RuleCategory 有很多规则。我想按 RuleCategories 拥有的规则数量列出它们。
我正在使用 Rails 5.2.1，但是当我执行 group by 并尝试按 count(*) 排序时，我收到一条错误消息，因为我使用的是原始 SQL。
RuleCategory.joins(:rules).where(rules: {edit_status: [Rule::EDIT_STATUS_SYNCHED, Rule::EDIT_STATUS_EDIT]})
.group(:category).order('count(*)').limit(5).pluck(:category, :id).to_a
DEPRECATION WARNING: Dangerous query method (method whose arguments are used as raw SQL)
called with non-attribute argument(s): "count(*)". Non-attribute arguments will be disallowed
in Rails 6.0. This method should not be called with user-provided values,
such as request parameters or model attributes.
Known-safe values can be passed by wrapping them in Arel.sql(). (called from irb_binding at (irb):2)
如何在 order 子句中添加 count …
我在Rails 5中运行以下查询，目的是寻找音高最高的用户：
User
.select("users.*, COUNT(user_id) as pitch_count")
.unscoped
.joins("LEFT JOIN pitches AS pitches ON pitches.user_id = users.id")
.group("pitch.user_id")
.order("pitch_count DESC")
.limit(5)
但是我得到了错误：
Caused by PG::UndefinedColumn: ERROR: column "pitch_count" does not exist
为什么查询不能按pitch_count排序？