Active Record query to find parents with child within a date range and child prior to that date range

问题

I need an active record query that returns the count of Parents with a Child created within a date range AND a Child created prior to the date range.

I currently have the following two queries: This query returns the count of Parents with a Child created within the date range

Parent.joins(:children).where("children.created_at BETWEEN ? AND ?", start, end).distinct.count(parent_id)

This query counts the Parents with a Child created before the date range

Parent.joins(:children).where("children.created_at < ?", start).distinct.count(:parent_id)

I need to find the count of Parents that have a Child created within the range AND a Child created before the range.

How is the best way to get this result?

回答1:

You can do this in following ways,

Simple way, get the ids for parent from the first query and apply the filter on parent id in second query,

 q1_pids = Parent.joins(:children)
                 .where("children.created_at BETWEEN ? AND ?", start, end)
                 .ids
 count = Parent.joins(:children)
               .where("children.created_at < ?", start)
               .where(id: q1_pids)
               .count("parents.id")

Using INTERSECT

q1 = Parent.joins(:children)
           .where("children.created_at BETWEEN ? AND ?", start, end)

q2 = Parent.joins(:children)
           .where("children.created_at < ?", start)

count = (q1 & q1).count

Second solution just uses array intersection, however you can prepare the SQL statement yourself to fire a single SQL query to the database.

回答2:

Extending @Sujan's answer, you can fetch all the records in a single query as well.

Parent.joins(:children)
      .joins('INNER JOIN children AS before_start_children ON before_start_children.parent_id = parents.id')
      .where(children: {created_at: start..end})
      .where("before_start_children.created_at < ?", start)
      .distinct
      .count(parent_id)

来源：https://stackoverflow.com/questions/58308005/active-record-query-to-find-parents-with-child-within-a-date-range-and-child-pri

标签

ruby-on-rails

activerecord