活动记录 where.not 返回空数组答案

【问题标题】：Active record where.not returns empty array活动记录 where.not 返回空数组
【发布时间】：2017-11-02 17:29:11
【问题描述】：

以下命令

Fight.last.fight_logs.where(item_id: nil)

生成sql：

Fight Load (0.3ms)  SELECT  "fights".* FROM "fights" ORDER BY "fights"."id" DESC LIMIT $1  [["LIMIT", 1]]
FightLog Load (0.2ms)  SELECT  "fight_logs".* FROM "fight_logs" WHERE "fight_logs"."fight_id" = $1 AND "fight_logs"."item_id" IS NULL LIMIT $2  [["fight_id", 27], ["LIMIT", 11]]

然后返回：

#<ActiveRecord::AssociationRelation [#<FightLog id: 30, fight_id: 27, attack: 0, block: 0, item_id: nil, user_id: 1, damage: 11.0, created_at: "2017-11-02 16:20:55", updated_at: "2017-11-02 16:20:57">, #<FightLog id: 31, fight_id: 27, attack: 0, block: 0, item_id: nil, user_id: 20, damage: 3.0, created_at: "2017-11-02 16:20:57", updated_at: "2017-11-02 16:20:57">, #<FightLog id: 33, fight_id: 27, attack: 0, block: 0, item_id: nil, user_id: 1, damage: 1.0, created_at: "2017-11-02 16:21:40", updated_at: "2017-11-02 16:21:40">, #<FightLog id: 32, fight_id: 27, attack: 0, block: 0, item_id: nil, user_id: 20, damage: 7.0, created_at: "2017-11-02 16:21:33", updated_at: "2017-11-02 16:21:40">, #<FightLog id: 34, fight_id: 27, attack: 0, block: 0, item_id: nil, user_id: 1, damage: 12.0, created_at: "2017-11-02 16:21:47", updated_at: "2017-11-02 16:21:48">, #<FightLog id: 35, fight_id: 27, attack: 0, block: 0, item_id: nil, user_id: 20, damage: 14.0, created_at: "2017-11-02 16:21:48", updated_at: "2017-11-02 16:21:48">]>

但是

Fight.last.fight_logs.where.not(item_id: 1)

生成sql：

Fight Load (1.0ms)  SELECT  "fights".* FROM "fights" ORDER BY "fights"."id" DESC LIMIT $1  [["LIMIT", 1]]
FightLog Load (0.8ms)  SELECT  "fight_logs".* FROM "fight_logs" WHERE "fight_logs"."fight_id" = $1 AND ("fight_logs"."item_id" != $2) LIMIT $3  [["fight_id", 27], ["item_id", 1], ["LIMIT", 11]]

然后返回：

#<ActiveRecord::AssociationRelation []>

这怎么可能？我做错了什么？

【问题讨论】：

标签： sql ruby-on-rails activerecord

【解决方案1】：

您应该在查询中指定 NULL 值，因为您的数据库中有它：

Fight.last.fight_logs.where('item_id != ? OR item_id IS NULL', 1)

这正是 SQL 的工作原理：

select 1 != NULL;
+-----------+
| 1 != NULL |
+-----------+
|      NULL |
+-----------+

您可以查看this answer 来澄清问题。另外，我建议避免在数据库中使用默认的 NULL 值，answer 很好。您可以简单地使用default: 0, null: false 您的案例。

【讨论】：

@MrYoshiji You have passed Hash object to #or. Pass an ActiveRecord::Relation object instead
@MrYoshiji 使用 Rails 5
@Src 使用.or(Flight.last.flight_logs.where(item_id: nil))（您可以将此范围存储在变量中）
@MrYoshiji，我更喜欢我目前的答案（IMO 它比这个长范围更干净）。
我同意，但我认为最好展示不同的选项，然后争论哪个更好。