February 2013
Intermediate to advanced
380 pages
7h 45m
Japanese
Content preview from Nodeクックブック
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126
4 章 データベース接続
db.changes
は変更ログのストリームを受け取るために、内部で
CouchDB
へのリクエスト
URL
に
?feed=continuous
を付与して送信します。リクエストを受け取った
CouchDB
は
cradle
にレス
ポンスを返します。このとき、
changes
メソッドの戻り値の
EventEmitter
（
Node
のコアモジュー
ルで、イベントを発生させるメソッドと待機するメソッドを持った基本クラス）が
response
イベ
ントを発生させます。
response
イベントのコールバック関数に渡される
response
パラメータも
EventEmitter
です。この
EventEmitter
で
data
イベントを待機します。
データベースに変更が発生すると、
data
イベントが発生します。コールバック関数の
change
パ
ラメータに渡された値を処理します。ここで注意したいのは、データベースの変更
1
回につき、
2
つの
data
イベントが発生することです。
1
つは
JSON
文字列、もう
1
つはまったく同じデータを
持った
JavaScript
オブジェクトです。
change
オブジェクトはデータベースエントリのメタデータを保持しています。ドキュメント
ID
（
id
）、連番（
change.seq
）、リビジョン番号（
change.change[0].rev
）です。これらに加えて、削
除済みフラグ（
change.deleted
）が含まれている場合もあります。
ドキュメント
ID
（
change.id
）を
db.get
に渡してドキュメントを取得し、 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
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.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.