How to tell whether a collection exists in MongoDB using Mongoid?

Since Mongoid.master.collection() returns a collection even开发者_StackOverflow中文版 if the collection doesn't exist, we can use

coll = Mongoid.master.collection('analyticsCachedResult')
if coll.count == 0
  # [...]
end

to test if it is an empty collection. Another method is to loop through

Mongoid.master.collections.each do |c|
  return c if c.name == 'analyticsCachedResult'
end
return nil

but is there a simpler way to detect whether it exists?

Not sure how to do it through Mongoid, but in general you can query the system.namespaces collection for {name : "dbname.analyticsCachedResult"}.

Using the mongo ruby driver, I extended the DB class:

class Mongo::DB
  def collection_exists?(collection_name)
    x = "#{self.name}.#{collection_name}" # e.g., "redbike_db.clients"
    nil != self['system.namespaces'].find_one({'name' => x})
  end
end

For the gem mongoid (8.0.2), I use this code

client = Mongoid.default_client
current_db = client.database

current_db.collection_names.include?("name of the collection you want to check")