Enhance MongoDB to treat embedded documents as first-class entities by:

1. Automatically generating unique _id fields for embedded documents (e.g., in arrays or nested objects).
2. Supporting an optional type field to define embedded document purpose, with configurable inference.
3. Extending CRUD operations (insert, update, delete, find) to target embedded documents directly.

This simplifies managing nested data, reduces client-side logic, and improves data consistency.

Problem

Currently, MongoDB auto-generates _id fields only for top-level documents. Embedded documents (e.g., in arrays like orders) require manual ID assignment, and CRUD operations rely on array operators ($push, $pull, $set) or positional matching. This is cumbersome for complex nested structures.

Proposed Solution

1. Auto-Generated _id for Embedded Docs
   • Generate an ObjectId for embedded documents during insertion or updates, unless provided.
   • Configurable via autoGenerateSubIds: true.
2. Optional type Field
   • Allow type to categorize embedded docs (e.g., "type": "orderItem").
   • Support inference from path (e.g., orders → "orderItem") with inferType: true.
3. Extended CRUD Operations
   • New syntax:
     • insertOne({ "parent": <parent-_id>, "path": <field-path>, "doc": <embedded-doc> })
     • updateOne({ "parent": <parent-_id>, "path": <field-path>, "query": { "_id": <sub-id> }

       , "update": <update-spec> })

     • deleteOne({ "parent": <parent-_id>, "path": <field-path>, "query": { "_id": <sub-id> }

       })

     • find({ "parent": <parent-_id>, "path": <field-path>, "query": <sub-query> })
   • Example:
     javascript
     CollapseWrapCopy
     {{db.collection.insertOne({
     "parent": "parent1",
     "path": "orders",
     "doc": { "item": "Pencil", "price": 1 }

     ,
     "options": { "autoGenerateSubIds": true, "inferType": true }
     });}}Result:
     json
     CollapseWrapCopy
     {{

     { "_id": "parent1", "orders": [ \{ "_id": "auto-gen-1", "type": "orderItem", "item": "Pencil", "price": 1 }

     ]
     }}}

Use Cases

• E-commerce: Track order items with unique IDs/types.
• Content Systems: Differentiate comments or tags.
• IoT: Manage nested events/readings.

Goals

• Reduce client-side ID generation.
• Enable precise embedded doc operations.
• Improve consistency with typing.

Non-Goals

• Replace $push/$pull (opt-in feature).
• Enforce strict schemas.

Implementation Notes

• Modify src/mongo/db/ops/insert.cpp, update.cpp, query/ for _id/type and path-based ops.
• Use OID::gen() for IDs.
• Add tests in src/mongo/dbtests/.

Acceptance Criteria

1. autoGenerateSubIds: true adds unique _id to embedded docs.
2. inferType: true sets type from path.
3. CRUD ops target embedded docs by _id.
4. Existing ops unchanged without new options.
5. No performance regression.