MongoDB - Dynamically update an object in nested array

Question

I have a document like this:

{
  Name : val
  AnArray : [
     { 
        Time : SomeTime
     },
     {
        Time : AnotherTime
     }
     ...arbitrary more elements
}

I need to update "Time" to a Date type (right now it is string)

I would like to do something psudo like:

foreach record in document.AnArray { record.Time = new Date(record.Time) }

I've read the documentation on $ and "dot" notation as well as a several similar questions here, I tried this code:

db.collection.update({_id:doc._id},{$set : {AnArray.$.Time : new Date(AnArray.$.Time)}});

And hoping that $ would iterate the indexes of the "AnArray" property as I don't know for each record the length of it. But am getting the error:

SyntaxError: missing : after property id (shell):1

How can I perform an update on each member of the arrays nested values with a dynamic value?

mnemosyn · Accepted Answer · 2013-06-05 12:41:54Z

3

There's no direct way to do that, because MongoDB doesn't support an update-expression that references the document. Moreover, the $ operator only applies to the first match, so you'd have to perform this as long as there are still fields where AnArray.Time is of $type string.

You can, however, perform that update client side, in your favorite language or in the mongo console using JavaScript:

db.collection.find({}).forEach(function (doc) {
       for(var i in doc.AnArray)
       {
          doc.AnArray[i].Time = new Date(doc.AnArray[i].Time);
       }
       db.outcollection.save(doc); 
})

Note that this will store the migrated data in a different collection. You can also update the collection in-place by replacing outcollection with collection.

answered Jun 5, 2013 at 12:41

mnemosyn

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2 Comments

Avba Over a year ago

Can I just call ISODate("My iso Date string") and set it to the time variable? Look good in the console but not sure it will use it as a true "Date" type

mnemosyn Over a year ago

yes, that's ok. Actually, I expected the string to be in that (ISO 8601) format. The string you posted looks fine, works with the script on my machine, MongoDB 2.5.0

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