April 2022
Beginner to intermediate
464 pages
6h 44m
Japanese
Content preview from 実用 Go言語 ―システム開発の現場で知っておきたいアドバイス
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9.4 クエリーをキャンセルする
「Webアプリケーションで一定時間内にレスポンスを返せなかった」「長い時間のかかるバッチ処理用のクエリーを発行したが処理が終わらない」など、クエリーをキャンセルしたい場面がいくつかあります。クエリーをキャンセルするには、コンテキストを使うのが一般的です。
9.4.1 コンテキスト付きのdatabase/sql関数を使用する
Go 1.8 から database/sql パッケージがコンテキストに対応しました。クエリーをタイムアウトしてキャンセルしたい場合などは、 context.WithCancel() や context.WithTimeout() を使用してキャンセルするのが良いでしょう。ただし使用しているデータベースのドライバーがクエリーのキャンセルをサポートしている必要があります。
クエリーのキャンセルを試みるときは、使用しているデータベースドライバーがキャンセルをサポートしているか確認が必要です。
たとえば一昔に主流だったPostgreSQLドライバーである lib/pg では、クエリーがキャンセルできない、という以下のようなIssueがあります。
リスト9-9:
context.WithTimeout でクエリーをキャンセル ctx, cancel := context.WithTimeout(context.Background(), 5Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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