Ruby-on-rails Rails .where 与 .find

Rails .where vs .find

提问by AdamB

I've noticed that the Model.wheremethod always returns an array even if there is only one result where as the Model.findmethod doesn't. Is there any reason for this? I thought Model.wherewas the preferred function since Rails 3.X.

我注意到该Model.where方法总是返回一个数组，即使只有一个结果，而该Model.find方法没有。这有什么原因吗？我认为这Model.where是自 Rails 3.X 以来的首选功能。

Should I be using Model.findwhen I expect a single result and Model.wherewhen I expect more than one result?

我应该Model.find在期望单一结果Model.where时还是期望多个结果时使用？

回答by Andrew Marshall

• wherereturns an ActiveRecord::Relation(not an array, even though it behaves much like one), which is a collectionof model objects. If nothing matches the conditions, it simply returns an empty relation.

• find(and its related dynamic find_by_columnnamemethods) returns a singlemodel object. If nothing is found, an ActiveRecord::RecordNotFoundexception is raised (but not with the dynamic find_by_methods).

  While findcan return an Array of records—not a Relation—if given a list of IDs, using whereis preferred since Rails 3. Many similar uses of findare now deprecated or gone entirely.

• where返回一个ActiveRecord::Relation（不是数组，即使它的行为很像一个），它是模型对象的集合。如果没有匹配条件，它只是返回一个空关系。

• find（及其相关的动态find_by_columnname方法）返回单个模型对象。如果未找到任何内容，ActiveRecord::RecordNotFound则会引发异常（但不是使用动态find_by_方法）。

  虽然find可以返回一个记录数组——而不是一个关系——如果给定一个 ID 列表，where从 Rails 3 开始使用是首选。 许多类似的用法find现在已被弃用或完全消失。

So yes, if you only want and expect a single object, using findis easier, as otherwise you must call Model.where.first.

所以是的，如果你只想要一个对象，使用find更容易，否则你必须调用Model.where.first.

Note that old-style hash options to findand many dynamic find_methods are deprecated as of Rails 4.0 (see relevant release notes).

请注意，从 Rails 4.0 开始，旧式哈希选项find和许多动态find_方法已被弃用（请参阅相关发行说明）。

回答by Kamil Lelonek

Actually find_bytakes a model object from whereobtained ActiveRecord::Relation

实际上find_by从where获取的模型对象中获取ActiveRecord::Relation

def find_by(*args)
  where(*args).take
end

Source

来源

回答by iltempo

Model.findis using the primary key column. Therefore there is always exactly one or no result. Use it when you are looking for one specific element identified by it's id.

Model.find正在使用主键列。因此，总是只有一个结果或没有结果。当您在寻找由其 id 标识的特定元素时使用它。