CODEWITHSUNDEEP
ruby-on-railsrubymongodbruby-on-rails-4mongoid
CJ Jacobs
CJ Jacobs

Reputation: 299

Error counting the number of records with a unique value in a field

I have a field called deviceID and I am trying to get the number of unique values of that field in my database (MongoDB). I was looking at examples in this SO post, yet none of them were working for me. I am using Rails 4.2.2 and I also have these lines of code currently working:

Example 1:

<p id="total">Total number of database entries: <%= DistributedHealth.count %></p>

Example 2:

<% @distributed_healths.each do |distributed_health| %>
  <tr>
    <td><%= distributed_health.deviceID %></td>
  </tr>
<% end %>

These are some of my failed attempts at getting this done.

Failed attempt #1:

<%= DistributedHealth.distinct.count(:deviceID) %>

Error for #1:

wrong number of arguments (0 for 1)

Failed attempt #2:

<%= DistributedHealth.distinct.count('deviceID') %>

Error for #2:

wrong number of arguments (0 for 1)

Failed attempt #3 (I know this is for Rails 3 but I was desperate):

<%= DistributedHealth.count('deviceID', :distinct => true) %>

Error for #3:

wrong number of arguments (2 for 0)

I can post any additional code that would be helpful, any help is greatly appreciated. I will update this post if I get this working. Thank you in advance.

Clayton

EDIT 1:

From my Gemfile:

gem 'mongoid'
gem "moped"
gem 'bson_ext'

SOLUTION:

As was posted below the code I needed was

DistributedHealth.distinct('deviceID').count

Upvotes: 0

Views: 336

Answers (1)

mu is too short
mu is too short

Reputation: 434805

You're almost there:

DistributedHealth.distinct('deviceID').count

You want to grab the distinct deviceIDs using distinct and then count them using Array#count (or Array#length if you want to remind yourself that you're really counting the elements in an array rather than directly querying the database for the count).

Upvotes: 1

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