$not

Syntax: { field: { $not: { <operator-expression> } } }

$not performs a logical NOT operation on the specified <operator-expression> and selects the documents that do not match the <operator-expression>. This includes documents that do not contain the field.

Consider the following query:

db.inventory.find( { price: { $not: { $gt: 1.99 } } } )

This query will select all documents in the inventory collection where:

• the price field value is less than or equal to 1.99 or
• the price field does not exist

{ $not: { $gt: 1.99 } } is different from the $lte operator. { $lt: 1.99 } returns only the documents where price field exists and its value is less than or equal to 1.99.

Remember that the $not operator only affects other operators and cannot check fields and documents independently. So, use the $not operator for logical disjunctions and the $ne operator to test the contents of fields directly.

Consider the following behaviors when using the $not operator:

• The operation of the $not operator is consistent with the behavior of other operators but may yield unexpected results with some data types like arrays.

• The $not operator does not support operations with the $regex operator. Instead use // or in your driver interfaces, use your language’s regular expression capability to create regular expression objects.

  Consider the following example which uses the pattern match expression //:

  db.inventory.find( { item: { $not: /^p.*/ } } )
  

  The query will select all documents in the inventory collection where the item field value does not start with the letter p.

  If using PyMongo’s re.compile(), you can write the above query as:

  import re
  for noMatch in db.inventory.find( { "item": { "$not": re.compile("^p.*") } } ):
      print noMatch