Fix: cast id parameter based on schema _id type in DocumentArray.id()

[Lex-Ashu]

Closes #15724

Summary

The DocumentArray.id() method was always attempting to cast the id parameter to ObjectId, which caused issues when using custom _id types like String, Number, or Object. This fix implements schema-based casting by:

1. Getting the _id schema type from the document array schema
2. Casting the input id parameter to match that type before comparison
3. Maintaining backward compatibility with ObjectId fallback

This resolves the TODO comment at line 124 and ensures the method works correctly with all _id types that Mongoose supports.

Example demonstrating the fix:

// Schema with custom String _id
const CustomSchema = new Schema({
  _id: { type: String, required: true },
  name: String,
});

const ParentSchema = new Schema({ children: [CustomSchema] });
const Parent = mongoose.model("Parent", ParentSchema);

// Create a parent document with a child
const parent = new Parent({ children: [{ _id: "abc123", name: "test" }] });
await parent.save();

// Before this fix, parent.children.id('abc123') would fail to find the document
// because 'abc123' would be incorrectly cast to an ObjectId.
// After this fix, it correctly casts 'abc123' to a String and finds the document.
const found = parent.children.id("abc123");
console.log(found); // Will now correctly output the embedded document: { _id: 'abc123', name: 'test' }

[vkarpov15]

Good overall direction, just have a few suggestions

[Copilot]

Pull Request Overview

This PR implements schema-based casting for the id() method in the DocumentArray type, addressing a TODO comment that was previously in the code. The implementation now attempts to cast the input id parameter using the schema's _id field type before performing comparisons.

Key changes:

• Adds schema-aware casting of the input id parameter using the _id field's schema type
• Refactors the comparison logic to use the casted id value for more accurate matching
• Removes the TODO comment indicating this feature has been implemented

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[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 4 comments.

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[Copilot]

[nitpick] The fallback condition else if (castedId == null && (id == _id || utils.deepEqual(id, _id))) could potentially match when casting failed but the original id happens to match. This might give false positives if the intent is that casting failure should prevent matches.

Consider whether this fallback is necessary, or if a failed cast should always result in no match. If the fallback is intentional, a comment explaining why would be helpful.

Suggested change

	} else if (castedId == null && (id == _id || utils.deepEqual(id, _id))) {
	return val;

[Copilot]

[nitpick] The comparison logic starting at line 170 handles multiple scenarios but lacks explanatory comments. Consider adding brief comments for each condition to improve maintainability:

// Both castedId and _id are non-ObjectId types (e.g., string, number, object)
} else if (castedId != null && !isBsonType(castedId, 'ObjectId') && !isBsonType(_id, 'ObjectId')) {
  if (castedId == _id || utils.deepEqual(castedId, _id)) {
    return val;
  }
// Both castedId and _id are ObjectIds - compare as strings
} else if (castedId != null && isBsonType(castedId, 'ObjectId') && isBsonType(_id, 'ObjectId')) {
  if (castedId.toString() === _id.toString()) {
    return val;
  }
// Mixed types or other valid castedId scenarios
} else if (castedId != null && castedId == _id) {
  return val;
// Fallback to original id when casting failed
} else if (castedId == null && (id == _id || utils.deepEqual(id, _id))) {
  return val;
}

[vkarpov15]

LGTM, I'll merge this into a separate branch so I can do some cleanup but otherwise I will merge this into 8.20.