update and set field if it's blank or not set

[rl]

I have an update that sets a few fields on several hundred records (out of millions) based on some criteria.  However, there is one field that I want to only set if it's not set.  e.g.  I have a URL field.  If there is no URL, I want to force it to be "http://www.mycompany.com" but if that field already has a value, I want to keep it.  I need an example of how to do this.

Thanks in advance!

[H.J]

eg:

db.t8.insert({"_id":1,"other":"apple","url":"http://www.mongodb.org"})
db.t8.insert({"_id":2,"other":"apple","url":null})
db.t8.insert({"_id":3,"other":"apple","other":"apple"})

If in all doc there are the 'url' field then you can use:

db.t8.update({$or:[{"url":null},{"url":{$exists:false}}]},
{$set:{"url":"http://www.mycompany.com"}})

if in some doc this field doesn't exist, then you can use:

db.t8.find({$or:[{"url":null},{"url":{$exists:false}}]}).forEach(function(doc){
doc.url = "http://www.mycompany.com";
db.t8.save(doc);
})

Hope this help.

2012/3/29 rl <rob...@cloud2market.com>:

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