如何從Ruby表中返回一個唯一的隨機行？

Question

模型

class Answer < ActiveRecord::Base 
def self.energy(v, w) 
    a = self.where('energy_id = ? AND weight = ?', v, w) 
    a.offset(rand(a.count)).first.name 
end 

視圖

<%= form_for(@answer) do |f| %> 
    <%= f.submit "#{Answer.energy(3, 1)}", name: "answer", class: "btn" %> 
    <%= f.submit "#{Answer.energy(4, 1)}", name: "answer", class: "btn" %> 
<% end %> 

我有，它返回一個隨機值，正常。我打電話給這36次（18對2），而且我不希望相同的價值不止一次地返回。我嘗試了各種.pop變化，但每次都失敗。

感謝您的幫助！

爲號召，我使用這些表單按鈕，所以我去了：

<% names = [] %> 

<div id='one' class='center'> 
    <%= form_for(@answer) do |f| %> 
    <%= f.submit "#{record = Answer.energy(3, 1, names)}", name: "answer", class: "btn btn-large btn-primary" %> 
    <% names << record %> 
    <%= f.submit "#{record = Answer.energy(4, 1, names)}", name: "answer", class: "btn btn-large btn-primary" %> 
    <% names << record %> 
    <% end %> 
</div> 
~~ 17 more times ~~ 

的作品就像一個魅力！謝謝，jvnill，尋求幫助！

Answer 1

你可以使用.order("RAND()")爲mysql，.order("RANDOM()")爲postgre。

UPDATE：no duplicates。

def self.energy(v, w) 
    where('energy_id = ? AND weight = ?', v, w).limit(16).uniq.pluck(:name) 
end 

更新：16次，沒有重複的

它返回匹配的能量和重量，不包括在except_names

# model 
def self.energy(v, w, except_names = []) 
    klass = where('energy_id = ? AND weight = ?', v, w) 
    klass = klass.where('name NOT IN (?)', except_names) if except_names.any? 
    klass.order('RAND()').first.name 
end 

這種調用方法16倍，第隨機記錄，每次向名稱中添加uniq名稱

# how to call 
names = [] 
16.times do 
    if record = Model.energe(1, 1, names) 
    names << record 
    end 
end 

Answer 2

def self.energy(v, w) 
    c = [] 
    a = self.where('energy_id = ? AND weight = ?', v, w) 
    b = a.offset(rand(a.count)).first.name 
    unless c.include?(b) do 
    puts b 
    c << b 
    end 
end 

Answer 3

如果你調用它16次，你可以傳遞已經存在的行作爲參數嗎？如果是，那麼這項工作？

def self.energy(v, w, records = []) 
    a = self.where("energy_id = ? AND weight = ? AND id NOT IN ('-1',?)", v, w, Array(records).map(&:to_param)) 
    a.offset(rand(a.count)).first.name 
end 

用法：

records = [] 
16.times do 
records << Answer.energy(10, 5, records) 
end 

你也可以傳遞一個數組，而不是單個記錄：

other_record = Answer.energy(10,5) 
Answer.energy(10, 5, other_record)