CODEWITHSUNDEEP
ruby-on-railsactiverecordrelationship
Tim Sullivan
Tim Sullivan

Reputation: 16888

Rails counting through relationships

I'm having problems getting my brain around this.

I have four models: Account has many-> List has many-> ListItem <-belongs to Category

I need to get a list of the top-n Categories and the quantity count -- the ones that have the most related ListItems. To make it more complex, the Account has a "role" (say, 'team lead' and 'manager', and the count needs to be separated by that role. To summarize, I need this:

Top 5 Categories for Team Lead: Category122 (74), Category342 (67), Category22 (52), Category992 (50), Category12 (47) 
Top 5 Categories for Manager: Category1 (174), Category32 (112), Category22 (88), Category92 (73), Category5 (72)

I keep trying to form scopes or write class methods to generate these numbers and don't get far before I get confused.

Anyone know how this type of thing can be calculated?

Upvotes: 0

Views: 229

Answers (2)

kwarrick
kwarrick

Reputation: 6190

Add this to your Account model:

has_many :list_items, :through => :lists

Then you can do this:

a = Account.first
a.list_items.joins(:category).group("categories.name").count
# => {"foo"=>1, "bar"=>2}

EDIT

@categories = Category.select("categories.name AS name, accounts.role AS role, count(list_items.id) AS count")
.joins(:list_items => {:list => :account})
.group("categories.name, accounts.role")
.order("count desc")
.limit(5)

@categories[0].role
# => Team Leader
@categories[0].count
# => 5

You'll have to add the category fields to the select, and the query looks something like:

SELECT categories.name, accounts.role, count(list_items.id) 
FROM list_items INNER JOIN lists ON lists.id = list_items.list_id 
INNER JOIN categories ON categories.id = list_items.category_id 
INNER JOIN accounts ON lists.account_id = accounts.id 
GROUP BY categories.name, accounts.role;

Upvotes: 1

David
David

Reputation: 7303

You could try something like this: 

top_team_lead_categories = Category.all(
  :joins => {:list_item => {:list => :account}},
  :select => "categories.*, sum(if(list_items.category_id = categories.id, 1, 0)) as list_items_count",
  :conditions => ['accounts.role =?', 'team lead'],
  :group => 'categories.id',
  :order => 'list_items_count desc'
)

Upvotes: 0

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