查询唯一属性列表

Question

I created a Ruby array ( Articles ) with an attribute ( category ) containing repeating preset values (eg one of the following: "Drink", "Main", "Side" ). As result I'd like to get a list of all unique values of this category attribute.

I thought about something like

Article.all.category.uniq 

...but that didn't work. Here's an example array:

[#<Article id: 1, category: "Drink">, #<Article id: 2, category: "Main">, #<Article id: 3, category: "Drink">, #<Article id: 4, category: "Side">, #<Article id: 5, category: "Drink">, ] 

the content of the result list I am looking for should be in this case: "Drink", "Main", "Side"

Answer 1

Article.all.map {|a| a.category}.uniq

应该做的工作。

Answer 2

I'd do it like this:

Article.select("distinct category").map {|a| a.category}

rather than lucapette's answer , because that kind of operations are far slower in ruby than in a database.

My code example is assuming that you're using some kind of SQL database by the way. It would look different with other kinds of databases.

Answer 3

在Rails 3.2中

Article.uniq.pluck(:category)