Ruby-on-rails 在控制台中找到 rails ActiveRecord
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rails ActiveRecord find in console
提问by user740970
When I'm in the Rails 3.2 console, I can do this just fine:
当我在 Rails 3.2 控制台中时，我可以很好地做到这一点：
p = Person.last
p.last_name
and it prints the last name.
并打印姓氏。
But when I try to find it by the id, it's able to locate the single
record and store it in my variable p, but I can't print the last_namecolumn. For example:
但是当我尝试通过 找到它时id，它能够找到单个记录并将其存储在我的变量中p，但是我无法打印该last_name列。例如：
p = Person.where(id: 34).limit(1)
printing phere shows all the columns but p.last_namesays this
p此处打印显示所有列，但这样p.last_name说
NoMethodError: undefined method `last_name' for
#<ActiveRecord::Relation:0x000000055f8840>
any help would be appreciated.
任何帮助，将不胜感激。
回答by x1a4
A wherequery will return an ActiveRecord::Relation, which sort of acts like an array, even if you limit the number of returned records.
一个where查询将返回ActiveRecord::Relation，这有点像一个数组的行为，即使你限制返回的记录数。
If you instead change your query to:
如果您改为将查询更改为：
p = Person.where(id: 34).first
it will work as you want, and arel knows to automatically limit the query to a single result, so you don't have to explicitly specify limit(1).
它将按您的需要工作，并且 arel 知道自动将查询限制为单个结果，因此您不必明确指定limit(1).
You could also change to either
您也可以更改为
p = Person.find(34) # Throws an ActiveRecord::RecordNotFound exception if Person with id 34 does not exist
or
或者
p = Person.find_by_id(34) # Returns nil if Person with id 34 does not exist. Does *not* throw an exception.
and it will return a single record as expected.
它将按预期返回单个记录。
EDIT: A where query returns an ActiveRecord::Relation, as @mu is too shortmentioned in comments.
回答by Kevin Bedell
This returns a collection of active record objects:
这将返回活动记录对象的集合：
p = Person.where(id: 34).limit(1)
But there's only one with id = 34, so it's a collection of 1.
但是只有一个id = 34，所以它是1的集合。
The way to do this is:
这样做的方法是：
p = Person.where(id: 34).limit(1).first
or, better:
或更好：
p = Person.where(id: 34).first
or, even better:
或者，甚至更好：
p = Person.find(34)
回答by DVG
What you are probably actually looking for is
您可能实际上正在寻找的是
@person = Person.find(34)
@person.last_name
回答by Sai Ram Reddy
In your case Person is a class and it is inherited from ApplicationRecord
在您的情况下 Person 是一个类，它是从 ApplicationRecord 继承的
p = Person.where(id:10).limit(1)
It returns just the result of the query not the object.
它只返回查询的结果而不是对象。
You can check it by using
您可以使用
p.class # => It reurns Nilclass which means its not at all a class
So you cannot use p.last_name or p.first_name on p.
所以你不能在 p 上使用 p.last_name 或 p.first_name。
