/queryhelpers.js

@@ -199,6 +199,7 @@ exports.applyPaths = function applyPaths(fields, schema) {
       // projection if `name` has schema-level `select: true`.
       if ((!type || !type.selected) || exclude !== false) {
         fields[path] = 0;
+        exclude = true;
       } else if (type && type.selected && exclude === false) {
         // Make a note of minus paths that are overwriting paths that are
         // included by default.

test/query.test.js

@@ -4171,14 +4171,22 @@ describe('Query', function() {
     assert.equal(q.op, 'findOneAndReplace');
   });
 
-  it('allows deselecting discriminator key (gh-13679)', async function() {
-    const testSchema = new Schema({ name: String });
+  it('allows deselecting discriminator key (gh-13760) (gh-13679)', async function() {
+    const testSchema = new Schema({ name: String, age: Number });
     const Test = db.model('Test', testSchema);
     const Test2 = Test.discriminator('Test2', new Schema({ test: String }));
 
     const { _id } = await Test2.create({ name: 'test1', test: 'test2' });
     const { name, __t } = await Test.findById(_id).select({ __t: 0 });
     assert.strictEqual(name, 'test1');
     assert.strictEqual(__t, undefined);
+
+    let doc = await Test.findById(_id).select({ __t: 0, age: 0 });
+    assert.strictEqual(doc.name, 'test1');
+    assert.strictEqual(doc.__t, undefined);
+
+    doc = await Test.findById(_id).select(['-__t', '-age']);
+    assert.strictEqual(doc.name, 'test1');
+    assert.strictEqual(doc.__t, undefined);
   });
 });