记录条数:count
和count_by_sql
例如: c1 = Order.count
c2 = Order.count(["name = ?", "Dave Thomas"])
c3 = LineItem.count_by_sql("select count(*) " +
" from line_items, orders " +
" where line_items.order_id = orders.id " +
" and orders.name = 'Dave Thomas' ")
puts "Dave has #{c3} line items in #{c2} orders (#{c1} orders in all)"在
个
中
数据库有可能被多个进程或多个访问随时都有可能获取最新Model对象这些对象有可能刚刚被编辑过从某种程度上讲
这主要应用在事务中不管如何说当你需要手动刷新Model对象时Active Record可以帮助你只需
reload思路方法Model对象属性值就会被数据库中值更新stock = Market.find_by_ticker("RUBY")
loop do
puts "Price = #{stock.price}"
sleep 60
stock.reload
end
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