You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
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// Match documents that contains that specified field
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db.books.find( {category: {$exists: true }})
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// Match documents whose field value is of the specified BSON data type
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db.books.find( {category: {$type: 2 }})
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