回答編集履歴
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追記
answer
CHANGED
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@@ -69,4 +69,24 @@
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69
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| 6 | 3 | 4 | 200 | beaf_b | 2017-11-19 02:01:31 UTC | 2017-11-19 02:01:31 UTC |
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+----+----------+--------+-------+--------+-------------------------+-------------------------+
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6 rows in set
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72
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```
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追記： 2017-11-19 11:30
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75
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User に has_many :order_details, through: :orders を追加して、
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user.irder_detail をつかった場合は次のようになります。
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(SQL として 2 つの SELECT が発行されています。 joins を使った場合は 1 つの SELECT でした。)
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```ruby
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irb(main):003:0> User.find_by(name: 'kato').order_details
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User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."name" = ? LIMIT ? [["name", "kato"], ["LIMIT", 1]]
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OrderDetail Load (0.3ms) SELECT "order_details".* FROM "order_details" INNER JOIN "orders" ON "order_details"."order_id" = "orders"."id" WHERE "orders"."user_id" = ? [["user_id", 1]]
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+----+----------+--------+-------+--------+-------------------------+-------------------------+
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| id | order_id | amount | price | item | created_at | updated_at |
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+----+----------+--------+-------+--------+-------------------------+-------------------------+
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| 1 | 1 | 1 | 100 | fish_a | 2017-11-19 02:01:31 UTC | 2017-11-19 02:01:31 UTC |
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| 2 | 1 | 2 | 200 | fish_b | 2017-11-19 02:01:31 UTC | 2017-11-19 02:01:31 UTC |
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| 3 | 2 | 1 | 10 | fish_a | 2017-11-19 02:01:31 UTC | 2017-11-19 02:01:31 UTC |
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| 4 | 2 | 2 | 20 | fish_b | 2017-11-19 02:01:31 UTC | 2017-11-19 02:01:31 UTC |
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+----+----------+--------+-------+--------+-------------------------+-------------------------+
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4 rows in set
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72
92
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```
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