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find_or_initialize_by 和 find_or_create_by

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  • ruby
 
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Hash 和相等性

ActiveRecord 的 hash 值是根据主键的值计算出来的,这就意味着未保存对象的 hash 值是不可靠的。同样两个 model 对象的相等比较(即==操作符)也是基于主键的,所以两个 model 对象即使它们的其他属性不一样,仍有可能被当作相等。

查找

find_by_attribute 方法后面加个 ! 号,即使用 find_by_attribute!,就能在找不到对象的时候触发一个 RecordNotFound 异常,而不是返回 nil。

find_or_initialize_by 和 find_or_create_by 也是两个好用的方法,它们在找不到对象时分别使用 new 和 create 新建一个,并用查找的属性初始化新建的对象。

find_or_initialize_by 和 find_or_create_by 在mongoid 下也是支持的。。
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