如何更改MongoDB中字段的类型

Question

Here are my questions:

1. How to change all the string type "NULL" in one field to nulls in null type in MongoDB?

2. How to change all the string type "20xx-xx-xx" in one field to date type in MongoDB?

Answer 1

db.foo.insert({bar: "NULL", date: "2012-11-30"})
db.foo.insert({bar: "NULL", date: "2010-09-21"})
db.foo.insert({bar: "NOTNULL", date: "2010-09-21"})

How to change all the string type "NULL" in one field to nulls in null type in MongoDB?

db.foo.update({bar: "NULL"}, {$set: {bar: null}}, {multi: true})

How to change all the string type "20xx-xx-xx" in one field to date type in MongoDB?

db.foo.find({date: {$exists: true}}).forEach(
   function(doc) {doc.date = new Date(doc.date); db.foo.save(doc)}
)

Edit

If for some reason you have problem with default parsing it can be done manually:

Lets assume you have document like this

doc = {date: "2012-01-30"}

First split string representation on hypens and cast each to integer

dateArray = doc.date.split('-').map(function(s) { return parseInt(s); })

Substract 1 from month field (months in js are counted from 0)

dateArray[1] -= 1

Now we can create new date object. There are whoever some things to consider. When you parse string to date, there is assumption that the string represents UTC date when you use this:

new Date("2012-01-30")

You will get

ISODate("2012-01-30T00:00:00Z") 

You can also create Date constructor like this

new Date(dateArray[0], dateArray[1], dateArray[2])

but it will assume that data is using local tz so and in my case (GMT+1) I get:

ISODate("2012-01-29T23:00:00Z")

If it is not what you want you can set some fields manually:

date = new Date(0) // ISODate("1970-01-01T00:00:00Z")
date.setUTCFullYear(dateArray[0], dateArray[1], dateArray[2])

Now date looks like this:

ISODate("2012-01-30T00:00:00Z")

Wrapping it all together:

db.foo.find({date: {$exists: true}}).forEach(
   function(doc) {
       dateArray = doc.date.split('-').map(function(s) { return parseInt(s); });
       dateArray[1] -= 1;

       date = new Date(0);
       date.setUTCFullYear(dateArray[0], dateArray[1], dateArray[2]);

       doc.date = date;
       db.foo.save(doc)
    }
)