ActiveRecord中Find与Where区别

最新推荐文章于 2021-03-28 07:27:35 发布

翻译最新推荐文章于 2021-03-28 07:27:35 发布 · 1.5k 阅读

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本文详细介绍了 ActiveRecord 中的查询方法，包括 find、find_by_*、find_all_by_* 和 where 的使用方式及其返回值的区别。通过具体示例展示了每种方法如何执行 SQL 语句并返回不同类型的数据结构。

find：根据id查找，返回一个对象
find_by_*：返回一个对象
find_all_by_*：返回Array
where：返回ActiveRecord::Relation，操作对象时才执行SQL

在下面的示例中你可以清楚地比较各个语句的返回值和SQL

>> Bookmark.find(1)
SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."id" = ? LIMIT 1  [["id", 1]]
#<Bookmark id: 1, name: "baidu", order: 0, url: "http://www.baidu.com">

>> Bookmark.find(1).class
SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."id" = ? LIMIT 1  [["id", 1]]
Bookmark(id: integer, name: string, order: integer, url: string)

>> Bookmark.find_by_order(0).class
SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."order" = 0 LIMIT 1
Bookmark(id: integer, name: string, order: integer, url: string)

>> Bookmark.find_all_by_order(0).class
SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."order" = 0
Array

>> Bookmark.where(:order => 0).class
#不执行SQL
ActiveRecord::Relation

>> Bookmark.where(:order => 0)
SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."order" = 0
[#<Bookmark id: 1, name: "baidu", order: 0, url: "http://www.baidu.com">,
 #<Bookmark id: 2, name: "rubyer", order: 0, url: "http://www.rubyer.me">]

>> Bookmark.where(:order => 0).first.class
SELECT "bookmarks".* FROM "bookmarks" WHERE "bookmarks"."order" = 0 LIMIT 1
Bookmark(id: integer, name: string, order: integer, url: string)