如何从Ruby表中返回一个唯一的随机行？

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 

视图

<%= 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，它返回一个随机值，正常。我打电话给这36次（18对2），而且我不希望相同的价值不止一次地返回。我尝试了各种.pop变化，但每次都失败。

感谢您的帮助！

为号召，我使用这些表单按钮，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 ~~ 

的作品就像一个魅力！谢谢，jvnill，寻求帮助！

Answer 1

你可以使用.order("RAND()")为mysql，.order("RANDOM()")为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，没有重复的

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 

这种调用方法16倍，第随机记录，每次向名称中添加uniq名称

# 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

如果你调用它16次，你可以传递已经存在的行作为参数吗？如果是，那么这项工作？

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 

你也可以传递一个数组，而不是单个记录：

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