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[英]How do I execute a subselect (or large group by) of SQL in Rails 4 with ActiveModel?
[英]rails ActiveModel add attribure that is not persisted
我正在嘗試查詢模型表:
> messages = Message.find_by_sql("select count(*) as messages_count,
> sender_id, recipient_id, min(is_read) as is_read from messages group
> by sender_id, recipient_id")
DB表包含字段sender_id,receiver_id,is_read。 結果,我得到了一個不存在messages_count的哈希數組。
我嘗試過
class Message < ActiveRecord::Base
def attributes
super.merge('messages_count' => self.messages_count)
end
after_initialize do
self.messages_count = nil unless @attributes.key?("messages_count")
end
我也嘗試覆蓋這樣的哈希
def serializable_hash(options = {})
end
這不是觸發的。
我還能嘗試什么? 謝謝!
我在此線程中找到了解決方案。
messages = ActiveRecord::Base.connection
.select_all("select count(*) as messages_count,
sender_id, recipient_id, min(is_read) as is_read
from messages group by sender_id, recipient_id").to_a
返回值:
[{"messages_count"=>3, "sender_id"=>409608538, "recipient_id"=>762146111, "is_read"=>"f"}, {"messages_count"=>1, "sender_id"=>409608538, "recipient_id"=>950961012, "is_read"=>"f"},
{"messages_count"=>2, "sender_id"=>762146111, "recipient_id"=>409608538, "is_read"=>"t"}]
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