You have the following index on the toys collection: { "manufacturer" : 1, "name" : 1, "date" : -1 } Which of the following is able to use the index for the query? Check all that apply.

Question

Options

• Adb.toys.find( { name : "Big Rig Truck", date : "2013-02-01", manufacturer : "Tanko"
• Bdb.toys.find( { manufacturer : "Matteo", name : "Barbara", date : "2014-07-02" } )
• Cdb.toys.find( { date : "2015-03-01", manufacturer : "Loggo", name : "Brick Set" } )

Explanation

All three options - A, B, and C - can use the index.

MongoDB's query planner does not care about the order in which fields appear in the find() predicate; it cares whether the queried fields match a left-prefix of the compound index. Here, the index prefix chain is manufacturer → manufacturer, name → manufacturer, name, date. All three queries supply values for all three indexed fields (manufacturer, name, and date), so all three fully match the index regardless of how the fields are ordered inside the {} braces. There are no distractors here - this is a question specifically designed to test whether you mistakenly believe field order in the query document must match field order in the index definition.

Memory tip: Think of a compound index like a phone book sorted by Last Name → First Name → Street. You can look someone up by last name alone, last+first, or all three - but the page you write the search query on doesn't need to list them in that exact order; the index structure itself enforces the sort order.

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