Ruby-on-rails 检查 ActiveRecord find 是否返回结果
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Checking if ActiveRecord find returns a result
提问by nickcharlton
I'm trying to check if a find method returns a result. My find method is the following:
我正在尝试检查 find 方法是否返回结果。我的查找方法如下：
post = Post.find(:all, :conditions => { :url => params['url'] }, :limit => 1)
What would be a good way to check that postcontains a result?
检查post包含结果的好方法是什么？
回答by Jordan Running
find :allreturns an empty array ([]) if no rows are returned, so you can just use it this way:
find :all[]如果没有返回行，则返回一个空数组 ( )，因此您可以这样使用它：
post = Post.find(:all, :conditions => { :url => params['url'] }, :limit => 1)
unless post.empty?
# do something...
end
By the way, if you do find :allyou're going to get an array, not a single row. If you're trying to get just one Post, it would be cleaner to use the find_byhelper or find :firstor just firstinstead:
顺便说一句，如果你这样做，find :all你会得到一个数组，而不是一行。如果您只想获得一个 Post，则使用find_byhelper会更干净，find :first或者只是first代替：
post = Post.find_by_url params['url']
# or
post = Post.first :conditions => { :url => params['url'] }
# then...
if post
# do something...
end
回答by shingara
You can try ActiveRecord::Base.exists?before
你可以试试ActiveRecord::Base.exists？前
Post.exists?(:conditions => { :url => params['url'] })
回答by Ryan Bigg
Use the BANG!version of the find_by_urlmethod to get it to raise an exception of it could not be found and then rescue it later on in that same method/action.
使用砰！find_by_url无法找到使其引发异常的方法版本，然后稍后在同一方法/操作中拯救它。
def show
Post.find_by_url!(params[:url])
rescue ActiveRecord::RecordNotFound
flash[:notice] = "The URL you were looking for could not be found."
redirect_to root_path
end
end
If you didn't raise an exception here I believe that Rails would show the public/404.htmlpage.
如果您没有在这里提出异常，我相信 Rails 会显示public/404.html页面。
回答by Cristobal Viedma
if post doesn't contain any result it will be an empty list and then:
如果帖子不包含任何结果，它将是一个空列表，然后：
post.empty?
will return true.
将返回真。
回答by jamin4jc
it may be as simple as changing your finder to:
它可能就像将您的查找器更改为：
post = Post.find(:first, :conditions => { :url => params['url'] })
With this finder, post will either return a single value or nil. Because nil behaves like false in a condition statement, you can say something like the following:
使用此查找器，post 将返回单个值或 nil。因为 nil 在条件语句中表现得像 false，所以你可以这样说：
if post
# do something
else
# do something else
end
回答by boulder_ruby
Post.find_by_id(id_column_value)
will return nil rathering than blowing up your program when it can't find a record.
当它找不到记录时，将返回 nil 而不是炸毁你的程序。
Of course, there's
当然，还有
x = Post.where(:any_column_name => value)
which always returns an array of results. In which case you could just run an
它总是返回一个结果数组。在这种情况下，您可以运行一个
x.each {|t| f(t) }
or
或者
y = x.map {|t| f(t)}
or of course,
或者当然
x[0], x[1], etc
Sorry I got a little carried away there
对不起，我有点忘乎所以
回答by Vlad Cenan
Another way to do it is checking with ActiveRecord#any?.
另一种方法是使用ActiveRecord#any 进行检查？.
