From c9cf1fae258a97eb65fd74890a964f8670c8f18b Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Tue, 29 Nov 2022 15:57:21 -0500
Subject: [PATCH 1/4] fix(query): handle deselecting _id when another field has
 schema-level `select: false`

Fix #12670
---
 lib/queryhelpers.js                |  3 +++
 test/model.field.selection.test.js | 23 +++++++++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/lib/queryhelpers.js b/lib/queryhelpers.js
index 62a8cb5b1f4..1cd4832156b 100644
--- a/lib/queryhelpers.js
+++ b/lib/queryhelpers.js
@@ -163,6 +163,9 @@ exports.applyPaths = function applyPaths(fields, schema) {
       if (!isDefiningProjection(field)) {
         continue;
       }
+      if (keys[keyIndex] === '_id') {
+        continue;
+      }
       exclude = !field;
       break;
     }
diff --git a/test/model.field.selection.test.js b/test/model.field.selection.test.js
index 2a2352b7db2..2ae5c97312f 100644
--- a/test/model.field.selection.test.js
+++ b/test/model.field.selection.test.js
@@ -475,7 +475,6 @@ describe('model field selection', function() {
     db.deleteModel(/BlogPost/);
     const BlogPost = db.model('BlogPost', BlogPostSchema);
 
-
     await BlogPost.create({
       author: 'me',
       settings: {
@@ -497,8 +496,6 @@ describe('model field selection', function() {
   });
 
   it('when `select: true` in schema, works with $elemMatch in projection', async function() {
-
-
     const productSchema = new Schema({
       attributes: {
         select: true,
@@ -524,12 +521,10 @@ describe('model field selection', function() {
   });
 
   it('selection specified in query overwrites option in schema', async function() {
-
     const productSchema = new Schema({ name: { type: String, select: false } });
 
     const Product = db.model('Product', productSchema);
 
-
     await Product.create({ name: 'Computer' });
 
     const product = await Product.findOne().select('name');
@@ -538,7 +533,6 @@ describe('model field selection', function() {
   });
 
   it('selecting with `false` instead of `0` doesn\'t overwrite schema `select: false` (gh-8923)', async function() {
-
     const userSchema = new Schema({
       name: { type: String, select: false },
       age: { type: Number }
@@ -552,4 +546,21 @@ describe('model field selection', function() {
 
     assert.ok(!user.name);
   });
+
+  it('handles deselecting _id when other field has schema-level `select: false` (gh-12670)', async function() {
+    const schema = new mongoose.Schema({
+      field1: {
+        type: String,
+        select: false
+      },
+      field2: String
+    });
+    const User = db.model('User', schema);
+
+    await User.create({ field1: 'test1', field2: 'test2' });
+    const doc = await User.findOne().select('field2 -_id');
+    assert.ok(doc.field2);
+    assert.strictEqual(doc.field1, undefined);
+    assert.strictEqual(doc._id, undefined);
+  });
 });

From 582b09155dace2b55d0509e1aebbd2a675acbd05 Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Tue, 29 Nov 2022 16:55:31 -0500
Subject: [PATCH 2/4] test: fix tests

---
 test/model.field.selection.test.js | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/test/model.field.selection.test.js b/test/model.field.selection.test.js
index 2ae5c97312f..6a4bb45adc0 100644
--- a/test/model.field.selection.test.js
+++ b/test/model.field.selection.test.js
@@ -548,6 +548,13 @@ describe('model field selection', function() {
   });
 
   it('handles deselecting _id when other field has schema-level `select: false` (gh-12670)', async function() {
+    const version = await start.mongodVersion();
+    // Test fails with "Projection cannot have a mix of inclusion and exclusion."
+    // in MongoDB < 5
+    if (version[0] < 5) {
+      return this.skip();
+    }
+
     const schema = new mongoose.Schema({
       field1: {
         type: String,

From 89141a011565c7b12c284853b0b8d7941300f2e8 Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Tue, 29 Nov 2022 18:03:51 -0500
Subject: [PATCH 3/4] fix tests

---
 lib/queryhelpers.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/queryhelpers.js b/lib/queryhelpers.js
index 1cd4832156b..6948715a03c 100644
--- a/lib/queryhelpers.js
+++ b/lib/queryhelpers.js
@@ -163,7 +163,9 @@ exports.applyPaths = function applyPaths(fields, schema) {
       if (!isDefiningProjection(field)) {
         continue;
       }
-      if (keys[keyIndex] === '_id') {
+      // `_id: 1, name: 0` is a mixed inclusive/exclusive projection in
+      // MongoDB 4.0 and earlier, but not in later versions.
+      if (keys[keyIndex] === '_id' && keys.length > 1) {
         continue;
       }
       exclude = !field;

From 686096d60df51542e3b0f80680b03a205dc2a1cd Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Wed, 30 Nov 2022 11:21:43 -0500
Subject: [PATCH 4/4] test: remove probably unnecessary check for MongoDB 4

---
 test/model.field.selection.test.js | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/test/model.field.selection.test.js b/test/model.field.selection.test.js
index 6a4bb45adc0..2ae5c97312f 100644
--- a/test/model.field.selection.test.js
+++ b/test/model.field.selection.test.js
@@ -548,13 +548,6 @@ describe('model field selection', function() {
   });
 
   it('handles deselecting _id when other field has schema-level `select: false` (gh-12670)', async function() {
-    const version = await start.mongodVersion();
-    // Test fails with "Projection cannot have a mix of inclusion and exclusion."
-    // in MongoDB < 5
-    if (version[0] < 5) {
-      return this.skip();
-    }
-
     const schema = new mongoose.Schema({
       field1: {
         type: String,