C100DBA CRUD Operations Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  db.inventory.insertOne( { sku: "A100", qty: 5 } )

  Why this is correct

  insertOne inserts the document and, because sku has a unique index, a duplicate value causes a duplicate key error to be thrown. This is the simplest correct approach: no extra option is needed. The unique index itself enforces the constraint, so the operation fails as required when a duplicate sku is present.

• ✗

  db.inventory.updateOne( { sku: "A100" }, { $set: { qty: 5 } }, { upsert: true } )

  Why it's wrong here

  This update with upsert inserts only when no document matches the filter. If a document with sku "A100" already exists, it updates that document instead of failing, which is the opposite of the required behavior. It does not produce a duplicate key error and therefore does not satisfy the scenario.

• ✗

  db.inventory.insertMany( [ { sku: "A100", qty: 5 } ], { bypassDocumentValidation: true } )

  Why it's wrong here

  bypassDocumentValidation skips schema validation rules, not unique index constraints. A duplicate sku would still trigger a duplicate key error, but the option is irrelevant to the requirement and adds unnecessary complexity. It also does not reduce code or improve correctness compared to a plain insertOne.

• ✗

  db.inventory.insertOne( { sku: "A100", qty: 5 }, { ordered: false } )

  Why it's wrong here

  The ordered option controls whether the server stops at the first error when inserting multiple documents. For a single insertOne it has no effect on duplicate detection. The operation would still throw a duplicate key error on a duplicate sku, but the option is unnecessary and does not change the behavior described.