How to get list of mongodb databases and collections list from a ruby on rails app

In mongoid 3

Mongoid.default_session.collections # returns the collections

I usually extract the names as follows:

Mongoid.default_session.collections.map(&:name).sort

You can do the following using the mongo ruby driver:

require 'rubygems'
require 'mongo'

connection = Mongo::Connection.new("localhost")
connection.database_names.each do |name|
  db = connection.db(name)
  db.collections.each do |collection|
    puts "#{name} - #{collection.name}"
  end
end

It would be easier to get the Mongo::DB out of the Mongoid config:

db = Mongoid::Config.master
db.collection_names

A short version.

db = Mongoid.master
db.collection_names

I used following code to list all collection and fields, provided the list of mongo db databases mentioned in mongoid.yml

def printDb(dbUri)
    puts "#{dbUri}"
    client = Mongo::Client.new(dbUri)
    # List all collections in the current database
    #collections = client.database.list_collections.map(&:name)
    collections = client.database.list_collections
    # Print the collection names
    collections.each do |collection|
            begin
                puts "  collection- #{collection[:name]}"
                colln=client[ collection[:name] ]
                #fields = collection.find_one.keys
                #fields = collection.find.limit(1).keys
                fields = colln.find.first.keys
            puts "      Fields: #{fields}"
            puts "" 
        rescue
            puts "      ** error in looking for a collection **"
            puts "" 
        end
    end
end

uriList=['mongodb://127.0.0.1:27017/my_app_db1',
    'mongodb://127.0.0.1:27017/my_app_db2', 
    'mongodb://127.0.0.1:27017/my_app_db3', 
    'mongodb://127.0.0.1:27017/my_app_db4'
     ]

#call function 
uriList.each do |myUri|
    printDb(myUri)
end

The parts of URI can be changed as per your yml file configurations. It may require mongo and mongoid gems