db.find({ planet: /ar/ } not work

[weylanshi]

Hi ,when I use find using a regular expression ,is does work ,for the code as follows, it should return Mars and Earth ,but actually return nothing ,is there any problem?

• not work

  // Finding all planets whose name contain the substring 'ar' using a regular expression
  db.find({ planet: /ar/ }, function (err, docs) {
  // docs contains Mars and Earth
  });

• work

  // Finding all planets in the solar system
  db.find({ system: 'solar' }, function (err, docs) {
  // docs is an array containing documents Mars, Earth, Jupiter
  // If no document is found, docs is equal to []
  });