Rails:加入多个条件 [英] Rails: join with multiple conditions

问题描述

我有一个简单的模型，比如

I have a simple model like

class Interest < ActiveRecord::Base
  has_and_belongs_to_many :user_profiles
end

class UserProfile < ActiveRecord::Base
  has_and_belongs_to_many :interests
end

当我想查询具有特定兴趣的所有用户时，这很简单

When I want to query all the users with a specific interests, that's fairly simple doing

UserProfile.joins(:interests).where('interests.id = ?', an_interest)

但是我如何寻找具有多种兴趣的用户?当然如果我这样做

But how can I look for users who have multiple interests? Of course if I do

UserProfile.joins(:interests).where('interests.id = ?', an_interest).where('interests.id = ?', another_interest)

我总是得到一个空结果，因为在加入之后，没有行可以同时具有interest.id = an_interest 和interest.id = another_interest.

I get always an empty result, since after the join, no row can have simultaneously interest.id = an_interest and interest.id = another_interest.

ActiveRecord 中有没有办法表达我想要有 2 个(指定的)兴趣相关联的用户列表?

Is there a way in ActiveRecord to express "I want the list of users who have 2 (specified) interests associated?

更新(解决方案)这是我提出的第一个工作版本，感谢 Omar Qureshi

update (solution) that's the first working version I came up, kudos to Omar Qureshi

    specified_interests.each_with_index do |i, idx|
      main_join_clause = "interests_#{idx}.user_profile_id = user_profiles.id"
      join_clause = sanitize_sql_array ["inner join interests_user_profiles interests_#{idx} on
                    (#{main_join_clause} and interests_#{idx}.interest_id = ?)", i]

      relation = relation.joins(join_clause)
    end

推荐答案

in (?) 不好 - 它是一个类似 OR 的表达式

in (?) is no good - it's an OR like expression

您需要做的是手写多个连接

what you will need to do is have multiple joins written out longhanded

profiles = UserProfile
interest_ids.each_with_index do |i, idx|
  main_join_clause = "interests_#{idx}.user_profile_id = user_profiles.id"
  join_clause = sanitize_sql_array ["inner join interests interests_#{idx} on
                        (#{main_join_clause} and interests_#{idx}.id = ?)", i]
  profiles = profiles.join(join_clause)
end
profiles

您可能需要更改 main_join_clause 以满足您的需要.

You may need to change the main_join_clause to suit your needs.

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