Given a collection posts as shown below having a document array comments, which of the following command will create an index on the comment author descending?

Question

Exhibit

Options

• Adb.posts.createIndex({^comments.$.author":-l});
• Bdb. posts.createIndex({^comments.author" :1});
• Cdb.posts.createIndex({^commerits.author";-!});

• A
  6% (2)
• B
  9% (3)
• C
  85% (29)

Explanation

Option C is correct because it uses MongoDB's dot notation ("comments.author") to reference a field inside an embedded array, paired with -1 to specify a descending index - this is the standard syntax for indexing fields in subdocuments/arrays.

Option A is wrong for two reasons: it incorrectly uses the $ positional operator (comments.$.author), which is only valid in update/query operations, not index creation, and it uses -1 with the wrong operator structure.

Option B is wrong because it specifies 1 instead of -1, which creates an ascending index - the question explicitly asks for descending.

Memory tip: Think of MongoDB index direction like a number line - 1 = ascending (positive direction, low to high), -1 = descending (negative direction, high to low). For nested/array fields, always use dot notation ("array.field") with no $ operators, just like you would in a query projection.

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