Ruby on Rails 開發實戰（四十七）：ActiveRecord 基礎 - 強大的 find 方法

find 是 ActiveRecord 查詢的核心，支援豐富選項構建複雜查詢。

基本參數：:first / :all

• find(:first, ...)：回傳單一物件，相當於 LIMIT 1
• find(:all, ...)：回傳陣列

常用選項

分頁範例

def self.find_on_page(page_num, page_size)
  find(:all, :order => "id", :limit => page_size, :offset => page_num * page_size)
end

完整 SQL 控制：find_by_sql

orders = LineItem.find_by_sql(
  "select line_items.* from line_items, orders " +
  "where order_id = orders.id and orders.name = 'Dave Thomas'"
)

回傳模型物件，屬性對應 SELECT 列表。可用 attributes、attribute_names、attribute_present? 檢查載入欄位。

派生欄位與別名

items = LineItem.find_by_sql(
  "select *, quantity*unit_price as total_price, products.title as title " +
  "from line_items, products where line_items.product_id = products.id"
)
li = items[0]
puts "#{li.title}: #{li.quantity}x#{li.unit_price} => #{li.total_price}"

參數化查詢

Order.find_by_sql(["select * from orders where amount > ?", params[:amount]])