Question

当我想查找分配了特定方案的特定页面时（通过scheme_assignment），我有一些SQL工作正在运行：

Page.find_by_sql("
    SELECT pages.id
    FROM pages
    INNER JOIN scheme_assignments ON (scheme_assignments.schemable_type = 'Page' AND
                                      scheme_assignments.schemable_id = pages.sid)
    INNER JOIN schemes ON (schemes.sid = scheme_assignments.scheme_id AND
                           schemes.sid IN (4,6,7))
    GROUP BY pages.id")

当我尝试将其转换为ARel时：

Page.select("pages.id")
    .joins("scheme_assignments")
    .on("scheme_assignments.schemable_type = 'Page' AND scheme_assignments.schemable_id = pages.sid")
    .joins("schemes")
    .on("schemes.sid = scheme_assignments.scheme_id AND schemes.sid IN (1)")
    .group("pages.id")

我会收到此错误：NoMethodError: undefined method join_sql'for“schemes”：String`

为什么？是因为它不是我Page模型中的关联吗？可以在没有在模型中创建关联的情况下将该SQL转换为ARel吗？

Answer 1

Page.joins("INNER JOIN scheme_assignments 
        ON (scheme_assignments.schemable_type = 'Page' AND scheme_assignments.schemable_id = pages.sid) 
        INNER JOIN schemes 
        ON (schemes.sid = scheme_assignments.scheme_id AND schemes.sid IN (4,6,7))").
    select("DISTINCT pages.*");

Answer 2

Rails Guides

当您建立关联时，Rails知道要使用哪种联接。我认为（虽然没试过）它应该这样工作：

Page.select("pages.id").joins("INNER JOIN scheme_assignments ON (scheme_assignments.schemable_type = 'Page' AND scheme_assignments.schemable_id = pages.sid)")...

你能加入另一个不是ARel协会的桌子吗？

2 个答案: