Consider the following document from the products collection: What does the following query using $elemMatch return? db.products.find( { product_code: "345678" }, { variations: { $elemMatch: { size…

Question

Exhibit

Options

• AReturns the complete document but retrieves only the size field from the array
• BReturns the document but with only one element in the variations array (corresponding to size L)
• CReturns the complete document since MongoDB does not support partial array retrieval
• DReturns the complete document but retrieves only the size field from the array and also with only

• A
  16% (5)
• B
  75% (24)
• C
  3% (1)
• D
  6% (2)

Explanation

Option B is correct because $elemMatch used in a projection (the second argument to find()) acts as an array filter - it returns the matched document but limits the variations array to only the first element where size equals "L", not the entire array.

Why the distractors are wrong:

• A & D are wrong because $elemMatch in projection returns the entire matching array subdocument (all its fields like size, color, stock, etc.), not just the size field itself - that would require a nested $project with field selection.
• C is simply false - MongoDB has multiple operators for partial array retrieval, including $elemMatch, $slice, and the positional operator ($).

Memory tip: Distinguish $elemMatch by context - in a query filter (first argument), it matches documents where any array element meets all conditions; in a projection (second argument), it trims the returned array down to the first matching element. Think: filter → find the doc; project → trim the array.

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