Consider the following posts document: Which of the following queries will return the documents but with only the first two tags in the tags array?

Question

Exhibit

Options

• Adb.posts.find({author:"Tom"».limit({tags:2})
• Bdb.posts.find({author:"Tom"».limit($slice:{tags:2>)
• Ddb.posts.find({author:"Tom">,{tags:{$slice:2»)

• A
  16% (8)
• B
  8% (4)
• D
  76% (37)

Explanation

Option D is correct because $slice is a projection operator used in the second argument of find() to limit the number of array elements returned - {tags:{$slice:2}} tells MongoDB to return only the first two elements of the tags array. Option A misuses .limit(), which is a cursor method that restricts the number of documents returned, not array elements, and passes it a field-count object which is invalid syntax. Option B makes the same conceptual mistake by trying to pass $slice inside .limit(), which has no understanding of $slice whatsoever. A helpful memory tip: think of the two arguments to find() as filter, then fields - the first {} selects which documents, the second {} controls which fields and how much of them, and $slice lives in that second "how much" argument alongside other projection operators.

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