Ruby on Rails中是否存在检查行(Check row exist or not in Ruby on Rails)

 我是Ruby on Rails的新手，我对mysql有基本的了解。 我正在使用MySQL db。 我的问题是 - 如何检查表中是否存在行。 我已经尝试过这段代码，但它不会直接进入else块，而不是if块： 
 
@tasks = User.find_by("user_name = ? AND password = ?", params[:user_name], params[:password])
if @tasks
  redirect_to action: 'index', status: 302
else
  redirect_to action: 'detail', status: 302
end

I am new to Ruby on Rails and I have basic knowledge of mysql. I am using MySQL db. My question is -- how to check if a row is exists or not in a table. I have tried this code but it's not going straight to the else block, not the if block:
 
@tasks = User.find_by("user_name = ? AND password = ?", params[:user_name], params[:password])
if @tasks
  redirect_to action: 'index', status: 302
else
  redirect_to action: 'detail', status: 302
end

原文：https://stackoverflow.com/questions/22928038