使用同一张表时，has_many through 不起作用

Question

我有一个模特FamilyService。在模型中，我有这些关联：

belongs_to :family
has_many :balance_histories, :through => :family
has_many :balances, :through => :family

执行此命令：FamilyService.where("families.id > 90000").joins(:balances) 工作正常。我明白了：

SELECT families_services.*
FROM families_services
INNER JOIN families ON families.id = families_services.family_id
INNER JOIN balances ON balances.family_id = families.id
WHERE (families.id > 90000)

另外，执行这个查询：FamilyService.where("families.id > 90000").joins(:balance_histories) 给了我这个：

SELECT families_services.*
FROM families_services
INNER JOIN families ON families.id = families_services.family_id
INNER JOIN balance_histories ON balance_histories.family_id = families.id
WHERE (families.id > 90000)

太棒了！

但是当尝试这样做时：FamilyService.where("families.id > 90000").joins(:balances, :balance_histories)。我明白了：

SELECT families_services.*
FROM families_services
INNER JOIN families ON families.id = families_services.family_id
INNER JOIN balances ON balances.family_id = families.id
INNER JOIN families families_families_services_join ON families_families_services_join.id = families_services.family_id
INNER JOIN balance_histories ON balance_histories.family_id = families_families_services_join.id
WHERE (families.id > 90000)

这是错误的（家庭family_families_services_join ONfamily_families_services_join.id）。 如何解决？

Answer 1

生成的查询实际上是正确的。线

INNER JOIN families families_families_services_join ON ...

只是暂时将名称 families_families_services_join 分配给表 families，以便查询更清晰。

但是，您可以通过将 joins 查询指定为来简化查询，

FamilyService.where("families.id > 90000").joins(family: [:balances, :balance_histories])

这会产生类似的东西

SELECT families_services.*
FROM families_services
INNER JOIN families ON families.id = families_services.family_id
INNER JOIN balances ON balances.family_id = families.id
INNER JOIN balance_histories ON balance_histories.family_id = families.id
WHERE (families.id > 90000)