Which of the following commands finds all the documents in the posts collection with post timestamp field as null?

Question

Options

• Adb.posts.find( { post_timestamp: { $fieldtype: null } } )
• Bdb.posts.find( { post_timestamp: { $type: null } } )
• Cdb.posts.find( { post_timestamp : { $type; 10 > > )
• Ddb.posts.find( { post_timestamp: { $fieldtype: 10 } } )

• C
  92% (12)
• D
  8% (1)

Explanation

Option C is correct because MongoDB uses the $type operator to query by BSON data type, and the BSON type code for null is 10 - so the valid query is db.posts.find({ post_timestamp: { $type: 10 } }). The garbled syntax in option C is a formatting artifact; the underlying concept it represents ($type with value 10) is the only valid approach shown.

Why the distractors fail:

• A & D use $fieldtype, which is not a real MongoDB operator - it simply doesn't exist.
• B passes null as the argument to $type ($type: null), but $type expects a BSON type number (or string alias like "null"), not the null value itself.

Memory tip: Think "type TEN for null" - the BSON type table lists null at position 10, so $type: 10 is your null-detector. You can also use the string alias $type: "null" as an alternative, but the numeric code 10 is what exam questions most commonly test.

No community discussion yet for this question.