Consider the following document: > db.c.find() { "_id" : 12, b : [ 3, 5, 7, 2, 1, -4, 3, 12 ] } Which of the following queries on the "c" collection will return only the first five elements of the…

Question

Options

• Adb.c.find( { > , { b : { $slice : [ 0 , 5 ] } } )
• Bdb.c.find( { b : [ 0 , 5 ] > )
• Cdb.c.find( { > , { b : { $substr[ 0 , 5 ] > > )
• Ddb.c.find( { > , { b : [ 0, 1, 2, 3, 4, 5 ] > )
• Edb.c.find( { > , { b : [ 0 , 5 ] > )

• A
  77% (36)
• B
  15% (7)
• C
  6% (3)
• D
  2% (1)

Explanation

Option A is correct because MongoDB's $slice projection operator is specifically designed to limit array elements returned in query results - $slice: [0, 5] means "skip 0 elements, return 5," yielding [3, 5, 7, 2, 1] exactly as required.

Why the distractors fail:

• B places [0, 5] in the filter (match) position, which tries to match documents where b equals the array [0, 5] - it won't match anything and has no projection.
• C uses $substr, which is a string operator, not an array operator - it doesn't exist in the context of array projection.
• D uses a raw array [0, 1, 2, 3, 4, 5] in the projection, which is not valid MongoDB syntax for slicing.
• E is similar to B's mistake - [0, 5] in the projection field value is not a recognized operator, so MongoDB won't know what to do with it.

Memory tip: Think of $slice like slicing bread - it's always paired with the $ sign (a projection operator), takes the form $slice: [skip, limit], and lives in the second argument (the projection document) of find(), never in the filter.

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