Active Record querying with joins and group by - ruby-on-rails

Question

I'm designing an API to get data from the following scenario :
brands table :
+------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
+------------+--------------+------+-----+---------+----------------+
items table :
+---------------------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------------------+--------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| category_id | bigint(20) | YES | MUL | NULL | |
| brand_id | bigint(20) | YES | | NULL | |
+---------------------------+--------------+------+-----+---------+----------------+
item_skus table :
+---------------------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------------------+--------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| item_id | bigint(20) | YES | MUL | NULL | |
| number_of_stock | int(11) | YES | | NULL | |
+---------------------------+--------------+------+-----+---------+----------------+
Item model association with ItemSku and Brand
belongs_to :brand
has_many :skus, class_name: 'ItemSku'
Simply i want the counts of stock available items and all items for each brand.
{
"brandCounts":[
{
"id":7006,
"name":"Brand 01",
"stockAvailableItemCount":50,
"allItemCount":60
},
{
"id":20197,
"name":"Brand 02"
"availableItemCount":150,
"allItemCount":660
}
]
}
Implementation :
brand_counts = []
brand_counts_hash = Hash.new()
items = Item.left_outer_joins(:skus).where(category_id: params[:id]).pluck(:brand_id, :number_of_stock, :item_id)
items.each do |item|
brand_id = item[0]
stock = item[1]
if brand_counts_hash.has_key?(brand_id)
item_count_arry = brand_counts_hash[brand_id]
stock_available_item_count = item_count_arry[0]
all_item_count = item_count_arry[1]
if stock > 0
brand_counts_hash[brand_id] = [stock_available_item_count + 1, all_item_count + 1]
else
brand_counts_hash[brand_id] = [stock_available_item_count, all_item_count + 1]
end
else
stock_available_item_count = 0
all_item_count = 0
if stock > 0
stock_available_item_count += 1
all_item_count += 1
brand_counts_hash[brand_id] = [stock_available_item_count, all_item_count]
else
all_item_count += 1
brand_counts_hash[brand_id] = [stock_available_item_count, all_item_count]
end
end
end
brand_counts_hash.each do |key, value|
stock_available_item_count = value[0]
all_item_count = value[1]
brand_counts << {
id: key,
name: get_brand_name(key),
stock_available_item_count: stock_available_item_count,
all_item_count: all_item_count
}
end
#brand_counts = brand_counts
render 'brands/counts/index', formats: :json
end
def get_brand_name(brand_id)
brand = Brand.find_by(id: brand_id)
brand.name unless brand == nil
end
Is there a way to optimize this further without multiple loops maybe?

Answer 1

Assume your Brand model also has the following association defined
has_many :items
and the final result you want is like
{
"brandCounts":[
{
"id":7006,
"name":"Brand 01",
"stockAvailableItemCount":50,
"allItemCount":60
},
{
"id":20197,
"name":"Brand 02"
"availableItemCount":150,
"allItemCount":660
}
]
}
The following code may not work when you copy and paste to your project. But it demonstrate how this problem can be solved with less code
Brand.includes(items: :skus).all.map do |brand|
{
id: brand.id,
name: brand.name,
stockAvailableItemCount: brand.items.count,
allItemCount: brand.items.map {|item| item.skus.sum(:number_of_stock)}.sum
}
end
if you need json format, just use to_json to the result of above code.