Question

我有两个模型，Users和Leads与HABTM关系相关：

class Lead < ActiveRecord::Base
  has_and_belongs_to_many :users
end

class User < ActiveRecord::Base
  has_and_belongs_to_many :leads
end

我现在如何才能获得那些未与用户连接的潜在顾客？

提前致谢！

Answer 1

您正在寻找的内容称为 anti join 。

有三种标准方法可以实现这一目标，

使用null左外连接
将where子句与带有NOT＆amp;的子查询一起使用IN个关键字
将where子句与NOT＆amp; EXISTS个关键字

基本上，EXISTS关键字将检查子查询是否返回任何行并报告为匹配，NOT显然否定了该匹配。

这是我的首选方式（使用NOT＆amp; EXISTS）

class User < ActiveRecord::Base
  has_and_belongs_to_many :leads
  def self.without_leads
    where(<<-SQL)
      NOT EXISTS (SELECT 1 
        FROM   leads_users 
        WHERE  users.id = leads_users.user_id) 
    SQL
  end
end

class Lead < ActiveRecord::Base
  has_and_belongs_to_many :users
  def self.without_users
    where(<<-SQL)
      NOT EXISTS (SELECT 1 
        FROM   leads_users 
        WHERE  leads.id = leads_users.lead_id) 
    SQL
  end

 def self.not_connected_to(user)
    where(<<-SQL, user.id)
      NOT EXISTS (SELECT 1 
        FROM   leads_users 
        WHERE  leads.id = leads_users.lead_id
        AND leads_users.user_id = ?
        ) 
    SQL
  end
end

这是使用arel

非SQL

class User < ActiveRecord::Base
  has_and_belongs_to_many :leads
  def self.without_leads
    habtm_table = Arel::Table.new(:leads_users)
    join_table_with_condition = habtm_table.project(habtm_table[:user_id])
    where(User.arel_table[:id].not_in(join_table_with_condition))
  end
end

class Lead < ActiveRecord::Base
  has_and_belongs_to_many :users
  def self.without_users
    habtm_table = Arel::Table.new(:leads_users)
    join_table_with_condition = habtm_table.project(habtm_table[:lead_id])
    where(Lead.arel_table[:id].not_in(join_table_with_condition))
  end
end

here is an example repo

查找没有潜在客户的用户

User.where(user_id: 1).without_leads

查找没有用户的潜在客户

Lead.without_users

查找未与特定用户相关的潜在客户

Lead.not_connected_to(user)

链式排序

Lead.without_users.order(:created_at)

Answer 2

您可以使用左连接。假设您的联接表名为leads_users：

Lead.joins('LEFT JOIN leads_users ON leads_users.lead_id = leads.id').
     where(leads_users: { user_id: nil })

Answer 3

Kerozu，如果要显示仅不是当前用户购买的销售线索，则可以使用这样的原始sql

    sql = <<-SQL
      SELECT *
      FROM leads
      WHERE id NOT IN (
        SELECT lead_id
        FROM leads_users
        WHERE user_id = ?
      )
    SQL

    Lead.find_by_sql [sql, id]

Rails：在HABTM关系中查找没有连接的行

3 个答案: