Using Mongo Update and $set to insert field (throwing error) - ruby-on-rails-3

Question

Ok, this is probably a stupid question but I have been reading and trying different queries and for some reason I cannot get this to work without throwing an error. This is my first time working with MongoDB and it is in an RoR project. We set up charities to have a twitter handle field, but it was not put into the model originally. So we populated the DB with charities, but now none of them have the twitter handle field. I added it to the model so now all others created will have it.
My issue is when I try to update the charities already in my DB I keep getting an error pointing at $set:
namespace :add_tw_handles_fields_2013_6_13 do
desc "add_tw_handle"
task :add_tw_handle => :environment do |t, args|
# db.charity.update( { featured: false }, { $set: { tw_handle : "test"}}, false, true)
# got your 6
Charity.update({ },
{
$set: { "tw_handle": "test"}
},
{ multi: true }
})
end
end
I tried the 2 synax calls above, I was reading in these 2 docs http://docs.mongodb.org/manual/reference/method/db.collection.update/ http://docs.mongodb.org/manual/core/update/#Updating-The%24positionaloperator.
I always get this error tho:
add_tw_handles_fields_2013_6_13.rake:16: syntax error, unexpected ':', expecting tASSOC
$set: {
As far as I can tell that is the correct syntax. I am running this in the script so I don't think I need the db. before my Model name (as shown in the uncommented update) right? I am new to this, but I literally copied and pasted the example and filled out my info, and nothing. I then tried adding a query, but there is never an error until it gets to $set: and I have no idea why. It is exactly as is shown in the Mongo docs linked above.
Any insight into what my issue would be greatly appreciated.
Thanks,
Alan

Answer 1

The error you're getting is from Ruby, not MongoDB, because you're trying to use MongoDB's JSON syntax inside of Ruby, which Ruby does not like. :) Your update query looks fine but you need to translate it to Ruby syntax which is a bit different.
coll.update( { }, { "$set" => { "tw_handle" => "test" } } );
will work assuming coll is your Collection object.
See here for a good tutorial (written by the MongoDB Ruby team) on using the Ruby driver.

Answer 2

Ok so after looking around and talking to the other dev on this project this is what I have found:
Inside a rails script you want to access the objects through rails not the mongoDB directly:
Following example is for running a script from within lib/tasks
Uses Rails activerecord to update the entry through the framework
m = ModelName.find("51b610972f52760fcc003331")
m.update_attributes( :attribute_name => "what you want to assign" )
m.save
Finds the object that has the id given from your model in rails (accesses mongo db directly)
object = ModelName.find({
"$in" => {
"_id" => "51b610972f52760fcc003331"
}
})
object.first.update_attributes(:attribute_name => "what you want to assign")
From within the console
Within the rails console you can use the first segments syntax using the activerecord models to access the objects you are querying for. But if you want to go directly into the mongo console the syntax is slightly different then above.
after going to the root directory of your project launch mongo in the console and find an object from one of your collections based on its id:
>mongo
>show dbs
>use dbsname
>show collections
>db.collection_name.find({ _id: { $in: [ ObjectId("51b610972f52760fcc003331") ] }})
Hopefully this is helpful to others just learning, syntaxs are different in each. I was told that mongo console runs with javascript, where the rails console (and within the project) is using the activerecord to run the call then manipulate the MongoDB. The commenter above was only addressing accessing the mongoDB directly from within a script. So hopefully this is a little more complete in the different ways you could run into this issue.