Arel:需要帮助将SQL语句转换为Rails的Arel代码

Question

试图使下面的SQL在Rails查询中工作。

查询：

select addr.*
  from addresses addr
  join users u
    on addr.addressable_type = 'User'
   and addr.addressable_id = u.id
  join customers c 
    on c.id = u.actable_id
   and u.actable_type = 'Customer' 
 where c.account_id = 1
   and c.site_contact = 't'

这是我的Rails代码：

# Inside my account.rb model
def site_addresses
    a = Address.arel_table #Arel::Table.new(:addresses)
    u = User.arel_table #Arel::Table.new(:users)
    c = Customer.arel_table #Arel::Table.new(:customers)

    # trying to debug/test by rendering the sql. Eventually, I want
    # to return a relation array of addresses.
    sql = Address.
      joins(u).
        on(a[:addressable_type].eq("User").and(a[:addressable_id].eq(u[:id]))).
      joins(c).
        on(c[:id].eq(u[:actable_id]).and(u[:actable_type].eq("Customer"))).
     where(c[:account_id].eq(self.id).and(c[:site_contact].eq(true))).to_sql

    raise sql.to_yaml #trying to debug, I'll remove this later
  end
end

我收到了诸如“未知类: Arel::Table”之类的错误。我没有正确地使用Arel，因为SQL代码是有效的(我可以在数据库上运行它很好)

Answer 1

尝试以下几点：

a.join(u).on(a[:addressable_type].eq("User")... # Using the arel_table and "join" instead

我是从文档上得到答案的

users.join(photos).on(users[:id].eq(photos[:user_id]))