Ruby-on-rails 如何将单列的值放入数组中
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How to get a single column's values into an array
提问by franklin stine
Right now I'm doing something like this to select a single column of data:
现在我正在做这样的事情来选择单列数据：
points = Post.find_by_sql("select point from posts")
Then passing them to a method, I'd like my method to remain agnostic, and now have to call hash.point from within my method. How can I quickly convert this into an array and pass the data set to my method, or is there a better way?
然后将它们传递给一个方法，我希望我的方法保持不可知，现在必须从我的方法中调用 hash.point。如何快速将其转换为数组并将数据集传递给我的方法，或者有更好的方法吗？
回答by alony
In Rails 3.2 there is a pluck methodfor this
在Rails 3.2有一个拔毛方法对本
Just like this:
像这样：
Person.pluck(:id) # SELECT people.id FROM people
Person.pluck(:role).uniq # unique roles from array of people
Person.distinct.pluck(:role) # SELECT DISTINCT role FROM people SQL
Person.where(:confirmed => true).limit(5).pluck(:id)
回答by Patrick Oscity
You should use the pluckmethod as @alony suggested. If you are stuck before Rails 3.2 you can use the ActiveRecord selectmethod together with Array#map:
您应该pluck按照@alony 的建议使用该方法。如果您在 Rails 3.2 之前卡住了，您可以将 ActiveRecordselect方法与Array#map：
Post.select(:point).map(&:point)
#=> ["foo", "bar", "baz"]
before Ruby 1.9 you'd have to do .map{|x| x.title}though, because Symbol#to_proc(aliased by the unary &operator) is not defined in earlier versions of Ruby.
在 Ruby 1.9 之前，你必须这样做.map{|x| x.title}，因为Symbol#to_proc（由一元运算&符别名）在早期版本的 Ruby 中没有定义。
回答by Vik
If you see the definition of select_values , then it using 'map(&:field_name)'
如果您看到 select_values 的定义，则它使用 'map(&:field_name)'
def select_values(arel, name = nil)
result = select_rows(to_sql(arel), name)
result.map { |v| v[0] }
end
The common and general Rails way to collect all the fields values in array is like :
收集数组中所有字段值的常见和通用 Rails 方法如下：
points = Post.all(:select => 'point').map(&:point)
回答by rajibchowdhury
points = Post.all.collect {|p| p.point}
