我有Category
是has_many
Pendencies
的典范。我想创建一个由具有active = true
不排除active = false
的Pendencies量责令类别的作用域。
我至今是:
scope :order_by_pendencies, -> { left_joins(:pendencies).group(:id).order('COUNT(pendencies.id) DESC')}
这将通过pendencies数量订购它,但我想有active = true
pendencies订购。
另一种尝试是:
scope :order_by_pendencies, -> { left_joins(:pendencies).group(:id).where('pendencies.active = ?', true).order('COUNT(pendencies.id) DESC')}
这将有pendencies.active = true
pendencies数顺序,但会排除pendencies.active = false
。
谢谢您的帮助。
我猜你想主动pendencies的量,而不会忽略不活跃pendencies类别进行排序。
这将是这样的:
scope :order_by_pendencies, -> {
active_count_q = Pendency.
group(:category_id).
where(active: true).
select(:category_id, "COUNT(*) AS count")
joins("LEFT JOIN (#{active_count_q.to_sql}) AS ac ON ac.category_id = id").
order("ac.count DESC")
}
等效SQL查询:
SELECT *, ac.count
FROM categories
LEFT JOIN (
SELECT category_id, COUNT(*) AS count
FROM pendencies
GROUP BY category_id
WHERE active = true
) AS ac ON ac.category_id = id
ORDER BY ac.count DESC
需要注意的是,如果有一个类别没有活跃pendencies,计数会为空,将被添加到列表的末尾。类似的子查询可以被添加到由pendencies总量还排序...
C#的答案的要求:
method() {
....OrderBy((category) => category.Count(pendencies.Where((pendency) => pendency.Active))
}
或直SQL:
SELECT category.id, ..., ActivePendnecies
FROM (SELECT category.id, ..., count(pendency) ActivePendnecies
FROM category
LEFT JOIN pendency ON category.id = pendency.id AND pendnecy.Active = 1
GROUP BY category.id, ...) P
ORDER BY ActivePendnecies;
我们要输出ActivePendnecies
,即使代码将它扔了SQL,因为否则优化是其权利范围内抛出了ORDER BY
。
现在,我制定了以下的(它的工作,但我相信,这是不是最好的方法):
scope :order_by_pendencies, -> { scoped = Category.left_joins(:pendencies)
.group(:id)
.order('COUNT(pendencies.id) DESC')
.where('pendencies.active = ?', true)
all = Category.all
(scoped + all).uniq}