Summary

The JSON editor removes _id then $sets the remaining map. Fields the user deleted in JSON remain in the document. Nested replacements also cannot drop keys.

Scope

• Persist via replaceOne (whole document except _id) or compute $unset for keys present in the original and absent in the edited JSON.
• Keep _id immutable.
• Test: start {a:1,b:2}, save {a:1} → b is gone.

Out of scope

• Inspector single-field $set (correct for that path).