的Rails 3：從數據庫

我有這些模型刪除重複的關聯：的Rails 3：從數據庫

class Relationship < ActiveRecord::Base 
    belongs_to :student 
    belongs_to :guardian 
end 

class Student < ActiveRecord::Base 
    has_many :relationships 
    has_many :guardians, through: :relationships 
end 

class Guardian < ActiveRecord::Base 
    has_many :relationships 
    has_many :students, through: :relationships 
end

我不希望任何監護人與一名學生有關的許多倍。這可以通過驗證來防止，但讓我們說已經太晚了，並且有時會發生這種情況。例如，在g是監護人：

g.relationships 

[ 
    [0] #<Relationship:0x0000000bc33650> { 
          :id => 40321, 
     :relationship_type_id => 2, 
        :student_id => 41700, 
       :guardian_id => 45820, 
        :created_at => Tue, 23 Apr 2013 17:44:29 UTC +00:00, 
        :updated_at => Tue, 23 Apr 2013 17:44:29 UTC +00:00, 
    }, 
    [1] #<Relationship:0x0000000bc32e80> { 
          :id => 40923, 
     :relationship_type_id => 2, 
        :student_id => 41700, 
       :guardian_id => 45820, 
        :created_at => Tue, 23 Apr 2013 18:58:46 UTC +00:00, 
        :updated_at => Tue, 23 Apr 2013 18:58:46 UTC +00:00, 
    } 
]

正如你可以看到，這兩個關係共享相同的student_id數據。我想知道是否有辦法從數據庫中刪除重複的關係。我試過以下幾行代碼無濟於事：

g.relationships.uniq!(&:student_id) 
g.update_attributes(relatioships: g.relationships.uniq!(&:student_id))

我該如何解決這個問題。謝謝！

來源

2013-04-25 sauronnikko

是否有任何規則應該保留哪些副本應該保留（最近的，最早的，其他的），或者它並不重要？另外，你想要SQL或Ruby代碼呢？ – PinnyM 2013-04-25 17:05:01

沒有規則，如果有兩種相同的類型，他們中的任何一個都適合我 – sauronnikko 2013-04-25 17:06:06

subquery = Relationship.select("student_id, guardian_id"). 
      group(:student_id, :guardian_id). 
      having("count(*) > 1").to_sql 
groups = Relationship.joins("JOIN (#{subquery}) sub ON relationships.student_id = sub.student_id AND relationships.guardian_id = sub.guardian_id"). 
         group_by{|r| [r.student_id, r.guardian_id] } 

groups.values.each do |duplicates| 
    duplicates.drop(1).each(&:destroy) 
end

來源

2013-04-25 17:19:28 PinnyM

的Rails 3：從數據庫

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