Rails：如何实现一个命名范围，返回至少写入一条消息的所有用户？
考虑以下关联：
class User < ActiveRecord::Base
has_many :messages, :foreign_key => "publisher_id"
scope :wrote_at_least_one_message, <??>
end
class Message < ActiveRecord::Base
belongs_to :publisher, :class_name => "User"
end
如何实现 wrote_at_least_one_message 命名范围？
Consider the following associations:
class User < ActiveRecord::Base
has_many :messages, :foreign_key => "publisher_id"
scope :wrote_at_least_one_message, <??>
end
class Message < ActiveRecord::Base
belongs_to :publisher, :class_name => "User"
end
How could I implement the wrote_at_least_one_message named scope ?
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这个怎么样？内连接将检查消息表中至少一项。区别是为了避免重复。
How about this? The inner join would check for at least one entry in messages table. Distinct is to avoid duplicates.