Copying over complete databases is not that hard with mongodb. Use mongodump followed by mongorestore and there you go. But say you want to copy only certain records from certain collections, things get a little bit hairy.

Why? Can't I just use some javascript and the mongo-shell? No. Some mongo commands just don't have authentication, so I found it was the easiest way to use mongorestore and mongodump and wrap them into a handy library.

require 'mongo/util'

# Create mongo util instance, set database to fetch from and database to copy to
# as well as dump folder
mongo = Mongo::Util.new({ host: 'foo.mongohosting.com', port: 31337, db: 'foo' },
                        { db: 'foo_development' },
                        'mongo_dump')

# Add authentication
mongo.from = { user: 'root', password: 'password' }

# Iterate over collections
mongo.collections.each do |collection|

  # Add some case here
  if collection == 'some.collection'

    # Add queries here as you like
    mongo.remove!(collection, query: { something: false })
    mongo.dump(collection: collection, query: { something: false })

  else

    # Just copy
    mongo.remove!(collection)
    mongo.dump(collection: collection)

  end

  # Restore & clean up dump folder
  mongo.restore!
  mongo.clean!                                                                                                   
end

The snippet above is replacing the contents of all collections from localhost:27017/foo_development with the ones from foo.mongohosting.com:31337/foo (you can also specify an external db to copy to, localhost:27017 is standard), except for some.collection, for which it only replaces the entries where the query { something: false } matches.

Install as you would install any other gem. bundler is your friend!

When you're using Rails and you want to use this gem for a script to get fresh production data, just use bundle exec yourscript.rb, where yourscript.rb contains something like above.

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