refer to
http://www.cnblogs.com/time-is-life/p/5489770.html
The latitude and longitude of the loc field of the original data structure stores the dimension first, then the precision, and updates it to the first precision and the latter dimension
db.customerLocation.find({"loc.lat": { $exists: true }}).forEach(function (doc) {
var oldlat = doc.loc.lat;
var oldlng = doc.loc.lng;
db.customerLocation.update({_id: doc._id}, { $set: {"loc": {
"lng" : oldlng,
"lat": oldlat
} } });
})